What is consciousness in one word

Consciousness, at its simplest, is sentience and awareness of internal and external existence.^[1] However, its nature has led to millennia of analyses, explanations and debates by philosophers, theologians, linguists, and scientists. Opinions differ about what exactly needs to be studied or even considered consciousness. In some explanations, it is synonymous with the mind, and at other times, an aspect of mind. In the past, it was one’s «inner life», the world of introspection, of private thought, imagination and volition.^[2] Today, it often includes any kind of cognition, experience, feeling or perception. It may be awareness, awareness of awareness, or self-awareness either continuously changing or not.^[3][4] The disparate range of research, notions and speculations raises a curiosity about whether the right questions are being asked.^[5]

Examples of the range of descriptions, definitions or explanations are: simple wakefulness, one’s sense of selfhood or soul explored by «looking within»; being a metaphorical «stream» of contents, or being a mental state, mental event or mental process of the brain.

Inter-disciplinary perspectives[edit]

Western philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. These questions remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively.

Consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology,^[6] neuropsychology and neuroscience. The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness.

In medicine, consciousness is assessed by observing a patient’s arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli.^[7] Issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted.^[8] The degree of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale.

Etymology[edit]

In the late 20th century, philosophers like Hamlyn, Rorty, and Wilkes have disagreed with Kahn, Hardie and Modrak as to whether Aristotle even had a concept of consciousness. Aristotle does not use any single word or terminology to name the phenomenon; it is used only much later, especially by John Locke. Caston contends that for Aristotle, perceptual awareness was somewhat the same as what modern philosophers call consciousness.^[9]

The origin of the modern concept of consciousness is often attributed to Locke’s Essay Concerning Human Understanding, published in 1690.^[10] Locke defined consciousness as «the perception of what passes in a man’s own mind».^[11] His essay influenced the 18th-century view of consciousness, and his definition appeared in Samuel Johnson’s celebrated Dictionary (1755).^[12]
«Consciousness» (French: conscience) is also defined in the 1753 volume of Diderot and d’Alembert’s Encyclopédie, as «the opinion or internal feeling that we ourselves have from what we do».^[13]

The earliest English language uses of «conscious» and «consciousness» date back, however, to the 1500s. The English word «conscious» originally derived from the Latin conscius (con- «together» and scio «to know»), but the Latin word did not have the same meaning as the English word—it meant «knowing with», in other words, «having joint or common knowledge with another».^[14] There were, however, many occurrences in Latin writings of the phrase conscius sibi, which translates literally as «knowing with oneself», or in other words «sharing knowledge with oneself about something». This phrase had the figurative meaning of «knowing that one knows», as the modern English word «conscious» does. In its earliest uses in the 1500s, the English word «conscious» retained the meaning of the Latin conscius. For example, Thomas Hobbes in Leviathan wrote: «Where two, or more men, know of one and the same fact, they are said to be Conscious of it one to another.»^[15] The Latin phrase conscius sibi, whose meaning was more closely related to the current concept of consciousness, was rendered in English as «conscious to oneself» or «conscious unto oneself». For example, Archbishop Ussher wrote in 1613 of «being so conscious unto myself of my great weakness».^[16] Locke’s definition from 1690 illustrates that a gradual shift in meaning had taken place.

A related word was conscientia, which primarily means moral conscience. In the literal sense, «conscientia» means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by writers such as Cicero.^[17] Here, conscientia is the knowledge that a witness has of the deed of someone else.^[18] René Descartes (1596–1650) is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning.^[19] Descartes used conscientia the way modern speakers would use «conscience». In Search after Truth (Regulæ ad directionem ingenii ut et inquisitio veritatis per lumen naturale, Amsterdam 1701) he says «conscience or internal testimony» (conscientiâ, vel interno testimonio).^[20][21]

The problem of definition[edit]

The dictionary definitions of the word consciousness extend through several centuries and reflect a range of seemingly related meanings, with some differences that have been controversial, such as the distinction between ‘inward awareness’ and ‘perception’ of the physical world, or the distinction between ‘conscious’ and ‘unconscious’, or the notion of a «mental entity» or «mental activity» that is not physical.

The common usage definitions of consciousness in Webster’s Third New International Dictionary (1966 edition, Volume 1, page 482) are as follows:

1. • awareness or perception of an inward psychological or spiritual fact; intuitively perceived knowledge of something in one’s inner self
   • inward awareness of an external object, state, or fact
   • concerned awareness; INTEREST, CONCERN—often used with an attributive noun [e.g. class consciousness]
2. the state or activity that is characterized by sensation, emotion, volition, or thought; mind in the broadest possible sense; something in nature that is distinguished from the physical
3. the totality in psychology of sensations, perceptions, ideas, attitudes, and feelings of which an individual or a group is aware at any given time or within a particular time span—compare STREAM OF CONSCIOUSNESS
4. waking life (as that to which one returns after sleep, trance, fever) wherein all one’s mental powers have returned . . .
5. the part of mental life or psychic content in psychoanalysis that is immediately available to the ego—compare PRECONSCIOUS, UNCONSCIOUS

The Cambridge Dictionary defines consciousness as «the state of understanding and realizing something.«^[23]
The Oxford Living Dictionary defines consciousness as «The state of being aware of and responsive to one’s surroundings.«, «A person’s awareness or perception of something.» and «The fact of awareness by the mind of itself and the world.«^[24]

Philosophers have attempted to clarify technical distinctions by using a jargon of their own. The Routledge Encyclopedia of Philosophy in 1998 defines consciousness as follows:

Consciousness—Philosophers have used the term ‘consciousness’ for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience… Something within one’s mind is ‘introspectively conscious’ just in case one introspects it (or is poised to do so). Introspection is often thought to deliver one’s primary knowledge of one’s mental life. An experience or other mental entity is ‘phenomenally conscious’ just in case there is ‘something it is like’ for one to have it. The clearest examples are: perceptual experience, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one’s own actions or perceptions; and streams of thought, as in the experience of thinking ‘in words’ or ‘in images’. Introspection and phenomenality seem independent, or dissociable, although this is controversial.^[25]

Many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness.^[26] In The Macmillan Dictionary of Psychology (1989 edition), Stuart Sutherland expressed a skeptical attitude more than a definition:

Consciousness—The having of perceptions, thoughts, and feelings; awareness. The term is impossible to define except in terms that are unintelligible without a grasp of what consciousness means. Many fall into the trap of equating consciousness with self-consciousness—to be conscious it is only necessary to be aware of the external world. Consciousness is a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it has evolved. Nothing worth reading has been written on it.^[26]

A partisan definition such as Sutherland’s can hugely affect researchers’ assumptions and the direction of their work:

If awareness of the environment . . . is the criterion of consciousness, then even the protozoans are conscious. If awareness of awareness is required, then it is doubtful whether the great apes and human infants are conscious.^[27]

Many philosophers have argued that consciousness is a unitary concept that is understood by the majority of people despite the difficulty philosophers have had defining it.^[28] Others, though, have argued that the level of disagreement about the meaning of the word indicates that it either means different things to different people (for instance, the objective versus subjective aspects of consciousness), that it encompasses a variety of distinct meanings with no simple element in common,^[29] or that we should eliminate this concept from our understanding of the mind, a position known as consciousness semanticism.^[30]

Philosophy of mind[edit]

Most writers on the philosophy of consciousness have been concerned with defending a particular point of view, and have organized their material accordingly. For surveys, the most common approach is to follow a historical path by associating stances with the philosophers who are most strongly associated with them, for example, Descartes, Locke, Kant, etc. An alternative is to organize philosophical stances according to basic issues.

Coherence of the concept[edit]

Philosophers differ from non-philosophers in their intuitions about what consciousness is.^[31] While most people have a strong intuition for the existence of what they refer to as consciousness,^[28] skeptics argue that this intuition is false, either because the concept of consciousness is intrinsically incoherent, or because our intuitions about it are based in illusions. Gilbert Ryle, for example, argued that traditional understanding of consciousness depends on a Cartesian dualist outlook that improperly distinguishes between mind and body, or between mind and world. He proposed that we speak not of minds, bodies, and the world, but of individuals, or persons, acting in the world. Thus, by speaking of «consciousness» we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.^[32]

Types[edit]

Ned Block argued that discussions on consciousness often failed to properly distinguish phenomenal (P-consciousness) from access (A-consciousness), though these terms had been used before Block.^[33] P-consciousness, according to Block, is raw experience: it is moving, colored forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. These experiences, considered independently of any impact on behavior, are called qualia. A-consciousness, on the other hand, is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. So, when we perceive, information about what we perceive is access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past is access conscious, and so on. Although some philosophers, such as Daniel Dennett, have disputed the validity of this distinction,^[34] others have broadly accepted it. David Chalmers has argued that A-consciousness can in principle be understood in mechanistic terms, but that understanding P-consciousness is much more challenging: he calls this the hard problem of consciousness.^[35]

Some philosophers believe that Block’s two types of consciousness are not the end of the story. William Lycan, for example, argued in his book Consciousness and Experience that at least eight clearly distinct types of consciousness can be identified (organism consciousness; control consciousness; consciousness of; state/event consciousness; reportability; introspective consciousness; subjective consciousness; self-consciousness)—and that even this list omits several more obscure forms.^[36]

There is also debate over whether or not A-consciousness and P-consciousness always coexist or if they can exist separately. Although P-consciousness without A-consciousness is more widely accepted, there have been some hypothetical examples of A without P. Block, for instance, suggests the case of a «zombie» that is computationally identical to a person but without any subjectivity. However, he remains somewhat skeptical concluding «I don’t know whether there are any actual cases of A-consciousness without P-consciousness, but I hope I have illustrated their conceptual possibility.»^[37]

Mind–body problem[edit]

Mental processes (such as consciousness) and physical processes (such as brain events) seem to be correlated, however the specific nature of the connection is unknown.

The first influential philosopher to discuss this question specifically was Descartes, and the answer he gave is known as Cartesian dualism. Descartes proposed that consciousness resides within an immaterial domain he called res cogitans (the realm of thought), in contrast to the domain of material things, which he called res extensa (the realm of extension).^[38] He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.^[39]

Although it is widely accepted that Descartes explained the problem cogently, few later philosophers have been happy with his solution, and his ideas about the pineal gland have especially been ridiculed.^[40] However, no alternative solution has gained general acceptance. Proposed solutions can be divided broadly into two categories: dualist solutions that maintain Descartes’s rigid distinction between the realm of consciousness and the realm of matter but give different answers for how the two realms relate to each other; and monist solutions that maintain that there is really only one realm of being, of which consciousness and matter are both aspects. Each of these categories itself contains numerous variants. The two main types of dualism are substance dualism (which holds that the mind is formed of a distinct type of substance not governed by the laws of physics) and property dualism (which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of monism are physicalism (which holds that the mind consists of matter organized in a particular way), idealism (which holds that only thought or experience truly exists, and matter is merely an illusion), and neutral monism (which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them). There are also, however, a large number of idiosyncratic theories that cannot cleanly be assigned to any of these schools of thought.^[41]

Since the dawn of Newtonian science with its vision of simple mechanical principles governing the entire universe, some philosophers have been tempted by the idea that consciousness could be explained in purely physical terms. The first influential writer to propose such an idea explicitly was Julien Offray de La Mettrie, in his book Man a Machine (L’homme machine). His arguments, however, were very abstract.^[42] The most influential modern physical theories of consciousness are based on psychology and neuroscience. Theories proposed by neuroscientists such as Gerald Edelman^[43] and Antonio Damasio,^[44] and by philosophers such as Daniel Dennett,^[45] seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as Christof Koch,^[46] have explored the neural basis of consciousness without attempting to frame all-encompassing global theories. At the same time, computer scientists working in the field of artificial intelligence have pursued the goal of creating digital computer programs that can simulate or embody consciousness.^[47]

A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, but that quantum theory may provide the missing ingredients. Several theorists have therefore proposed quantum mind (QM) theories of consciousness.^[48] Notable theories falling into this category include the holonomic brain theory of Karl Pribram and David Bohm, and the Orch-OR theory formulated by Stuart Hameroff and Roger Penrose. Some of these QM theories offer descriptions of phenomenal consciousness, as well as QM interpretations of access consciousness. None of the quantum mechanical theories have been confirmed by experiment. Recent publications by G. Guerreshi, J. Cia, S. Popescu, and H. Briegel^[49] could falsify proposals such as those of Hameroff, which rely on quantum entanglement in protein. At the present time many scientists and philosophers consider the arguments for an important role of quantum phenomena to be unconvincing.^[50]

Apart from the general question of the «hard problem» of consciousness (which is, roughly speaking, the question of how mental experience can arise from a physical basis^[51]), a more specialized question is how to square the subjective notion that we are in control of our decisions (at least in some small measure) with the customary view of causality that subsequent events are caused by prior events. The topic of free will is the philosophical and scientific examination of this conundrum.

Problem of other minds[edit]

Many philosophers consider experience to be the essence of consciousness, and believe that experience can only fully be known from the inside, subjectively. But if consciousness is subjective and not visible from the outside, why do the vast majority of people believe that other people are conscious, but rocks and trees are not?^[52] This is called the problem of other minds.^[53] It is particularly acute for people who believe in the possibility of philosophical zombies, that is, people who think it is possible in principle to have an entity that is physically indistinguishable from a human being and behaves like a human being in every way but nevertheless lacks consciousness.^[54] Related issues have also been studied extensively by Greg Littmann of the University of Illinois,^[55] and by Colin Allen (a professor at the University of Pittsburgh) regarding the literature and research studying artificial intelligence in androids.^[56]

The most commonly given answer is that we attribute consciousness to other people because we see that they resemble us in appearance and behavior; we reason that if they look like us and act like us, they must be like us in other ways, including having experiences of the sort that we do.^[57] There are, however, a variety of problems with that explanation. For one thing, it seems to violate the principle of parsimony, by postulating an invisible entity that is not necessary to explain what we observe.^[57] Some philosophers, such as Daniel Dennett in a research paper titled «The Unimagined Preposterousness of Zombies», argue that people who give this explanation do not really understand what they are saying.^[58] More broadly, philosophers who do not accept the possibility of zombies generally believe that consciousness is reflected in behavior (including verbal behavior), and that we attribute consciousness on the basis of behavior. A more straightforward way of saying this is that we attribute experiences to people because of what they can do, including the fact that they can tell us about their experiences.^[59]

Scientific study[edit]

For many decades, consciousness as a research topic was avoided by the majority of mainstream scientists, because of a general feeling that a phenomenon defined in subjective terms could not properly be studied using objective experimental methods.^[60] In 1975 George Mandler published an influential psychological study which distinguished between slow, serial, and limited conscious processes and fast, parallel and extensive unconscious ones.^[61] The Science and Religion Forum^[62] 1984 annual conference, ‘From Artificial Intelligence to Human Consciousness‘ identified the nature of consciousness as a matter for investigation; Donald Michie was a keynote speaker. Starting in the 1980s, an expanding community of neuroscientists and psychologists have associated themselves with a field called Consciousness Studies, giving rise to a stream of experimental work published in books,^[63] journals such as Consciousness and Cognition, Frontiers in Consciousness Research, Psyche, and the Journal of Consciousness Studies, along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness^[64] and the Society for Consciousness Studies.

Modern medical and psychological investigations into consciousness are based on psychological experiments (including, for example, the investigation of priming effects using subliminal stimuli), and on case studies of alterations in consciousness produced by trauma, illness, or drugs. Broadly viewed, scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In either case, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.^[46]

Measurement[edit]

Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted operational definition. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion used is verbal report: in other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness.^[65] For example, subjects who stare continuously at a Necker cube usually report that they experience it «flipping» between two 3D configurations, even though the stimulus itself remains the same.^[66] The objective is to understand the relationship between the conscious awareness of stimuli (as indicated by verbal report) and the effects the stimuli have on brain activity and behavior. In several paradigms, such as the technique of response priming, the behavior of subjects is clearly influenced by stimuli for which they report no awareness, and suitable experimental manipulations can lead to increasing priming effects despite decreasing prime identification (double dissociation).^[67]

Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.^[68] For one thing, if verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected.^[69] Daniel Dennett has argued for an approach he calls heterophenomenology, which means treating verbal reports as stories that may or may not be true, but his ideas about how to do this have not been widely adopted.^[70] Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language: this approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. As a third issue, philosophers who dispute the validity of the Turing test may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness.^[71]

Although verbal report is in practice the «gold standard» for ascribing consciousness, it is not the only possible criterion.^[68] In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent.^[72][73] The scientific literature regarding the neural bases of arousal and purposeful movement is very extensive. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness.^[67] Studies of the neuroscience of free will have also shown that the experiences that people report when they behave purposefully sometimes do not correspond to their actual behaviors or to the patterns of electrical activity recorded from their brains.^[74]

Another approach applies specifically to the study of self-awareness, that is, the ability to distinguish oneself from others. In the 1970s Gordon Gallup developed an operational test for self-awareness, known as the mirror test. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual’s forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves.^[75] Humans (older than 18 months) and other great apes, bottlenose dolphins, orcas, pigeons, European magpies and elephants have all been observed to pass this test.^[76]

Neural correlates[edit]

A major part of the scientific literature on consciousness consists of studies that examine the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the neural correlates of consciousness. The hope is to find that activity in a particular part of the brain, or a particular pattern of global brain activity, which will be strongly predictive of conscious awareness. Several brain imaging techniques, such as EEG and fMRI, have been used for physical measures of brain activity in these studies.^[77]

Another idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) oscillations in brain activity. This idea arose from proposals in the 1980s, by Christof von der Malsburg and Wolf Singer, that gamma oscillations could solve the so-called binding problem, by linking information represented in different parts of the brain into a unified experience.^[78] Rodolfo Llinás, for example, proposed that consciousness results from recurrent thalamo-cortical resonance where the specific thalamocortical systems (content) and the non-specific (centromedial thalamus) thalamocortical systems (context) interact in the gamma band frequency via synchronous oscillations.^[79]

A number of studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness: it is possible for subjects to report a lack of awareness even when areas such as the primary visual cortex (V1) show clear electrical responses to a stimulus.^[80] Higher brain areas are seen as more promising, especially the prefrontal cortex, which is involved in a range of higher cognitive functions collectively known as executive functions.^[81] There is substantial evidence that a «top-down» flow of neural activity (i.e., activity propagating from the frontal cortex to sensory areas) is more predictive of conscious awareness than a «bottom-up» flow of activity.^[82] The prefrontal cortex is not the only candidate area, however: studies by Nikos Logothetis and his colleagues have shown, for example, that visually responsive neurons in parts of the temporal lobe reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry).^[83] Furthermore, top-down feedback from higher to lower visual brain areas may be weaker or absent in the peripheral visual field, as suggested by some experimental data and theoretical arguments;^[84] nevertheless humans can perceive visual inputs in the peripheral visual field arising from bottom-up V1 neural activities.^[84][85] Meanwhile, bottom-up V1 activities for the central visual fields can be vetoed, and thus made invisible to perception, by the top-down feedback, when these bottom-up signals are inconsistent with brain’s internal model of the visual world.^[84][85]

Modulation of neural responses may correlate with phenomenal experiences. In contrast to the raw electrical responses that do not correlate with consciousness, the modulation of these responses by other stimuli correlates surprisingly well with an important aspect of consciousness: namely with the phenomenal experience of stimulus intensity (brightness, contrast). In the research group of Danko Nikolić it has been shown that some of the changes in the subjectively perceived brightness correlated with the modulation of firing rates while others correlated with the modulation of neural synchrony.^[86] An fMRI investigation suggested that these findings were strictly limited to the primary visual areas.^[87] This indicates that, in the primary visual areas, changes in firing rates and synchrony can be considered as neural correlates of qualia—at least for some type of qualia.

In 2013, the perturbational complexity index (PCI) was proposed, a measure of the algorithmic complexity of the electrophysiological response of the cortex to transcranial magnetic stimulation. This measure was shown to be higher in individuals that are awake, in REM sleep or in a locked-in state than in those who are in deep sleep or in a vegetative state,^[88] making it potentially useful as a quantitative assessment of consciousness states.

Assuming that not only humans but even some non-mammalian species are conscious, a number of evolutionary approaches to the problem of neural correlates of consciousness open up. For example, assuming that birds are conscious—a common assumption among neuroscientists and ethologists due to the extensive cognitive repertoire of birds—there are comparative neuroanatomical ways to validate some of the principal, currently competing, mammalian consciousness–brain theories. The rationale for such a comparative study is that the avian brain deviates structurally from the mammalian brain. So how similar are they? What homologues can be identified? The general conclusion from the study by Butler, et al.,^[89] is that some of the major theories for the mammalian brain ^[90][91][92] also appear to be valid for the avian brain. The structures assumed to be critical for consciousness in mammalian brains have homologous counterparts in avian brains. Thus the main portions of the theories of Crick and Koch,^[90] Edelman and Tononi,^[91] and Cotterill ^[92] seem to be compatible with the assumption that birds are conscious. Edelman also differentiates between what he calls primary consciousness (which is a trait shared by humans and non-human animals) and higher-order consciousness as it appears in humans alone along with human language capacity.^[91] Certain aspects of the three theories, however, seem less easy to apply to the hypothesis of avian consciousness. For instance, the suggestion by Crick and Koch that layer 5 neurons of the mammalian brain have a special role, seems difficult to apply to the avian brain, since the avian homologues have a different morphology. Likewise, the theory of Eccles^[93][94] seems incompatible, since a structural homologue/analogue to the dendron has not been found in avian brains. The assumption of an avian consciousness also brings the reptilian brain into focus. The reason is the structural continuity between avian and reptilian brains, meaning that the phylogenetic origin of consciousness may be earlier than suggested by many leading neuroscientists.

Joaquin Fuster of UCLA has advocated the position of the importance of the prefrontal cortex in humans, along with the areas of Wernicke and Broca, as being of particular importance to the development of human language capacities neuro-anatomically necessary for the emergence of higher-order consciousness in humans.^[95]

A study in 2016 looked at lesions in specific areas of the brainstem that were associated with coma and vegetative states. A small region of the rostral dorsolateral pontine tegmentum in the brainstem was suggested to drive consciousness through functional connectivity with two cortical regions, the left ventral anterior insular cortex, and the pregenual anterior cingulate cortex. These three regions may work together as a triad to maintain consciousness.^[96]

Models[edit]

This section is missing information about global workspace theory. Please expand the section to include this information. Further details may exist on the talk page. (January 2023)

A wide range of empirical theories of consciousness have been proposed.^[97][98][99] Adrian Doerig and colleagues list 13 notable theories,^[99] while Anil Seth and Tim Bayne list 22 notable theories.^[98]

Integrated information theory (IIT) postulates that consciousness resides in the information being processed and arises once the information reaches a certain level of complexity.^{[citation needed]}

Orchestrated objective reduction (Orch OR) postulates that consciousness originates at the quantum level inside neurons. The mechanism is held to be a quantum process called objective reduction that is orchestrated by cellular structures called microtubules. However the details of the mechanism would go beyond current quantum theory.^[100]

In 2011, Graziano and Kastner^[101] proposed the «attention schema» theory of awareness. In that theory, specific cortical areas, notably in the superior temporal sulcus and the temporo-parietal junction, are used to build the construct of awareness and attribute it to other people. The same cortical machinery is also used to attribute awareness to oneself. Damage to these cortical regions can lead to deficits in consciousness such as hemispatial neglect. In the attention schema theory, the value of explaining the feature of awareness and attributing it to a person is to gain a useful predictive model of that person’s attentional processing. Attention is a style of information processing in which a brain focuses its resources on a limited set of interrelated signals. Awareness, in this theory, is a useful, simplified schema that represents attentional states. To be aware of X is explained by constructing a model of one’s attentional focus on X.

The entropic brain is a theory of conscious states informed by neuroimaging research with psychedelic drugs. The theory suggests that the brain in primary states such as rapid eye movement (REM) sleep, early psychosis and under the influence of psychedelic drugs, is in a disordered state; normal waking consciousness constrains some of this freedom and makes possible metacognitive functions such as internal self-administered reality testing and self-awareness.^{[102][103][104][105]} Criticism has included questioning whether the theory has been adequately tested.^[106]

In 2017, work by David Rudrauf and colleagues, including Karl Friston, applied the active inference paradigm to consciousness, a model of how sensory data is integrated with priors in a process of projective transformation. The authors argue that, while their model identifies a key relationship between computation and phenomenology, it does not completely solve the hard problem of consciousness or completely close the explanatory gap.^[107]

Biological function and evolution[edit]

Opinions are divided as to where in biological evolution consciousness emerged and about whether or not consciousness has any survival value. Some argue that consciousness is a byproduct of evolution. It has been argued that consciousness emerged (i) exclusively with the first humans, (ii) exclusively with the first mammals, (iii) independently in mammals and birds, or (iv) with the first reptiles.^[108] Other authors date the origins of consciousness to the first animals with nervous systems or early vertebrates in the Cambrian over 500 million years ago.^[109] Donald Griffin suggests in his book Animal Minds a gradual evolution of consciousness.^[110] Each of these scenarios raises the question of the possible survival value of consciousness.

Thomas Henry Huxley defends in an essay titled On the Hypothesis that Animals are Automata, and its History an epiphenomenalist theory of consciousness according to which consciousness is a causally inert effect of neural activity—»as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery».^[111] To this William James objects in his essay Are We Automata? by stating an evolutionary argument for mind-brain interaction implying that if the preservation and development of consciousness in the biological evolution is a result of natural selection, it is plausible that consciousness has not only been influenced by neural processes, but has had a survival value itself; and it could only have had this if it had been efficacious.^[112][113] Karl Popper develops in the book The Self and Its Brain a similar evolutionary argument.^[114]

Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent.^[115] This has been called the integration consensus. Another example has been proposed by Gerald Edelman called dynamic core hypothesis which puts emphasis on reentrant connections that reciprocally link areas of the brain in a massively parallel manner.^[116] Edelman also stresses the importance of the evolutionary emergence of higher-order consciousness in humans from the historically older trait of primary consciousness which humans share with non-human animals (see Neural correlates section above). These theories of integrative function present solutions to two classic problems associated with consciousness: differentiation and unity. They show how our conscious experience can discriminate between a virtually unlimited number of different possible scenes and details (differentiation) because it integrates those details from our sensory systems, while the integrative nature of consciousness in this view easily explains how our experience can seem unified as one whole despite all of these individual parts. However, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect.^[117] Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see the article of Ezequiel Morsella.^[117]

As noted earlier, even among writers who consider consciousness to be well-defined, there is widespread dispute about which animals other than humans can be said to possess it.^[118] Edelman has described this distinction as that of humans possessing higher-order consciousness while sharing the trait of primary consciousness with non-human animals (see previous paragraph). Thus, any examination of the evolution of consciousness is faced with great difficulties. Nevertheless, some writers have argued that consciousness can be viewed from the standpoint of evolutionary biology as an adaptation in the sense of a trait that increases fitness.^[119] In his article «Evolution of consciousness», John Eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness («[a] psychon … linked to [a] dendron through quantum physics»).^[120] Bernard Baars proposed that once in place, this «recursive» circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms.^[121] Peter Carruthers has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality.^[122] This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends.

Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes.^[123][124] No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function F being performed by conscious organism O and non-conscious organism O*, it is unclear what adaptive advantage consciousness could provide.^[125] As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an exaptation arising as a consequence of other developments such as increases in brain size or cortical rearrangement.^[109] Consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired.^[126] Several scholars including Pinker, Chomsky, Edelman, and Luria have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness (see Neural correlates section above).

Altered states[edit]

There are some brain states in which consciousness seems to be absent, including dreamless sleep or coma. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage.^[127] Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance.^[128]

The two most widely accepted altered states are sleep and dreaming. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions.^{[129][failed verification]} Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed.^[130]

Research conducted on the effects of partial epileptic seizures on consciousness found that patients who have partial epileptic seizures experience altered states of consciousness.^[131][132] In partial epileptic seizures, consciousness is impaired or lost while some aspects of consciousness, often automated behaviors, remain intact. Studies found that when measuring the qualitative features during partial epileptic seizures, patients exhibited an increase in arousal and became absorbed in the experience of the seizure, followed by difficulty in focusing and shifting attention.

A variety of psychoactive drugs, including alcohol, have notable effects on consciousness.^[133] These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, empathogens–entactogens such as MDMA («Ecstasy»), or most notably by the class of drugs known as psychedelics.^[127] LSD, mescaline, psilocybin, dimethyltryptamine, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. The brain mechanisms underlying these effects are not as well understood as those induced by use of alcohol,^[133] but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter serotonin play an essential role.^[134]

There has been some research into physiological changes in yogis and people who practise various techniques of meditation. Some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. It has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness.^[135]

The most extensive study of the characteristics of altered states of consciousness was made by psychologist Charles Tart in the 1960s and 1970s. Tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world); interoception (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment.^{[136][self-published source]} Each of these, in his view, could be altered in multiple ways by drugs or other manipulations. The components that Tart identified have not, however, been validated by empirical studies. Research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual synesthesia; and changed meaning of percepts.^[137]

Medical aspects[edit]

The medical approach to consciousness is scientifically oriented. It derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. In medicine, conceptual distinctions are considered useful to the degree that they can help to guide treatments. The medical approach focuses mostly on the amount of consciousness a person has: in medicine, consciousness is assessed as a «level» ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end.^[138]

Consciousness is of concern to patients and physicians, especially neurologists and anesthesiologists. Patients may have disorders of consciousness or may need to be anesthetized for a surgical procedure. Physicians may perform consciousness-related interventions such as instructing the patient to sleep, administering general anesthesia, or inducing medical coma.^[138] Also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as the Karen Ann Quinlan case,^[139] while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.^[140]

Assessment[edit]

In medicine, consciousness is examined using a set of procedures known as neuropsychological assessment.^[72] There are two commonly used methods for assessing the level of consciousness of a patient: a simple procedure that requires minimal training, and a more complex procedure that requires substantial expertise. The simple procedure begins by asking whether the patient is able to move and react to physical stimuli. If so, the next question is whether the patient can respond in a meaningful way to questions and commands. If so, the patient is asked for name, current location, and current day and time. A patient who can answer all of these questions is said to be «alert and oriented times four» (sometimes denoted «A&Ox4» on a medical chart), and is usually considered fully conscious.^[141]

The more complex procedure is known as a neurological examination, and is usually carried out by a neurologist in a hospital setting. A formal neurological examination runs through a precisely delineated series of tests, beginning with tests for basic sensorimotor reflexes, and culminating with tests for sophisticated use of language. The outcome may be summarized using the Glasgow Coma Scale, which yields a number in the range 3–15, with a score of 3 to 8 indicating coma, and 15 indicating full consciousness. The Glasgow Coma Scale has three subscales, measuring the best motor response (ranging from «no motor response» to «obeys commands»), the best eye response (ranging from «no eye opening» to «eyes opening spontaneously») and the best verbal response (ranging from «no verbal response» to «fully oriented»). There is also a simpler pediatric version of the scale, for children too young to be able to use language.^[138]

In 2013, an experimental procedure was developed to measure degrees of consciousness, the procedure involving stimulating the brain with a magnetic pulse, measuring resulting waves of electrical activity, and developing a consciousness score based on the complexity of the brain activity.^[142]

Disorders[edit]

Medical conditions that inhibit consciousness are considered disorders of consciousness.^[143] This category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma.^[143][144] Differential diagnosis of these disorders is an active area of biomedical research.^{[145][146][147]} Finally, brain death results in possible irreversible disruption of consciousness.^[143] While other conditions may cause a moderate deterioration (e.g., dementia and delirium) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category.

Disorder	Description
Locked-in syndrome	The patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy.
Minimally conscious state	The patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior.
Persistent vegetative state	The patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior.
Chronic coma	The patient lacks awareness and sleep-wake cycles and only displays reflexive behavior.
Brain death	The patient lacks awareness, sleep-wake cycles, and brain-mediated reflexive behavior.

Medical experts increasingly view anosognosia as a disorder of consciousness.^[148] Anosognosia a Greek-derived term meaning «unawareness of disease». This is a condition in which patients are disabled in some way, most commonly as a result of a stroke, but either misunderstand the nature of the problem or deny that there is anything wrong with them.^[149] The most frequently occurring form is seen in people who have experienced a stroke damaging the parietal lobe in the right hemisphere of the brain, giving rise to a syndrome known as hemispatial neglect, characterized by an inability to direct action or attention toward objects located to the left with respect to their bodies. Patients with hemispatial neglect are often paralyzed on the left side of the body, but sometimes deny being unable to move. When questioned about the obvious problem, the patient may avoid giving a direct answer, or may give an explanation that doesn’t make sense. Patients with hemispatial neglect may also fail to recognize paralyzed parts of their bodies: one frequently mentioned case is of a man who repeatedly tried to throw his own paralyzed right leg out of the bed he was lying in, and when asked what he was doing, complained that somebody had put a dead leg into the bed with him. An even more striking type of anosognosia is Anton–Babinski syndrome, a rarely occurring condition in which patients become blind but claim to be able to see normally, and persist in this claim in spite of all evidence to the contrary.^[150]

Outside human adults[edit]

In children[edit]

Of the eight types of consciousness in the Lycan classification, some are detectable in utero and others develop years after birth. Psychologist and educator William Foulkes studied children’s dreams and concluded that prior to the shift in cognitive maturation that humans experience during ages five to seven,^[151] children lack the Lockean consciousness that Lycan had labeled «introspective consciousness» and that Foulkes labels «self-reflection.»^[152] In a 2020 paper, Katherine Nelson and Robyn Fivush use «autobiographical consciousness» to label essentially the same faculty, and agree with Foulkes on the timing of this faculty’s acquisition. Nelson and Fivush contend that «language is the tool by which humans create a new, uniquely human form of consciousness, namely, autobiographical consciousness.»^[153] Julian Jaynes had staked out these positions decades earlier.^[154][155] Citing the developmental steps that lead the infant to autobiographical consciousness, Nelson and Fivush point to the acquisition of «theory of mind,» calling theory of mind «necessary for autobiographical consciousness» and defining it as «understanding differences between one’s own mind and others’ minds in terms of beliefs, desires, emotions and thoughts.» They write, «The hallmark of theory of mind, the understanding of false belief, occurs … at five to six years of age.»^[156]

In animals[edit]

The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because non-human animals, lacking the ability to express human language, cannot tell humans about their experiences.^[157] Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Descartes, for example, has sometimes been blamed for mistreatment of animals due to the fact that he believed only humans have a non-physical mind.^[158] Most people have a strong intuition that some animals, such as cats and dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious, and are often based on personal interactions with pets and other animals they have observed.^[157]

Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled What Is it Like to Be a Bat?. He said that an organism is conscious «if and only if there is something that it is like to be that organism—something it is like for the organism»; and he argued that no matter how much we know about an animal’s brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself.^[159] Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent.^[160] Several psychologists and ethologists have argued for the existence of animal consciousness by describing a range of behaviors that appear to show animals holding beliefs about things they cannot directly perceive—Donald Griffin’s 2001 book Animal Minds reviews a substantial portion of the evidence.^[110]

On July 7, 2012, eminent scientists from different branches of neuroscience gathered at the University of Cambridge to celebrate the Francis Crick Memorial Conference, which deals with consciousness in humans and pre-linguistic consciousness in nonhuman animals. After the conference, they signed in the presence of Stephen Hawking, the ‘Cambridge Declaration on Consciousness’, which summarizes the most important findings of the survey:

«We decided to reach a consensus and make a statement directed to the public that is not scientific. It’s obvious to everyone in this room that animals have consciousness, but it is not obvious to the rest of the world. It is not obvious to the rest of the Western world or the Far East. It is not obvious to the society.»^[161]

«Convergent evidence indicates that non-human animals …, including all mammals and birds, and other creatures, … have the necessary neural substrates of consciousness and the capacity to exhibit intentional behaviors.»^[162]

In artifacts[edit]

The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the Golem, a magically animated homunculus built of clay.^[163] However, the possibility of actually constructing a conscious machine was probably first discussed by Ada Lovelace, in a set of notes written in 1842 about the Analytical Engine invented by Charles Babbage, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a humanlike way. She wrote:

It is desirable to guard against the possibility of exaggerated ideas that might arise as to the powers of the Analytical Engine. … The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its province is to assist us in making available what we are already acquainted with.^[164]

One of the most influential contributions to this question was an essay written in 1950 by pioneering computer scientist Alan Turing, titled Computing Machinery and Intelligence. Turing disavowed any interest in terminology, saying that even «Can machines think?» is too loaded with spurious connotations to be meaningful; but he proposed to replace all such questions with a specific operational test, which has become known as the Turing test.^[165] To pass the test, a computer must be able to imitate a human well enough to fool interrogators. In his essay Turing discussed a variety of possible objections, and presented a counterargument to each of them. The Turing test is commonly cited in discussions of artificial intelligence as a proposed criterion for machine consciousness; it has provoked a great deal of philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious,^[166] while David Chalmers argues that a philosophical zombie could pass the test, yet fail to be conscious.^[167] A third group of scholars have argued that with technological growth once machines begin to display any substantial signs of human-like behavior then the dichotomy (of human consciousness compared to human-like consciousness) becomes passé and issues of machine autonomy begin to prevail even as observed in its nascent form within contemporary industry and technology.^[55][56] Jürgen Schmidhuber argues that consciousness is the result of compression.^[168] As an agent sees representation of itself recurring in the environment, the compression of this representation can be called consciousness.

In a lively exchange over what has come to be referred to as «the Chinese room argument», John Searle sought to refute the claim of proponents of what he calls «strong artificial intelligence (AI)» that a computer program can be conscious, though he does agree with advocates of «weak AI» that computer programs can be formatted to «simulate» conscious states. His own view is that consciousness has subjective, first-person causal powers by being essentially intentional due to the way human brains function biologically; conscious persons can perform computations, but consciousness is not inherently computational the way computer programs are. To make a Turing machine that speaks Chinese, Searle imagines a room with one monolingual English speaker (Searle himself, in fact), a book that designates a combination of Chinese symbols to be output paired with Chinese symbol input, and boxes filled with Chinese symbols. In this case, the English speaker is acting as a computer and the rulebook as a program. Searle argues that with such a machine, he would be able to process the inputs to outputs perfectly without having any understanding of Chinese, nor having any idea what the questions and answers could possibly mean. If the experiment were done in English, since Searle knows English, he would be able to take questions and give answers without any algorithms for English questions, and he would be effectively aware of what was being said and the purposes it might serve. Searle would pass the Turing test of answering the questions in both languages, but he is only conscious of what he is doing when he speaks English. Another way of putting the argument is to say that computer programs can pass the Turing test for processing the syntax of a language, but that the syntax cannot lead to semantic meaning in the way strong AI advocates hoped.^[169][170]

In the literature concerning artificial intelligence, Searle’s essay has been second only to Turing’s in the volume of debate it has generated.^[171] Searle himself was vague about what extra ingredients it would take to make a machine conscious: all he proposed was that what was needed was «causal powers» of the sort that the brain has and that computers lack. But other thinkers sympathetic to his basic argument have suggested that the necessary (though perhaps still not sufficient) extra conditions may include the ability to pass not just the verbal version of the Turing test, but the robotic version,^[172] which requires grounding the robot’s words in the robot’s sensorimotor capacity to categorize and interact with the things in the world that its words are about, Turing-indistinguishably from a real person. Turing-scale robotics is an empirical branch of research on embodied cognition and situated cognition.^[173]

In 2014, Victor Argonov has suggested a non-Turing test for machine consciousness based on machine’s ability to produce philosophical judgments.^[174] He argues that a deterministic machine must be regarded as conscious if it is able to produce judgments on all problematic properties of consciousness (such as qualia or binding) having no innate (preloaded) philosophical knowledge on these issues, no philosophical discussions while learning, and no informational models of other creatures in its memory (such models may implicitly or explicitly contain knowledge about these creatures’ consciousness). However, this test can be used only to detect, but not refute the existence of consciousness. A positive result proves that machine is conscious but a negative result proves nothing. For example, absence of philosophical judgments may be caused by lack of the machine’s intellect, not by absence of consciousness.

Stream of consciousness[edit]

William James is usually credited with popularizing the idea that human consciousness flows like a stream, in his Principles of Psychology of 1890.

According to James, the «stream of thought» is governed by five characteristics:^[175]

1. Every thought tends to be part of a personal consciousness.
2. Within each personal consciousness thought is always changing.
3. Within each personal consciousness thought is sensibly continuous.
4. It always appears to deal with objects independent of itself.
5. It is interested in some parts of these objects to the exclusion of others.

A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or «mental continuum». Buddhist teachings describe that consciousness manifests moment to moment as sense impressions and mental phenomena that are continuously changing.^[176] The teachings list six triggers that can result in the generation of different mental events.^[176] These triggers are input from the five senses (seeing, hearing, smelling, tasting or touch sensations), or a thought (relating to the past, present or the future) that happen to arise in the mind. The mental events generated as a result of these triggers are: feelings, perceptions and intentions/behaviour. The moment-by-moment manifestation of the mind-stream is said to happen in every person all the time. It even happens in a scientist who analyses various phenomena in the world, or analyses the material body including the organ brain.^[176] The manifestation of the mindstream is also described as being influenced by physical laws, biological laws, psychological laws, volitional laws, and universal laws.^[176] The purpose of the Buddhist practice of mindfulness is to understand the inherent nature of the consciousness and its characteristics.^[177]

Narrative form[edit]

In the West, the primary impact of the idea has been on literature rather than science: «stream of consciousness as a narrative mode» means writing in a way that attempts to portray the moment-to-moment thoughts and experiences of a character. This technique perhaps had its beginnings in the monologues of Shakespeare’s plays and reached its fullest development in the novels of James Joyce and Virginia Woolf, although it has also been used by many other noted writers.^[178]

Here, for example, is a passage from Joyce’s Ulysses about the thoughts of Molly Bloom:

Yes because he never did a thing like that before as ask to get his breakfast in bed with a couple of eggs since the City Arms hotel when he used to be pretending to be laid up with a sick voice doing his highness to make himself interesting for that old faggot Mrs Riordan that he thought he had a great leg of and she never left us a farthing all for masses for herself and her soul greatest miser ever was actually afraid to lay out 4d for her methylated spirit telling me all her ailments she had too much old chat in her about politics and earthquakes and the end of the world let us have a bit of fun first God help the world if all the women were her sort down on bathingsuits and lownecks of course nobody wanted her to wear them I suppose she was pious because no man would look at her twice I hope Ill never be like her a wonder she didnt want us to cover our faces but she was a welleducated woman certainly and her gabby talk about Mr Riordan here and Mr Riordan there I suppose he was glad to get shut of her.^[179]

Spiritual approaches[edit]

To most philosophers, the word «consciousness» connotes the relationship between the mind and the world. To writers on spiritual or religious topics, it frequently connotes the relationship between the mind and God, or the relationship between the mind and deeper truths that are thought to be more fundamental than the physical world. The mystical psychiatrist Richard Maurice Bucke, author of the 1901 book Cosmic Consciousness: A Study in the Evolution of the Human Mind,
distinguished between three types of consciousness: ‘Simple Consciousness’, awareness of the body, possessed by many animals; ‘Self Consciousness’, awareness of being aware, possessed only by humans; and ‘Cosmic Consciousness’, awareness of the life and order of the universe, possessed only by humans who are enlightened.^[180] Many more examples could be given, such as the various levels of spiritual consciousness presented by Prem Saran Satsangi and Stuart Hameroff.^[181]

Another thorough account of the spiritual approach is Ken Wilber’s 1977 book The Spectrum of Consciousness, a comparison of western and eastern ways of thinking about the mind. Wilber described consciousness as a spectrum with ordinary awareness at one end, and more profound types of awareness at higher levels.^[182]

See also[edit]

• Chaitanya (consciousness): Pure consciousness in Hindu philosophy.
• Models of consciousness: Ideas for a scientific mechanism underlying consciousness.
• Plant perception (paranormal): A pseudoscientific theory.
• Sakshi (Witness): Pure awareness in Hindu philosophy.
• Vertiginous question: On the uniqueness of a person’s consciousness.

References[edit]

Further reading[edit]

External links[edit]

This awareness is subjective and unique to you. If you can describe something you are experiencing in words, then it is part of your consciousness.

Your conscious experiences are constantly shifting and changing. For example, in one moment you may be focused on reading this article. Your consciousness may then shift to the memory of a conversation you had earlier with a co-worker. Next, you might notice how uncomfortable your chair is, or maybe you are mentally planning dinner.

Types of Consciousness

The various states of consciousness include:

• Dreams
• Hallucinations
• Hypnosis
• Meditation
• Sleep
• States induced by psychoactive drugs

The two normal states of awareness are consciousness and unconsciousness. Altered levels of consciousness also can occur, which may be caused by medical or mental conditions that impair or change awareness. 

Altered types of consciousness include:

• Coma
• Confusion
• Delirium
• Disorientation
• Lethargy
• Stupor

Doctors and healthcare professionals use various assessments to measure and assess levels of consciousness. They use scores on these assessments to guide diagnosis and treatment decisions.

Functions of Consciousness

Consciousness has several biological and social purposes. For example, it allows us to process information, choose our actions, set priorities, learn and adapt to new information, make decisions, and more.

Consciousness is an essential state in philosophy, spirituality, and religion. All of these require self-awareness, which is impossible without consciousness.

Changes in Consciousness

Understanding different levels of consciousness can help healthcare professionals spot signs that someone might be experiencing a problem. Some of these changes occur naturally; others are the result of factors such as drugs or brain damage. Changes to consciousness also can cause changes to perception, thinking, understanding, and interpretations of the world.

For example, sudden changes in consciousness might be a sign of:

• Aneurysm
• Brain infections
• Brain tumor or injury
• Dementia or Alzheimer’s disease
• Drug use
• Epilepsy
• Heart disease
• Heatstroke
• Lack of oxygen to the brain
• Low blood sugar
• Poisoning
• Shock
• Stroke

History of Consciousness

For thousands of years, the study of human consciousness was largely the work of philosophers. The French philosopher Rene Descartes introduced the concept of mind-body dualism or the idea that while the mind and body are separate, they do interact.

Once psychology was established as a discipline separate from philosophy and biology, the study of the conscious experience became one of the first topics studied by early psychologists.

Structuralists used a process known as introspection to analyze and report conscious sensations, thoughts, and experiences. Trained observers would carefully inspect the contents of their own minds. Obviously, this was a very subjective process, but it helped inspire further research on the scientific study of consciousness.

While the focus of much of the research in psychology shifted to purely observable behaviors during the first half of the 20th century, research on human consciousness has grown tremendously since the 1950s.

Theories of Consciousness

One of the problems with the study of consciousness is the lack of a universally accepted operational definition. Descartes proposed the idea of cogito ergo sum («I think, therefore I am»), which suggested that the very act of thinking demonstrates the reality of one’s existence and consciousness.

Research on consciousness has focused on understanding the neuroscience behind our conscious experiences. Scientists have even utilized brain-scanning technology to seek out specific neurons that might be linked to different conscious events. Modern researchers have proposed two major theories of consciousness: integrated information theory and global workspace theory.

Integrated Information Theory

This approach looks at consciousness by learning more about the physical processes that underlie our conscious experiences. The theory attempts to create a measure of the integrated information that forms consciousness. The quality of an organism’s consciousness is represented by the level of integration.

Global Workspace Theory

This theory suggests that we have a memory bank from which the brain draws information to form the experience of conscious awareness. While integrated information theory focuses more on identifying whether an organism is conscious, the global workspace theory offers a much broader approach to understanding how consciousness works.

A Word From Verywell

While consciousness has intrigued philosophers and scientists for thousands of years, experts clearly have a long way to go in our understanding of the concept. Researchers continue to explore the different bases of consciousness including the physical, social, cultural, and psychological influences that contribute to our conscious awareness.

Consciousness at its simplest refers to sentience or awareness of internal or external existence. Despite centuries of analyses, definitions, explanations, and debates by philosophers and scientists, consciousness remains puzzling and controversial, being both the most familiar and the most mysterious aspect of our lives. Perhaps the only widely agreed notion about the topic is the intuition that it exists.

Beyond the problem of how to define consciousness, there are also issues of whether non-human creatures have consciousness, and if so in what form; is consciousness a biological function, is it purely material depending on the functions of the physical brain; can machines, or artificial intelligence, have consciousness; is there an evolutionary progression to consciousness such that human consciousness of a higher order; and is human consciousness a spiritual function, not just cognitive? The answers to these questions are the avenue to greater understanding of what it means to be human.

Etymology

The origin of the modern concept of consciousness is often attributed to John Locke’s Essay Concerning Human Understanding, published in 1690, where he discusses the role of consciousness in personal identity:

[C]onsciousness which is inseparable from thinking, and, as it seems to me, essential to it: it being impossible for any one to perceive without perceiving that he does perceive. When we see, hear, smell, taste, feel, meditate, or will anything, we know that we do so. … For, since consciousness always accompanies thinking, and it is that which makes every one to be what he calls self, and thereby distinguishes himself from all other thinking things, in this alone consists personal identity.^[1]

Locke’s essay influenced the eighteenth-century view of consciousness, and his definition of consciousness as «the perception of what passes in a man’s own mind» appeared in Samuel Johnson’s celebrated Dictionary originally published in 1755.^[2]
«Consciousness» (French: conscience) is also defined in the 1753 volume of Diderot and d’Alembert’s Encyclopédie, as «the opinion or internal feeling that we ourselves have from what we do.»^[3]

The earliest English language uses of «conscious» and «consciousness» date back, however, to the 1500s. The English word «conscious» originally derived from the Latin conscius (con- «together» and scio «to know»). However, the Latin word did not have the same meaning as the English word—it meant «knowing with,» in other words «having joint or common knowledge with another.»^[4] There were, however, many occurrences in Latin writings of the phrase conscius sibi, which translates literally as «knowing with oneself,» or in other words «sharing knowledge with oneself about something.» This phrase had the figurative meaning of «knowing that one knows,» as the modern English word «conscious» does. In its earliest uses in the 1500s, the English word «conscious» retained the meaning of the Latin conscius.

A related word, not to be confused with consciousness, is conscientia, which primarily means moral conscience. In the literal sense, «conscientia» means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by writers such as Cicero.^[5] Here, conscientia is the knowledge that a witness has of the deed of someone else. René Descartes (1596–1650) is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning, using conscientia the way modern speakers would use «conscience.» In Search after Truth (1701) he says «conscience or internal testimony» (conscientiâ, vel interno testimonio).^[6]

Definitions

At its simplest, consciousness refers to «sentience or awareness of internal or external existence.»^[7]
It has been defined variously in terms of «qualia,» subjectivity, the ability to experience or to feel, wakefulness, having a sense of selfhood or soul, the fact that there is something ‘that it is like’ to ‘have’ or ‘be’ it, and the executive control system of the mind.^[8] Despite the difficulty in definition, many philosophers believe that there is a broadly shared underlying intuition about what consciousness is.^[9] In sum, «Anything that we are aware of at a given moment forms part of our consciousness, making conscious experience at once the most familiar and most mysterious aspect of our lives.»^[10]

Dictionary definitions

Dictionary definitions of the word «consciousness» extend through several centuries and several associated related meanings. These have ranged from formal definitions to attempts to portray the less easily captured and more debated meanings and usage of the word.

In the Cambridge Dictionary we find consciousness defined as:

• «the state of understanding and realizing something.»^[11]

The Oxford Dictionary offers these definitions:

• «The state of being aware of and responsive to one’s surroundings»
• «A person’s awareness or perception of something» and
• «The fact of awareness by the mind of itself and the world.»^[12]

One formal definition including the range of related meanings is given in Webster’s Third New International Dictionary:

1. • «awareness or perception of an inward psychological or spiritual fact: intuitively perceived knowledge of something in one’s inner self»
   • «inward awareness of an external object, state, or fact»
   • «concerned awareness: interest, concern—often used with an attributive noun»
2. «the state or activity that is characterized by sensation, emotion, volition, or thought: mind in the broadest possible sense: something in nature that is distinguished from the physical
3. «the totality in psychology of sensations, perceptions, ideas, attitudes and feelings of which an individual or a group is aware at any given time or within a particular time span»^[13]

In philosophy

Most people have a strong intuition for the existence of what they refer to as consciousness. However, philosophers differ from non-philosophers in their intuitions about what consciousness is.^[14]

While non-philosophers would find familiar the elements in the dictionary definitions above, philosophers approach the term somewhat differently. For example, the Routledge Encyclopedia of Philosophy in 1998 contained the following more complex definition of consciousness:

Philosophers have used the term ‘consciousness’ for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience… Something within one’s mind is ‘introspectively conscious’ just in case one introspects it (or is poised to do so). Introspection is often thought to deliver one’s primary knowledge of one’s mental life. An experience or other mental entity is ‘phenomenally conscious’ just in case there is ‘something it is like’ for one to have it. The clearest examples are: perceptual experience, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one’s own actions or perceptions; and streams of thought, as in the experience of thinking ‘in words’ or ‘in images.’ Introspection and phenomenality seem independent, or dissociable, although this is controversial.^[15]

In a more skeptical definition, Stuart Sutherland exemplified some of the difficulties in fully ascertaining all of its cognate meanings in his entry for the 1989 version of the Macmillan Dictionary of Psychology:

Consciousness—The having of perceptions, thoughts, and feelings; awareness. The term is impossible to define except in terms that are unintelligible without a grasp of what consciousness means. Many fall into the trap of equating consciousness with self-consciousness—to be conscious it is only necessary to be aware of the external world. Consciousness is a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it has evolved. Nothing worth reading has been written on it.^[16]

Generally, philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness.^[16]

Philosophical issues

Western philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. These issues remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively. Some basic questions include: whether consciousness is the same kind of thing as matter; whether it may ever be possible for computing machines like computers or robots to be conscious; how consciousness relates to language; how consciousness as Being relates to the world of experience; the role of the self in experience; and whether the concept is fundamentally coherent.

Mind–body problem

Mental processes (such as consciousness) and physical processes (such as brain events) seem to be correlated. However, the specific nature of the connection is unknown. The philosophy of mind has given rise to many stances regarding consciousness. In particular, the two major schools of thought regarding the nature of the mind and the body, Dualism and monism, are directly related to the nature of consciousness.

Dualism, originally proposed by René Descartes, is the position that mind and body are separate from each other.^[17] Dualist theories maintain Descartes’ rigid distinction between the realm of thought, where consciousness resides, and the realm of matter, but give different answers for how the two realms relate to each other. The two main types of dualism are substance dualism, which holds that the mind is formed of a distinct type of substance not governed by the laws of physics, and property dualism, which holds that the laws of physics are universally valid but cannot be used to explain the mind.

Monism, on the other hand, rejects the dualist separation and maintains that mind and body are, at the most fundamental level, the same realm of being of which consciousness and matter are both aspects. This can mean that both are mental, such that only thought or experience truly exists and matter is merely an illusion (idealism); or that everything is material (physicalism), which holds that the mind consists of matter organized in a particular way; and neutral monism, which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them.

These two schools of dualism and monism have different conceptions of consciousness, with arguments for and against on both sides. This has led a number of philosophers to reject the dualism/monism dichotomy. Gilbert Ryle, for example, argued that the traditional understanding of consciousness depends on a Cartesian dualist outlook that improperly distinguishes between mind and body, or between mind and world. Thus, by speaking of «consciousness» we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.^[18]

David Chalmers formulated what he calls the «hard problem of consciousness,» which distinguishes between «easy» (cognitive) problems of consciousness, such as explaining object discrimination or verbal reports, and the single hard problem, which could be stated «why does the feeling which accompanies awareness of sensory information exist at all?» The easy problems are at least theoretically answerable via the dominant monistic philosophy of mind: physicalism. The hard problem, on the other hand, is not. He argues for an «explanatory gap» from the objective to the subjective mental experience, a view which he characterizes as «naturalistic dualism»: naturalistic because he believes mental states are caused by physical systems (brains); dualist because he believes mental states are ontologically distinct from and not reducible to physical systems.^[19]

Problem of other minds

Many philosophers consider experience to be the essence of consciousness, and believe that experience can fully be known only from the inside, subjectively. But if consciousness is subjective and not visible from the outside, why do the vast majority of people believe that other people are conscious, but rocks and trees are not? This is what is known as the problem of other minds.^[20]

The most commonly given answer is that we attribute consciousness to other people because we see that they resemble us in appearance and behavior. We reason that if they look like us and act like us, they must be like us in other ways, including having experiences of the sort that we do.^[20] More broadly, philosophers who do not accept the possibility of philosophical zombies, entities that lack consciousness but otherwise appear and behave as humans,^[21] generally believe that consciousness is reflected in behavior (including verbal behavior), and that we attribute consciousness on the basis of behavior. In other words, we attribute experiences to people because of what they can do, including the fact that they can tell us about their experiences.

Animal consciousness

The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because non-human animals, lacking the ability to express human language, cannot tell us about their experiences. Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Most people have a strong intuition that some animals, such as cats and dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious.

Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled What Is it Like to Be a Bat?. He stated that an organism is conscious «if and only if there is something that it is like to be that organism—something it is like for the organism»; and he argued that no matter how much we know about an animal’s brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself.^[22]

On July 7, 2012, eminent scientists from different branches of neuroscience gathered at the University of Cambridge to celebrate the Francis Crick Memorial Conference, which deals with consciousness in humans and pre-linguistic consciousness in nonhuman animals. After the conference, they signed in the presence of Stephen Hawking the Cambridge Declaration on Consciousness which concluded that consciousness exists in animals:

The absence of a neocortex does not appear to preclude an organism from experiencing affective states. Convergent evidence indicates that non-human animals have the neuroanatomical, neurochemical, and neurophysiological substrates of conscious states along with the capacity to exhibit intentional behaviors. Consequently, the weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Non-human animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates.^[23]

Artifact consciousness

The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the Golem, a magically animated homunculus built of clay.^[24] However, the possibility of actually constructing a conscious machine was probably first discussed by Ada Lovelace, in a set of notes written in 1842 about the Analytical Engine invented by Charles Babbage, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a human-like way:

It is desirable to guard against the possibility of exaggerated ideas that might arise as to the powers of the Analytical Engine. … The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its province is to assist us in making available what we are already acquainted with.^[25]

One of the most influential contributions to this question was an essay written in 1950 by pioneering computer scientist Alan Turing in which he stated that the question «Can machines think?» is meaningless. Instead he proposed «the imitation game,» which has become known as the Turing test.^[26] To pass the test, a computer must be able to imitate a human well enough to fool interrogators.^[27]

The Turing test is commonly cited in discussions of artificial intelligence as a proposed criterion for machine consciousness, provoking a great deal of philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious.^[28] On the other hand, David Chalmers argues that a philosophical zombie, an imaginary entity that is physically indistinguishable from a human being and behaves like a human being in every way but nevertheless lacks consciousness, could pass the test. By definition, such an entity is not conscious.^[19]

In a lively exchange over what has come to be referred to as «the Chinese room argument,» John Searle sought to refute the claim of proponents of «strong artificial intelligence (AI)» that a computer program can be conscious, though agreed with advocates of «weak AI» that computer programs can be formatted to «simulate» conscious states. He argued that consciousness has subjective, first-person causal powers by being essentially intentional due to the way human brains function biologically. Conscious persons can perform computations, but consciousness is not inherently computational the way computer programs are.

To illustrate the difference, Searle described a thought experiment involving a room with one monolingual English speaker, a book that designates a combination of Chinese symbols to be output paired with Chinese symbol input, and boxes filled with Chinese symbols. In this case, the English speaker is acting as a computer and the rule book as a program. Searle argues that with such a machine, he would be able to process the inputs to outputs perfectly without having any understanding of Chinese, nor having any idea what the questions and answers could possibly mean. On the other hand, if the experiment were done in English, the person would be able to take questions and give answers without any algorithms for English questions, and he would be effectively aware of what was being said and the purposes it might serve. The person would pass the Turing test of answering the questions in both languages, but would be conscious of what he is doing only when the language is English. Put another way, computer programs can pass the Turing test for processing the syntax of a language, but syntax cannot lead to semantic meaning in the way strong AI advocates hope.^[29]

Searle did not clarify what was needed to make the leap from using syntactic rules to understanding of meaning, and at the time of his initial writing computers were limited to computational information processing. Since then, intelligent virtual assistants, such as Apple’ Siri, have become commonplace. While they are capable of answering a number of questions, they have not yet reached the human standard of conversation. IBM claims that Watson “knows what it knows, and knows what it does not know,” and indeed was able to beat human champions on the television game show Jeopardy, a feat that relies heavily on language abilities and inference. However, as John Searle pointed out, this is not the same as being aware of what it meant to win the game show, understanding that it was a game, and that it won.^[30]

The best computers have been shown only to simulate human cognition; they have not been shown to demonstrate consciousness; nor have they put an end to the question of whether there is a biological basis to consciousness.^[31]

Phenomenology

Phenomenology is a method of inquiry that attempts to examine the structure of consciousness in its own right, putting aside problems regarding the relationship of consciousness to the physical world. This approach was first proposed by the philosopher Edmund Husserl, and later elaborated by other philosophers and scientists.^[32]

Phenomenology is, in Husserl’s formulation, the study of experience and the ways in which things present themselves in and through experience. Taking its starting point from the first-person perspective, phenomenology attempts to describe the essential features or structures of a given experience or any experience in general. One of the central structures of any experience is its intentionality, or its being directed toward some object or state of affairs. The theory of intentionality, the central theme of phenomenology, maintains that all experience necessarily has this object-relatedness and thus one of the catch phrases of phenomenology is “all consciousness is consciousness of.”

Husserl’s original concept gave rise to two distinct lines of inquiry, in philosophy and in psychology. In philosophy, phenomenology has largely been devoted to fundamental metaphysical questions, such as the nature of intentionality («aboutness»). In psychology, phenomenology has meant attempting to investigate consciousness using the method of introspection, which means looking into one’s own mind and reporting what one observes. This method fell into disrepute in the early twentieth century because of grave doubts about its reliability, but has been rehabilitated to some degree, especially when used in combination with techniques for examining brain activity.^[33]

Introspectively, the world of conscious experience seems to have considerable structure. Immanuel Kant asserted that the world as we perceive it is organized according to a set of fundamental «intuitions,» which include ‘object’ (we perceive the world as a set of distinct things); ‘shape’; ‘quality’ (color, warmth, etc.); ‘space’ (distance, direction, and location); and ‘time’. Some of these constructs, such as space and time, correspond to the way the world is structured by the laws of physics; for others the correspondence is not as clear. Understanding the physical basis of qualities, such as redness or pain, has been particularly challenging. Some philosophers have argued that it is intrinsically unsolvable, because qualities («qualia») are ineffable; that is, they are «raw feels,» incapable of being analyzed into component processes.^[34]

Scientific study

Since the dawn of Newtonian science with its vision of simple mechanical principles governing the entire universe, it has been tempting to explain consciousness in purely physical terms. The first influential writer to propose such an idea explicitly was Julien Offray de La Mettrie, in his book Man a Machine (L’homme machine), which dealt with the notion only in the abstract.^[35]

Broadly viewed, such scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In both cases, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.^[36]

Consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology, neuropsychology, and neuroscience. The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness. The majority of experimental studies assess consciousness in humans by asking subjects for a verbal report of their experiences (such as, «tell me if you notice anything when I do this»). Issues of interest include phenomena such as subliminal perception, blindsight, denial of impairment, and altered states of consciousness produced by alcohol and other drugs or meditative techniques.

Measurement

Experimental research on consciousness presents special difficulties due to the lack of a universally accepted operational definition. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion used is verbal report. In other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness.^[37] For example, subjects who stare continuously at a Necker cube usually report that they experience it «flipping» between two 3D configurations, even though the stimulus itself remains the same.

Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.^[38] If verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected.^[39] Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language. This approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. A third issue is that those who dispute the validity of the Turing test may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness.^[19]

Although verbal report is in practice the «gold standard» for ascribing consciousness, it is not the only possible criterion.^[38] In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity, and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness.^[40]

Another approach applies specifically to the study of self-awareness, that is, the ability to distinguish oneself from others. In the 1970s Gordon Gallup developed an operational test for self-awareness, known as the mirror test. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual’s forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves.^[41] Humans (older than 18 months) and other great apes, bottlenose dolphins, killer whales, pigeons, European magpies and elephants have all been observed to pass this test.

Neural correlates

In neuroscience, a great deal of effort has gone into investigating how the perceived world of conscious awareness is constructed inside the brain. This is done by examining the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the neural correlates of consciousness. The hope is to find activity in a particular part of the brain, or a particular pattern of global brain activity, which will be strongly predictive of conscious awareness. Such studies use brain imaging techniques, such as EEG and fMRI, for physical measures of brain activity.^[36]

The process of constructing conscious awareness is generally thought to involve two primary mechanisms: (1) hierarchical processing of sensory inputs, and (2) memory. Signals arising from sensory organs are transmitted to the brain and then processed in a series of stages, which extract multiple types of information from the raw input. In the visual system, for example, sensory signals from the eyes are transmitted to the thalamus and then to the primary visual cortex. Studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness. It is possible for subjects to report a lack of awareness even when areas such as the primary visual cortex show clear electrical responses to a stimulus.^[36] Higher brain areas, especially the prefrontal cortex, which is involved in a range of higher cognitive functions collectively known as executive functions, then extract features such as three-dimensional structure, shape, color, and motion.^[42] Memory comes into play in at least two ways during this activity. First, it allows sensory information to be evaluated in the context of previous experience. Second, and even more importantly, working memory allows information to be integrated over time so that it can generate a stable representation of the world.

Biological function and evolution

Opinions are divided as to where in biological evolution consciousness emerged and about whether or not consciousness has any survival value. Even among writers who consider consciousness to be well-defined, there is widespread dispute about which animals other than humans can be said to possess it.^[43]

It has been argued that consciousness emerged (i) exclusively with the first humans, (ii) exclusively with the first mammals, (iii) independently in mammals and birds, or (iv) with the first reptiles.^[44] Other suggestions include the appearance of consciousness in the first animals with nervous systems or early vertebrates in the Cambrian over 500 million years ago, or a gradual evolution of consciousness.^[45] Another viewpoint distinguishes between primary consciousness, which is a trait shared by humans and non-human animals, and higher-order consciousness which appears only in humans along with their capacity for language.^[46] Supporting this distinction, several scholars including Pinker, Chomsky, and Luria have indicated the importance of the emergence of human language as a regulative mechanism of learning and memory in the context of the development of higher-order consciousness. Each of these evolutionary scenarios raises the question of the possible survival value of consciousness.

Some writers have argued that consciousness can be viewed from the standpoint of evolutionary biology as an adaptation that increases fitness. For example, consciousness allows an individual to make distinctions between appearance and reality.^[47] This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (that water in the distance may be a mirage, for instance) and behave accordingly. It could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends.

William James argued that if the preservation and development of consciousness occurs in biological evolution, it is plausible that consciousness has not only been influenced by neural processes, but has had a survival value itself; and it could only have had this if it had been efficacious: «Consciousness … has been slowly evolved in the animal series, and resembles in this all organs that have a use.»^[48] A similar evolutionary argument was presented by Karl Popper.^[49]

Medical aspects

The medical approach to consciousness is practically oriented. It derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. Whereas the philosophical approach to consciousness focuses on its fundamental nature and its contents, the medical approach focuses on the level of consciousness, ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end.^[50]

Assessment

In medicine, consciousness is assessed by observing a patient’s arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli.^[34] The degree of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale, which is composed of three tests: eye, verbal, and motor responses. Scores range from 3 to 15, with a score of 3 to 8 indicating coma, and 15 indicating full consciousness.

Issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted.

Disorders of consciousness

Medical conditions that inhibit consciousness are considered disorders of consciousness. This category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma. Finally, brain death results in an irreversible disruption of consciousness.

While other conditions may cause a moderate deterioration (for example, dementia and delirium) or transient interruption (such as grand mal and petit mal seizures) of consciousness, they are not included in this category.

Disorder	Description
Locked-in syndrome	The patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy.
Minimally conscious state	The patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior.
Persistent vegetative state	The patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior.
Chronic coma	The patient lacks awareness and sleep-wake cycles and only displays reflexive behavior.
Brain death	The patient lacks awareness, sleep-wake cycles, and brain-mediated reflexive behavior.

Altered states of consciousness

There are some brain states in which consciousness seems to be absent, including dreamless sleep, coma, and death. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage. Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image, and changes in meaning or significance.

The two most widely accepted altered states are sleep and dreaming. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may be interrupted by bizarre or fantastic intrusions. Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory, usually disappearing in seconds in the non-dream state, and in minutes after awakening from a dream unless actively refreshed.^[51]

Studies of altered states of consciousness by Charles Tart in the 1960s and 1970s led to the possible identification of a number of component processes of consciousness which can be altered by drugs or other manipulations. These include exteroception (sensing the external world); interoception (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment.^[52]

A variety of psychoactive drugs, including alcohol, have notable effects on consciousness. These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, empathogens–entactogens such as MDMA («Ecstasy»), or most notably by the class of drugs known as psychedelics. LSD, mescaline, psilocybin, Dimethyltryptamine, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality.

Research into physiological changes in yogis and people who practice various techniques of meditation suggests brain waves during meditation differ from those corresponding to ordinary relaxation. It has been disputed, however, whether these are physiologically distinct states of consciousness.^[53]

Stream of consciousness

William James is usually credited with popularizing the idea that human consciousness flows like a stream. According to James, the «stream of thought» is governed by five characteristics:

1. Every thought tends to be part of a personal consciousness.
2. Within each personal consciousness thought is always changing.
3. Within each personal consciousness thought is sensibly continuous.
4. It always appears to deal with objects independent of itself.
5. It is interested in some parts of these objects to the exclusion of others.^[54]

A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or «mental continuum.» Buddhist teachings describe consciousness as manifesting moment to moment as sense impressions and mental phenomena that are continuously changing. The moment-by-moment manifestation of the mind-stream is said to happen in every person all the time. The purpose of the Buddhist practice of mindfulness is to understand the inherent nature of the consciousness and its characteristics.^[55]

In the west, the primary impact of the idea has been on literature rather than science. Stream of consciousness as a narrative mode means writing in a way that attempts to portray the moment-to-moment thoughts and experiences of a character. This technique reached its fullest development in the novels of James Joyce and Virginia Woolf, although it has also been used by many other noted writers.^[56]

Spiritual approaches

To most philosophers, the word «consciousness» connotes the relationship between the mind and the world. To writers on spiritual or religious topics, it frequently connotes the relationship between the mind and God, or the relationship between the mind and deeper truths that are thought to be more fundamental than the physical world. The spiritual approach distinguishes various levels of consciousness, forming a spectrum with ordinary awareness at one end, and more profound types of awareness at higher levels.^[57]

Notes

References

ISBN links support NWE through referral fees

• Baars, Bernard J. A Cognitive Theory of Consciousness. Cambridge University Press, 1993. ISBN 978-0521427432
• Bennett, M.R., and P.M.S. Hacker. Philosophical Foundations of Neuroscience. Wiley-Blackwell, 2003. ISBN 978-1405108386
• Block, Ned, Owen J. Flanagan, and Guven Guzeldere (eds.). The Nature of Consciousness: Philosophical Debates. A Bradford Book, 1997. ISBN 978-0262522106
• Budiansky, Stephen. If a Lion Could Talk: Animal Intelligence and the Evolution of Consciousness. Free Press, 2015. ISBN 978-1501142741
• Carruthers, Peter. Phenomenal Consciousness: A Naturalistic Theory. Cambridge University Press, 2000. ISBN 978-0521781732
• Cassin, Barbara, Emily Apter, Jacques Lezra, and Michael Wood (eds.). Dictionary of Untranslatables: A Philosophical Lexicon. Princeton University Press, 2014. ISBN 978-0691138701
• Chalmers, David J. The Conscious Mind. Oxford University Press, 1997. ISBN 978-0195117899
• Chalmers, David J. The Character of Consciousness. Oxford University Press, 2010. ISBN 978-0195311112
• Craig, Edward (ed.). Routledge Encyclopedia of Philosophy. Routledge, 1998. ISBN 978-0415073103
• Descartes, René, John Cottingham (trans.). Meditations on First Philosophy. Cambridge University Press, 2017. ISBN 978-1107665736
• Edelman, Gerald, and Giulio Tononi. A Universe Of Consciousness: How Matter Becomes Imagination. Basic Books, 2001. ISBN 978-0465013777
• Gove, Philip Babcock (ed.). Webster’s Third New International Dictionary of the English Language. Merriam-Webster, 1993. ISBN 978-0877792017
• Griffin, Donald R. Animal Minds. University Of Chicago Press, 1994. ISBN 978-0226308647
• Heinämaa, Sara, Vili Lähteenmäki, and Pauliina Remes (eds.). Consciousness: From Perception to Reflection in the History of Philosophy. Springer, 2007. ISBN 978-1402060816
• Honderich, Ted (ed.). The Oxford Companion to Philosophy. Oxford University Press, 2005. ISBN 978-0199264797
• Humphrey, Robert. Stream of Consciousness In the Modern Novel. University of California Press, 1972. ISBN 978-0520005853
• Hyslop, Alec. Other Minds. Springer, 2010. ISBN 978-9048144976
• Idel, Moshe. Golem: Jewish Magical and Mystical Traditions on the Artificial Anthropoid. KTAV Publishing House, 2019. ISBN 978-1602803527
• Jack, Anthony, and Andreas Roepstorff (eds.). Trusting the Subject? Volume 1. Imprint Academic, 2003. ISBN 978-0907845560
• James, William. The Principles of Psychology, Vol. 1. Dover Publications, 1950. ISBN 978-0486203812
• Johnson, Samuel. A Dictionary of the English Language. Forgotten Books, 2016. ISBN 978-1333070120
• Koch, Christof. The Quest for Consciousness: A Neurobiological Approach. Roberts & Co, 2004. ISBN 978-0974707709
• La Mettrie, Julien Offray de. Machine Man and Other Writings. Cambridge University Press, 1996. ISBN 978-0521472586
• Laureys, Steven (ed.). The Boundaries of Consciousness: Neurobiology and Neuropathology. Elsevier Science, 2005 ISBN 978-0444518514
• Laureys, Steven, and Giulio Tononi (eds.). The Neurology of Consciousness: Cognitive Neuroscience and Neuropathology. Academic Press, 2008. ISBN 978-0123741684
• Lewis, C.S. Studies in Words. Cambridge University Press, 2013. ISBN 978-1107688650
• Liljenström, Hans, and Peter Århem (eds.). Consciousness Transitions: Phylogenetic, Ontogenetic and Physiological Aspects. Elsevier Science, 2007. ISBN 978-0444529770
• Locke, John. An Essay Concerning Human Understanding. Wordsworth Editions Ltd, 2014. ISBN 978-1840227321
• Marcel, A.J., and E. Bisiach (eds.). Consciousness in Contemporary Science. Clarendon Press, 1992. ISBN 978-0198522379
• Murphy, Michael, Steven Donovan, et al. The Physical and Psychological Effects of Meditation. Institute of Noetic Sciences, 1997. ISBN 978-0943951362
• Nagel, Thomas. Mortal Questions. Cambridge University Press, 2012. ISBN 1107604710
• Pace-Schott, Edward F., Mark Solms, Mark Blagrove, and Stevan Harnad (eds.). Sleep and Dreaming: Scientific Advances and Reconsiderations. Cambridge University Press, 2003. ISBN 978-0521008693
• Popper, Karl, and John C. Eccles. The Self and Its Brain: An Argument for Interactionism. Routledge, 1984. ISBN 978-0415058988
• Ryle, Gilbert. The Concept of Mind. University of Chicago Press, 2000. ISBN 978-0226732961
• Schneider, Susan, and Max Velmans (eds.). The Blackwell Companion to Consciousness. Wiley-Blackwell, 2017. ISBN 978-0470674079
• Shieber, Stuart. The Turing Test: Verbal Behavior as the Hallmark of Intelligence. MIT Press, 2004. ISBN 978-0262692939
• Sutherland, Stuart. Macmillan Dictionary of Psychology. Palgrave Macmillan, 1989. ISBN 978-0333388297
• Tart, Charles. States of Consciousness. iUniverse, 2001. ISBN 978-0595151967
• Wolter, Doris (ed.). Losing the Clouds, Gaining the Sky: Buddhism and the Natural Mind. Wisdom Publications, 2007. ISBN 978-0861713592
• Wilber, Ken. The Spectrum of Consciousness. Quest Books, 1993. ISBN 978-0835606950

External links

All links retrieved July 14, 2020.

• Consciousness Stanford Encyclopedia of Philosophy
• Consciousness Internet Encyclopedia of Philosophy
• What Is Consciousness?

Assessment |
Biopsychology |
Comparative |
Cognitive |
Developmental |
Language |
Individual differences |
Personality |
Philosophy |
Social |
Methods |
Statistics |
Clinical |
Educational |
Industrial |
Professional items |
World psychology |

Philosophy Index:
Aesthetics ·
Epistemology ·
Ethics ·
Logic ·
Metaphysics ·
Consciousness ·
Philosophy of Language ·
Philosophy of Mind ·
Philosophy of Science ·
Social and Political philosophy ·
Philosophies ·
Philosophers ·
List of lists

---

This article is in need of attention from a psychologist/academic expert on the subject.
Please help recruit one, or improve this page yourself if you are qualified.
This banner appears on articles that are weak and whose contents should be approached with academic caution.

Consciousness is the quality or state of being aware of an external object or something within oneself.^[1][2] It has been defined as: sentience, awareness, subjectivity, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind.^[3] Despite the difficulty in definition, many philosophers believe that there is a broadly shared underlying intuition about what consciousness is.^[4] As Max Velmans and Susan Schneider wrote in The Blackwell Companion to Consciousness: «Anything that we are aware of at a given moment forms part of our consciousness, making conscious experience at once the most familiar and most mysterious aspect of our lives.»^[5]

Philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and pin down its essential properties. Issues of concern in the philosophy of consciousness include whether the concept is fundamentally valid; whether consciousness can ever be explained mechanistically; whether non-human consciousness exists and if so how it can be recognized; how consciousness relates to language; whether consciousness can be understood in a way that does not require a dualistic distinction between mental and physical states or properties; and whether it may ever be possible for computers or robots to be conscious.

At one time consciousness was viewed with skepticism by many scientists, but in recent years it has become a significant topic of research in psychology and neuroscience. The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness. The majority of experimental studies assess consciousness by asking human subjects for a verbal report of their experiences (e.g., «tell me if you notice anything when I do this»). Issues of interest include phenomena such as subliminal perception, blindsight, denial of impairment, and altered states of consciousness produced by psychoactive drugs or spiritual or meditative techniques.

In medicine, consciousness is assessed by observing a patient’s arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli.^[6] Issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted.^[7]

Etymology

«Consciousness» derives from Latin conscientia which primarily means moral conscience. In the literal sense, «conscientia» (or «con scientia») means knowledge-with, that is, shared knowledge. The word first appears in Latin juridic texts by writers such as Cicero. Here, conscientia is the knowledge that a witness has of the deed of someone else. In Christian theology, conscience stands for the moral conscience in which our actions and intentions are registered and which is only fully known to God. Medieval writers such as Thomas Aquinas describe the conscientia as the act by which we apply practical and moral knowledge to our own actions.^[8]
René Descartes has been said to be the first philosopher to use «conscientia» in a way that does not seem to fit this traditional meaning, and, as a consequence, the translators of his writings in other languages like French and English coined new words in order to denote merely psychological consciousness. These are, for instance, conscience, and Bewusstsein.^[9]
However, it has also been argued that John Locke was in fact the first one to use the modern meaning of consciousness in his Essay Concerning Human Understanding, although it remains closely intertwined with moral conscience (I may be held morally responsible only for the act of which I am conscious of having achieved; and my personal identity — my self — goes as far as my consciousness extends itself). The modern sense of «consciousness» was therefore first found not in Descartes’ work — who sometimes used the word in a modern sense, but did not distinguish it as much as Locke would do -, but in Locke’s text. The contemporary sense of the word (consciousness associated to the idea of personal identity, which is assured by the repeated consciousness of oneself) was therefore introduced by Locke; but the word «conscience» itself was coined by Pierre Costes, French translator of Locke. Henceforth, the modern sense first appeared in Locke’s works, but the word itself first appeared in the French language.^[10]
Locke’s influence upon the concept can be found in Samuel Johnson‘s celebrated Dictionary, in which Johnson abstains from offering a definition of «consciousness,» choosing instead to simply quote Locke.

Philosophical approaches

File:RobertFuddBewusstsein17Jh.png

Main article: Philosophy of mind

There are many philosophical stances on consciousness, including: behaviorism, dualism, idealism, functionalism, reflexive monism, phenomenalism, phenomenology and intentionality, physicalism, emergentism, mysticism, personal identity etc.

Phenomenal and access consciousness

Phenomenal consciousness (P-consciousness) is simply experience; it is moving, coloured forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. These experiences, considered independently of any impact on behavior, are called qualia. The hard problem of consciousness was formulated by Chalmers in 1996, dealing with the issue of «how to explain a state of phenomenal consciousness in terms of its neurological basis» (Block 2004).

Access consciousness (A-consciousness) is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. So, when we perceive, information about what we perceive is often access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past (e.g., something that we learned) is often access conscious; and so on. Chalmers thinks that access consciousness is less mysterious than phenomenal consciousness, so that it is held to pose one of the easy problems of consciousness. Dennett denies that there is a «hard problem», asserting that the totality of consciousness can be understood in terms of impact on behavior, as studied through heterophenomenology. There have been numerous approaches to the processes that act on conscious experience from instant to instant. Philosophers who have explored this problem include Gerald Edelman, Edmund Husserl and Daniel Dennett. Daniel Dennett (1988) suggests that what people think of as phenomenal consciousness, such as qualia, are judgements and consequent behaviour. He extends this analysis (Dennett, 1996) by arguing that phenomenal consciousness can be explained in terms of access consciousness, denying the existence of qualia, hence denying the existence of a «hard problem.»

Events that occur in the mind or brain that are not within phenomenal or access consciousness are known as subconscious events.

The description and location of phenomenal consciousness

Philosophers have investigated phenomenal consciousness for centuries. René Descartes, who arrived upon the famous dictum ‘cogito ergo sum‘, wrote Meditations on First Philosophy in the seventeenth century, containing extensive descriptions of what it is to be conscious. Descartes described conscious experience as ideas such as imaginings and perceptions laid out in space and time that are viewed from a point, and appearing as a result of some quality (qualia) such as color, smell, and so on; this notion of interchangeability between the terms ‘idea’ and ‘imaginings’ can cause confusion among modern readers.

Like Aristotle Descartes defines ideas as extended things, as in this excerpt from his Treatise on Man:

Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas — but only those which are traced in the spirits on the surface of gland H [where the seat of the imagination and the ‘common sense’ is located]. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.

Thus Descartes does not identify mental ideas or ‘qualia’ with activity within the sense organs, or even with brain activity, but rather with interaction between body and the ‘rational soul’, through the mediating ‘gland H’. This organ is now known as the pineal gland. Descartes notes that, anatomically, while the human brain consists of two symmetrical hemispheres the pineal gland, which lies close to the brain’s centre, is singular. Thus he extrapolated from this that it was the mediator between body and soul.

Other philosophers agreed with Descartes to varying degrees, such as Nicolas Malebranche, Thomas Reid, John Locke, David Hume and Immanuel Kant. Malebranche, for example, agreed with Descartes that the human being was composed of two elements, body and mind, and that conscious experience resided in the latter. He did, however, disagree with Descartes as to the ease with which we might become aware of our mental constitution, stating ‘I am not my own light unto myself’. David Hume and Immanuel Kant also differ from Descartes, in that they avoid mentioning a place from which experience is viewed (see «Further reading» below); certainly, few if any modern philosophers have identified the pineal gland as the seat of dualist interaction.

The extension of things in time was considered in more detail by Kant and James. Kant wrote that «only on the presupposition of time can we represent to ourselves a number of things as existing at one and the same time [simultaneously] or at different times [successively].» William James stressed the extension of experience in time and said that time is «the short duration of which we are immediately and incessantly sensible.»

When we look around a room or have a dream, things are laid out in space and time and viewed as if from a point. However, when philosophers and scientists consider the location of the form and contents of this phenomenal consciousness, there are fierce disagreements. As an example, Descartes proposed that the contents are brain activity seen by a non-physical place without extension (the Res Cogitans), which, in Meditations on First Philosophy, he identified as the soul. This idea is known as Cartesian Dualism. Another example is found in the work of Thomas Reid who thought the contents of consciousness are the world itself, which becomes conscious experience in some way. This concept is a type of Direct realism. The precise physical substrate of conscious experience in the world, such as photons, quantum fields, etc. is usually not specified.

Other philosophers, such as George Berkeley, have proposed that the contents of consciousness are an aspect of minds and do not necessarily involve matter at all. This is a type of Idealism. Yet others, such as Leibniz, have considered that each point in the universe is endowed with conscious content. This is a form of Panpsychism. Panpsychism is the belief that all matter, including rocks for example, is sentient or conscious. The concept of the things in conscious experience being impressions in the brain is a type of representationalism, and representationalism is a form of indirect realism.

It is sometimes held that consciousness emerges from the complexity of brain processing. The general label ’emergence’ applies to new phenomena that emerge from a physical basis without the connection between the two explicitly specified.

Some theorists hold that phenomenal consciousness poses an explanatory gap. Colin McGinn takes the New Mysterianism position that it can’t be solved, and Chalmers criticizes purely physical accounts of mental experiences based on the idea that philosophical zombies are logically possible and supports property dualism. But others have proposed speculative scientific theories to explain the explanatory gap, such as Quantum mind, space-time theories of consciousness, reflexive monism, and Electromagnetic theories of consciousness to explain the correspondence between brain activity and experience.

Parapsychologists sometimes appeal to the unproven concepts of psychokinesis or telepathy to support the dualistic belief that consciousness is not confined to the brain.

Types of consciousness

Many philosophers have argued that consciousness is a unitary concept that is understood intuitively by the majority of people in spite of the difficulty in defining it.^[11] Others, though, have argued that the level of disagreement about the meaning of the word indicates that it either means different things to different people (for instance, the objective versus subjective aspects of consciousness), or else is an umbrella term encompassing a variety of distinct meanings with no simple element in common.^[12]

Ned Block proposed a distinction between two types of consciousness that he called phenomenal (P-consciousness) and access (A-consciousness).^[13] P-consciousness, according to Block, is simply raw experience: it is moving, colored forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. These experiences, considered independently of any impact on behavior, are called qualia. A-consciousness, on the other hand, is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. So, when we perceive, information about what we perceive is access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past is access conscious, and so on. Although some philosophers, such as Daniel Dennett, have disputed the validity of this distinction,^[14] others have broadly accepted it. David Chalmers has argued that A-consciousness can in principle be understood in mechanistic terms, but that understanding P-consciousness is much more challenging: he calls this the hard problem of consciousness.^[15]

Some philosophers believe that Block’s two types of consciousness are not the end of the story. William Lycan, for example, argued in his book Consciousness and Experience that at least eight clearly distinct types of consciousness can be identified (organism consciousness; control consciousness; consciousness of; state/event consciousness; reportability; introspective consciousness; subjective consciousness; self-consciousness)—and that even this list omits several more obscure forms.^[16]

Mind–body problem

Main article: Mind–body problem

The first influential philosopher to discuss this question specifically was Descartes and the answer he gave is known as Cartesian dualism. Descartes proposed that consciousness resides within an immaterial domain he called res cogitans (the realm of thought), in contrast to the domain of material things which he called res extensa (the realm of extension).^[17] He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.^[18]

Although it is widely accepted that Descartes explained the problem cogently, few later philosophers have been happy with his solution, and his ideas about the pineal gland have especially been ridiculed.^[19] Alternative solutions, however, have been very diverse. They can be divided broadly into two categories: dualist solutions that maintain Descartes’ rigid distinction between the realm of consciousness and the realm of matter but give different answers for how the two realms relate to each other; and monist solutions that maintain that there is really only one realm of being, of which consciousness and matter are both aspects. Each of these categories itself contains numerous variants. The two main types of dualism are substance dualism (which holds that the mind is formed of a distinct type of substance not governed by the laws of physics) and property dualism (which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of monism are physicalism (which holds that the mind consists of matter organized in a particular way), idealism (which holds that only thought truly exists and matter is merely an illusion), and neutral monism (which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them). There are also, however, a large number of idiosyncratic theories that cannot cleanly be assigned to any of these camps.^[20]

Since the dawn of Newtonian science with its vision of simple mechanical principles governing the entire universe, some philosophers have been tempted by the idea that consciousness could be explained in purely physical terms. The first influential writer to propose such an idea explicitly was Julien Offray de La Mettrie, in his book Man a Machine (L’homme machine). His arguments, however, were very abstract.^[21] The most influential modern physical theories of consciousness are based on psychology and neuroscience. Theories proposed by neuroscientists such as Gerald Edelman^[22] and Antonio Damasio,^[23] and by philosophers such as Daniel Dennett,^[24] seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as Christof Koch,^[25] have explored the neural basis of consciousness without attempting to frame all-encompassing global theories. At the same time, computer scientists working in the field of Artificial Intelligence have pursued the goal of creating digital computer programs that can simulate or embody consciousness.^[26]

A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, but that quantum theory provides the missing ingredients. Several theorists have therefore proposed quantum mind (QM) theories of consciousness.^[27] Notable theories falling into this category include the Holonomic brain theory of Karl Pribram and David Bohm, and the Orch-OR theory formulated by Stuart Hameroff and Roger Penrose. Some of these QM theories offer descriptions of phenomenal consciousness, as well as QM interpretations of access consciousness. None of the quantum mechanical theories has been confirmed by experiment. Recent papers by Guerreshi, G., Cia, J., Popescu, S. and Briegel, H.^[28] could falsify proposals such as those of Hameroff which rely on quantum entanglement in protein. At the present time many scientists and philosophers consider the arguments for an important role of quantum phenomena to be unconvincing.^[29]

Apart from the general question of the «hard problem» of consciousness, roughly speaking, the question of how mental experience arises from a physical basis,^[30] a more specialized question is how to square the subjective notion that we are in control of our decisions (at least in some small measure) with the customary view of causality that subsequent events are caused by prior events. The topic of free will is the philosophical and scientific examination of this conundrum.

Problem of other minds

Many philosophers consider experience to be the essence of consciousness, and believe that experience can only fully be known from the inside, subjectively. But if consciousness is subjective and not visible from the outside, why do the vast majority of people believe that other people are conscious, but rocks and trees are not?^[31] This is called the problem of other minds.^[32] It is particularly acute for people who believe in the possibility of philosophical zombies, that is, people who think it is possible in principle to have an entity that is physically indistinguishable from a human being and behaves like a human being in every way but nevertheless lacks consciousness.^[33]

The most commonly given answer is that we attribute consciousness to other people because we see that they resemble us in appearance and behavior: we reason that if they look like us and act like us, they must be like us in other ways, including having experiences of the sort that we do.^[34] There are, however, a variety of problems with that explanation. For one thing, it seems to violate the principle of parsimony, by postulating an invisible entity that is not necessary to explain what we observe.^[34] Some philosophers, such as Daniel Dennett in an essay titled The Unimagined Preposterousness of Zombies, argue that people who give this explanation do not really understand what they are saying.^[35] More broadly, philosophers who do not accept the possibility of zombies generally believe that consciousness is reflected in behavior (including verbal behavior), and that we attribute consciousness on the basis of behavior. A more straightforward way of saying this is that we attribute experiences to people because of what they can do, including the fact that they can tell us about their experiences.^[36]

Animal consciousness

The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because animals, lacking the ability to express human language, cannot tell us about their experiences.^[37] Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Descartes, for example, has sometimes been blamed for mistreatment of animals due to the fact that he believed only humans have a non-physical mind.^[38] Most people have a strong intuition that some animals, such as cats and dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious, and are often based on personal interactions with pets and other animals they have observed.^[37]

Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled What Is it Like to Be a Bat?. He said that an organism is conscious «if and only if there is something that it is like to be that organism — something it is like for the organism»; and he argued that no matter how much we know about an animal’s brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself.^[39] Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent.^[40] Several psychologists and ethologists have argued for the existence of animal consciousness by describing a range of behaviors that appear to show animals holding beliefs about things they cannot directly perceive — Donald Griffin’s 2001 book Animal Minds reviews a substantial portion of the evidence.^[41]

Artifact consciousness

The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the Golem, a magically animated homunculus built of clay.^[42] However, the possibility of actually constructing a conscious machine was probably first discussed by Ada Lovelace, in a set of notes written in 1842 about the Analytical Engine invented by Charles Babbage, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a humanlike way. She wrote:

It is desirable to guard against the possibility of exaggerated ideas that might arise as to the powers of the Analytical Engine. … The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its province is to assist us in making available what we are already acquainted with.^[43]

One of the most influential contributions to this question was an essay written in 1950 by pioneering computer scientist Alan Turing, titled Computing Machinery and Intelligence. Turing disavowed any interest in terminology, saying that even «Can machines think?» is too loaded with spurious connotations to be meaningful; but he proposed to replace all such questions with a specific operational test, which has become known as the Turing test.^[44] To pass the test a computer must be able to imitate a human well enough to fool interrogators. In his essay Turing discussed a variety of possible objections, and presented a counterargument to each of them. The Turing test is commonly cited in discussions of artificial intelligence as a proposed criterion for machine consciousness; it has provoked a great deal of philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious,^[45] while David Chalmers argues that a philosophical zombie could pass the test, yet fail to be conscious.^[46]

In a lively exchange over what has come to be referred to as «The Chinese room Argument», John Searle sought to refute the claim of proponents of what he calls ‘Strong Artificial Intelligence (AI)’ that a computer program can be conscious, though he does agree with advocates of «Weak AI» that computer programs can be formatted to «simulate» conscious states. His own view is that consciousness has subjective, first-person causal powers by being essentially intentional due simply to the way human brains function biologically; conscious persons can perform computations, but consciousness is not inherently computational the way computer programs are. To make a Turing machine that speaks Chinese, Searle gets in a room stocked with algorithms programmed to respond to Chinese questions, i.e., Turing machines, programmed to correctly answer in Chinese questions asked in Chinese, and he finds he’s able to process the inputs to outputs perfectly without having any understanding of Chinese, nor having any idea what the questions and answers could possibly mean. And, this is all a current computer program would do. If the experiment were done in English, since Searle knows English, he would be able to take questions and give answers without any algorithms for English questions, and he would be affectively aware of what was being said and the purposes it might serve: Searle passes the Turing test of answering the questions in both languages, but he’s only conscious of what he’s doing when he speaks English. Another way of putting the argument is to say computational computer programs can pass the Turing test for processing the syntax of a language, but that semantics cannot be reduced to syntax in the way Strong AI advocates hoped: processing semantics is conscious and intentional because we use semantics to consciously produce meaning by what we say.^[47]

In the literature concerning artificial intelligence (AI), Searle’s essay has been second only to Turing’s in the volume of debate it has generated.^[47] Searle himself was vague about what extra ingredients it would take to make a machine conscious: all he proposed was that what was needed was «causal powers» of the sort that the brain has and that computers lack. But other thinkers sympathetic to his basic argument have suggested that the necessary (though perhaps still not sufficient) extra conditions may include the ability to pass not just the verbal version of the Turing test, but the robotic version,^[48] which requires grounding the robot’s words in the robot’s sensorimotor capacity to categorize and interact with the things in the world that its words are about, Turing-indistinguishably from a real person. Turing-scale robotics is an empirical branch of research on embodied cognition and situated cognition^[49]

The transitivity principle

One argument in the field of philosophy of consciousness deals with what it is that makes a mental state «conscious» in the sense of there being something it is like to experience that state. David Rosenthal posits the «transitivity principle» as a possible answer to this question. This principle holds that what makes a state conscious is the individual being aware of being in that state. This happens, on Rosenthal’s account, through the use of a higher-order thought that is directed on the mental state in question.

Rosenthal cites several empirical paradigms in support of his theory. Blind-sight is one. This is a phenomenon that occurs in individuals with damage to the visual center of their brains. These individuals are often capable of relatively simple forms of visual awareness (like being able to spatially locate an x in a picture) but do not report anything concerning what it is like to experience these visual stimuli. Rosenthal claims that this can only be explained as a perception which the subject is not aware of experiencing.

Rosenthal also cites masked-priming, in which the individual is presented a priming stimulus which is quickly replaced by a masking stimulus. The individual does not report having experienced the state even though they clearly received the visual input. Again, Rosenthal claims that this can only be an instance of a visual stimulus of which the subject is not aware, and which there is therefore nothing it is like to experience.

Fred Dretske has objected to the transitivity principle on the basis that we often experience mental states that are consciously different without being aware of the conscious different. For instance, one might look at a picture of two forests. The pictures might be exactly the same except that there is one tree that is present in one picture but absent in the other. Dretske points out that what it is like to see the one forest is different from what it is like to see the other. And yet the individual looking at the pictures can easily fail to be aware that they differ at all.

Philosophical criticisms of the concept of consciousness

From the eighteenth to twentieth centuries many philosophers concentrated on relations, processes and thought as the most important aspects of consciousness. These aspects would later become known as «access consciousness» and this focus on relations allowed philosophers such as Marx, Nietzsche and Foucault to claim that individual consciousness was dependent on such factors as social relations, political relations and ideology.

Locke’s «forensic» notion of personal identity founded on an individual conscious subject would be criticized in the 19th century by Marx, Nietzsche and Freud following different angles. Martin Heidegger’s concept of the Dasein («Being-there») would also be an attempt to think beyond the conscious subject.

Marx considered that social relations ontologically preceded individual consciousness, and criticized the conception of a conscious subject as an ideological conception on which liberal political thought was founded. Marx in particular criticized the 1789 Declaration of the Rights of Man and of the Citizen, considering that the so-called individual natural rights were ideological fictions camouflaging social inequality in the attribution of those rights. Later, Louis Althusser would criticize the «bourgeois ideology of the subject» through the concept of interpellation («Hey, you!»).

Nietzsche, for his part, once wrote that «they give you free will only to later blame yourself», thus reversing the classical liberal conception of free will in a critical account of the genealogy of consciousness as the effect of guilt and ressentiment, which he described in On the Genealogy of Morals. Hence, Nietzsche was the first one to make the claim that the modern notion of consciousness was indebted to the modern system of penalty, which judged a man according to his «responsibility», that is by the consciousness through which acts can be attributed to an individual subject: «I did this! this is me!». Consciousness is thus related by Nietzsche to the classic philosopheme of recognition which, according to him, defines knowledge.^[50]

According to Pierre Klossowski (1969), Nietzsche considered consciousness to be a hypostatization of the body, composed of multiple forces (the «Will to Power»). According to him, the subject was only a «grammatical fiction»: we believed in the existence of an individual subject, and therefore of a specific author of each act, insofar as we speak. Therefore, the conscious subject is dependent on the existence of language, a claim which would be generalized by critical discourse analysis (see for example Judith Butler).

Michel Foucault’s analysis of the creation of the individual subject through disciplines, in Discipline and Punish (1975), would extend Nietzsche’s genealogy of consciousness and personal identity — i.e. individualism — to the change in the juridico-penal system: the emergence of penology and the disciplinization of the individual subject through the creation of a penal system which judged not the acts as it alleged to, but the personal identity of the wrong-doer. In other words, Foucault maintained that, by judging not the acts (the crime), but the person behind those acts (the criminal), the modern penal system was not only following the philosophical definition of consciousness, once again demonstrating the imbrications between ideas and social institutions («material ideology» as Althusser would call it); it was by itself creating the individual person, categorizing and dividing the masses into a category of poor but honest and law-abiding citizens and another category of «professional criminals» or recidivists.

Gilbert Ryle has argued that traditional understandings of consciousness depend on a Cartesian outlook that divides into mind and body, mind and world. He proposed that we speak not of minds, bodies, and the world, but of individuals, or persons, acting in the world. Thus, by saying ‘consciousness,’ we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.

The failure to produce a workable definition of consciousness also raises formidable philosophical questions. When Antonio Dimasio^[51] defines consciousness as «an organism’s awareness of its own self and its surroundings,» he hasn’t said anything. The words «consciousness,» «awareness,» and «perception» convey a very passive sense, bringing up images of the homunculus observer. The idea of consciousness also implies a gratuitous distinction between awareness and sensation, as if sensation or thought is something we have to be aware of.

The neurological data shows, however, that experience is a very interactive thing. Our brain massages vast libraries of experience that it draws upon to create a coherent body and a coherent world for us. As in the act of reading a text, our reading of our bodies and the world around us is a very active thing. Maturana and Varela^[52] showed that the brain is massively involved with creating worlds of experience for us with meager input from the senses.

Evolutionary biologist Richard Dawkins^[53] sums up the interactive view of experience: «In a way, what sense organs do is assist our brains to construct a useful model and it is this model that we move around in. It is a kind of virtual reality simulation of the world.»

Consciousness and language

Because humans express their conscious states using language, it is tempting to equate language abilities and consciousness. There are, however, speechless humans (infants, feral children, aphasics, severe forms of autism), to whom consciousness is attributed despite language lost or not yet acquired. Moreover, the study of brain states of non-linguistic primates, in particular the macaques, has been used extensively by scientists and philosophers in their quest for the neural correlates of the contents of consciousness.

Julian Jaynes argued to the contrary, in The Origin of Consciousness in the Breakdown of the Bicameral Mind, that for consciousness to arise in a person, language needs to have reached a fairly high level of complexity. According to Jaynes, human consciousness emerged as recently as 1300 BCE or thereabouts. Many philosophers, including W.V. Quine and neuroscientists, including Christof Koch, contest this hypothesis, as it suggests that prior to this «discovery» of consciousness, experience simply did not exist.^[54] Ned Block argued that Jaynes had confused consciousness with the concept of consciousness, the latter being what was discovered between the Iliad and the Odyssey.^[55] Daniel Dennett argues that consciousness is like money in that having the thing requires having the concept of it, so it is a revolutionary proposal and not a ridiculous error to suppose that consciousness only emerges when its concept does.

Consciousness and Brain Evolution

Other accounts of the origin of consciousness as a brain function approach it as an adaptation, a trait that must in some fashion increase biological fitness. ^[56] Sir John C. Eccles considers the problem in his paper «Evolution of consciousness.» He argues that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness. ^[57] Budiansky, by contrast, limits consciousness to humans, proposing that human consciousness may have evolved as an adaptation to anticipate and counter social strategems of other humans, predators, and prey.^[58] Alternatively, it has been argued that the recursive circuitry underwriting consciousness is much more primitive, having evolved initially in pre-mammalian species because it improves the capacity for interaction with both social and natural environments by providing an energy saving «neutral» gear in an otherwise energy expensive motor output machine.^[59] Once in place, this recursive circuitry may well have provided a basis for the subsequent development of many of the functions which consciousness facilitates in higher organisms, as outlined by Bernard J. Baars.^[60]

Cognitive neuroscience approaches

Modern investigations into and discoveries about consciousness are based on psychological statistical studies and case studies of consciousness states and the deficits caused by lesions, stroke, injury, or surgery that disrupt the normal functioning of human senses and cognition. These discoveries suggest that the mind is a complex structure derived from various localized functions that are bound together with a unitary awareness.

Several studies point to common mechanisms in different clinical conditions that lead to loss of consciousness. Persistent vegetative state (PVS) is a condition in which an individual loses the higher cerebral powers of the brain, but maintains sleep-wake cycles with full or partial autonomic functions. Studies comparing PVS with healthy, awake subjects consistently demonstrate an impaired connectivity between the deeper (brainstem and thalamic) and the upper (cortical) areas of the brain. In addition, it is agreed that the general brain activity in the cortex is lower in the PVS state. Some electroneurobiological interpretations of consciousness characterize this loss of consciousness as a loss of the ability to resolve time (similar to playing an old phonographic record at very slow or very rapid speed), along a continuum that starts with inattention, continues on sleep, and arrives to coma and death ^[61] . It is likely that different components of consciousness can be teased apart with anesthetics, sedatives and hypnotics. These drugs appear to differentially act on several brain areas to disrupt, to varying degrees, different components of consciousness. The ability to recall information, for example, may be disrupted by anesthetics acting on the hippocampal cortex. Neurons in this region are particularly sensitive to anesthetics at the time loss of recall occurs. Direct anesthetic actions on hippocampal neurons have been shown to underlie EEG effects that occur in humans and animals during loss of recall (MacIver et al 1996; see also: http://www.stanford.edu/group/maciverlab/research.html).

Loss of consciousness also occurs in other conditions, such as general (tonic-clonic) epileptic seizures, in general anaesthesia, maybe even in deep (slow-wave) sleep. At present, the best-supported hypotheses about such cases of loss of consciousness (or loss of time resolution) focus on the need for 1) a widespread cortical network, including particularly the frontal, parietal and temporal cortices, and 2) cooperation between the deep layers of the brain, especially the thalamus, and the upper layers, the cortex. Such hypotheses go under the common term «globalist theories» of consciousness, due to the claim for a widespread, global network necessary for consciousness to interact with non-mental reality in the first place.^{[How to reference and link to summary or text]}

Brain chemistry affects human consciousness. Sleeping drugs (such as Midazolam = Dormicum) can bring the brain from the awake condition (conscious) to the sleep (unconscious). Wake-up drugs such as Anexate reverse this process.
Many other drugs (such as alcohol, nicotine, Tetrahydrocannabinol (THC), heroin, cocaine, LSD, MDMA) have a consciousness-changing effect.

There is a neural link between the left and right hemispheres of the brain, known as the corpus callosum. This link is sometimes surgically severed to control severe seizures in epilepsy patients. This procedure was first performed by Roger Sperry in the 1960s. Tests of these patients have shown that, after the link is completely severed, the hemispheres are no longer able to communicate, leading to certain problems that usually arise only in test conditions. For example, while the left side of the brain can verbally describe what is going on in the right visual field, the right hemisphere is essentially mute, instead relying on its spatial abilities to interact with the world on the left visual field. Some say that it is as if two separate minds now share the same skull, but both still represent themselves as a single «I» to the outside world.^{[How to reference and link to summary or text]}

The bilateral removal of the centromedian nucleus (part of the Intra-laminar nucleus of the Thalamus) appears to abolish consciousness, causing coma, PVS, severe mutism and other features that mimic brain death. The centromedian nucleus is also one of the principal sites of action of general anaesthetics and anti-psychotic drugs. This evidence suggests that a functioning thalamus is necessary, but not sufficient, for human consciousness.

Neurophysiological studies in awake, behaving monkeys point to advanced cortical areas in prefrontal cortex and temporal lobes as carriers of neuronal correlates of consciousness. Christof Koch and Francis Crick argued that neuronal mechanisms of consciousness are intricately related to prefrontal cortex — the most advanced cortical area. Rodolfo Llinas proposes that consciousness results from recurrent thalamo-cortical resonance where the specific (dorsal thalamus) thalamocortical system (content) and the non-specific (centromedial thalamus) thalamocortical system (context) interact at gamma band frequency via time coincidence. According to this view the «I» represents a global predictive function required for intentionality.^[62][63] Experimental work of Steven Wise, Mikhail Lebedev and their colleagues supports this view. They demonstrated that activity of prefrontal cortex neurons reflects illusory perceptions of movements of visual stimuli. Nikos Logothetis and colleagues made similar observations on visually responsive neurons in the temporal lobe. These neurons reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry). The studies of blindsight — vision without awareness after lesions to parts of the visual system such as the primary visual cortex — performed by Lawrence Weiskrantz and David P. Carey provided important insights on how conscious perception arises in the brain. In recent years the theory of two visual streams, vision for perception versus vision for action was developed by Melvyn Goodale, David Milner and others. According to this theory, visual perception arises as the result of processing of visual information by the ventral stream areas (located mostly in the temporal lobe), whereas the dorsal stream areas (located mostly in the parietal lobe) process visual information unconsciously. For example, quick catching of the ball would engage mostly the dorsal stream areas, and viewing a painting would be handled by the ventral stream. Overall, these studies show that conscious versus unconscious behaviors can be linked to specific brain areas and patterns of neuronal activation.^{[How to reference and link to summary or text]}. However, neuroscience only focuses on the neural correlates of consciousness. The hard problem of consciousness is to explain how all these flows and electrochemical processes in the brain give rise to the inner experience of subjective awareness.

One of the promising approaches in modern Neuroscience is Operational Architectonicstheory of brain-mind functioning developed by Andrew and Alexander Fingelkurts. This theory states that whenever any pattern of phenomenality (including reflective thought) is instantiated, there is neuro-physiological pattern (revealed directly by EEG) of appropriate kind that corresponds to it.^[64][65] These neuron-physiological EEG patterns (expressed as the virtual operational modules) are brought to existence by joint operations of many functional and transient neuronal assemblies in the brain.^[66] The activity of neuronal assemblies per se is ‘hidden’ in the complex nonstationary structure of EEG field.^[67] Therefore, a proper EEG analysis is needed that would be able to reveal the EEG architecture which reflects or instantiates the kind of phenomenal world (considering that there should be the ‘well-defined’ and ‘well-detected’ EEG phenomena) which humans subjectively experience. Currently available EEG methods can reveal the EEG architecture which is amazingly similar to the architecture of a phenomenal world of consciousness (see review on EEG and Operational Architectonics).

Physical approaches

Even at the dawn of Newtonian science, Leibniz and many others were suggesting physical theories of consciousness. Modern physical theories of consciousness can be divided into three types: theories to explain behaviour and access consciousness, theories to explain phenomenal consciousness and theories to explain the quantum mechanical (QM) Quantum mind. Theories that seek to explain behaviour are an everyday part of neuroscience, some of these theories of access consciousness, such as Edelman’s theory, contentiously identify phenomenal consciousness with reflex events in the brain. Theories that seek to explain phenomenal consciousness directly, such as Space-time theories of consciousness and Electromagnetic theories of consciousness, have been available for almost a century, but have not yet been confirmed by experiment. Theories that attempt to explain the QM measurement problem include Pribram and Bohm’s Holonomic brain theory, Hameroff and Penrose’s Orch-OR theory and the Many-minds interpretation. Some of these QM theories offer descriptions of phenomenal consciousness, as well as QM interpretations of access consciousness. None of the quantum mechanical theories has been confirmed by experiment, and there are philosophers who argue that QM has no bearing on consciousness.

There is also a concerted effort in the field of Artificial Intelligence to create digital computer programs that can simulate consciousness.

Functions of consciousness

We generally agree that our fellow human beings are conscious, and that much simpler life forms, such as bacteria, are not. Many of us attribute consciousness to higher-order animals such as dolphins and primates; academic research is investigating the extent to which animals are conscious. This suggests the hypothesis that consciousness has co-evolved with life, which would require it to have some sort of added value, especially survival value. People have therefore looked for specific functions and benefits of consciousness. Bernard Baars (1997), for instance, states that «consciousness is a supremely functional adaptation» and suggests a variety of functions in which consciousness plays an important, if not essential, role: prioritization of alternatives, problem solving, decision making, brain processes recruiting, action control, error detection, planning, learning, adaptation, context creation, and access to information.^{[How to reference and link to summary or text]} Antonio Damasio (1999) regards consciousness as part of an organism’s survival kit, allowing planned rather than instinctual responses.^{[How to reference and link to summary or text]} He also points out that awareness of self allows a concern for one’s own survival, which increases the drive to survive, although how far consciousness is involved in behaviour is an actively debated issue. Many psychologists, such as radical behaviorists, and many philosophers, such as those that support Ryle’s approach, would maintain that behavior can be explained by non-conscious processes akin to artificial intelligence, and might consider consciousness to be epiphenomenal or only weakly related to function.

Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). This has been called the integration consensus. However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect (cf., Morsella, 2005).

Ervin Laszlo argues that self-awareness, the ability to make observations of oneself, evolved. Emile Durkheim formulated the concept of so called collective consciousness, which is essential for organization of human, social relations. The accelerating drive of human race to explorations, cognition, understanding and technological progress[1] can be explained by some features of collective consciousness (collective self — concepts) and collective intelligence

Tests of consciousness

As there is no clear definition of consciousness and no empirical measure exists to test for its presence, it has been argued that due to the nature of the problem of consciousness, empirical tests are intrinsically impossible. However, several tests have been developed which attempt to provide an operational definition of consciousness and try to determine whether computers and other non-human animals can demonstrate through their behavior, by passing these tests, that they are conscious.

In medicine, several neurological and brain imaging techniques, like EEG and fMRI, have proven useful for physical measures of brain activity associated with consciousness. This is particularly true for EEG measures during anesthesia[2] that can provide an indication of anesthetic depth, although with still limited accuracies of ~ 70 % and a high degree of patient and drug variability seen.

Turing Test

Though often thought of as a test for consciousness, the Turing test (named after computer scientist Alan Turing, who first proposed it) is actually a test to determine whether or not a computer satisfied his operational definition of «intelligent» (which is actually quite different from a test for consciousness or self-awareness). This test is commonly cited in discussion of artificial intelligence. The essence of the test is based on «the Imitation Game», in which a human experimenter attempts to converse, via computer keyboards, with two others. One of the others is a human (who, it is assumed, is conscious) while the other is a computer. Because all of the conversation is via keyboards (teletypes, in Turing’s original conception) no cues such as voice, prosody, or appearance will be available to indicate which is the human and which is the computer. If the human is unable to determine which of the conversants is human, and which is a computer, the computer is said to have «passed» the Turing test (satisfied Turing’s operational definition of «intelligent»).

The Turing test has generated a great deal of research and philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious,^[68] while David Chalmers, argues that a philosophical zombie could pass the test, yet fail to be conscious.^[69]

It has been argued that the question itself is excessively anthropomorphic. Edsger Dijkstra commented that «The question of whether a computer can think is no more interesting than the question of whether a submarine can swim», expressing the view that different words are appropriate for the workings of a machine to those of animals even if they produce similar results, just as submarines are not normally said to swim.

Philosopher John Searle developed a thought experiment, the Chinese room argument, which is intended to show problems with the Turing Test.^[70] Searle asks the reader to imagine a non-Chinese speaker in a room in which there are stored a very large number of Chinese symbols and rule books. Questions are passed to the person in the form of written Chinese symbols via a slot, and the person responds by looking up the symbols and the correct replies in the rule books. Based on the purely input-output operations, the «Chinese room» gives the appearance of understanding Chinese. However, the person in the room understands no Chinese at all. This argument has been the subject of intense philosophical debate since it was introduced in 1980, even leading to edited volumes on this topic alone.

The application of the Turing test to human consciousness has even led to an annual competition, the Loebner Prize with «Grand Prize of $100,000 and a Gold Medal for the first computer whose responses were indistinguishable from a human’s.» For a summary of research on the Turing Test, see here.

Mirror test

See also the concept of the Mirror stage by Jacques Lacan

With the mirror test, devised by Gordon Gallup in the 1970s, one is interested in whether animals are able to recognize themselves in a mirror. The classic example of the test involves placing a spot of coloring on the skin or fur near the individual’s forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves. Humans (older than 18 months), great apes (except for gorillas), bottlenose dolphins, pigeons [3], and elephants [4] have all been observed to pass this test. The test is usually carried out with an identical ‘spot’ being placed elsewhere on the head with a non-visible material as a control, to assure the subject is not responding to the touch stimuli of the spot’s presence. Proponents of the hard problem of consciousness claim that the mirror test only demonstrates that some animals possess a particular cognitive capacity for modelling their environment, but not for the presence of phenomenal consciousness per se.

Delay test

One problem researchers face is distinguishing nonconscious reflexes and instinctual responses from conscious responses. Neuroscientists Francis Crick and Christof Koch have proposed that by placing a delay between stimulus and execution of action, one may determine the extent of involvement of consciousness in an action of a biological organism.

For example, when psychologists Larry Squire and Robert Clark combined a tone of a specific pitch with a puff of air to the eye, test subjects came to blink their eyes in anticipation of the puff of air when the appropriate tone was played. When the puff of air followed a half of a second later, no such conditioning occurred. When subjects were asked about the experiment, only those who were asked to pay attention could consciously distinguish which tone preceded the puff of air.

Ability to delay the response to an action implies that the information must be stored in short-term memory, which is conjectured to be a closely associated prerequisite for consciousness. However, this test is only valid for biological organisms. While it is simple to create a computer program that passes, such success does not suggest anything beyond a clever programmer.^[54]

Scientific study

For many decades, consciousness as a research topic was avoided by the majority of mainstream scientists, because of a general feeling that a phenomenon defined in subjective terms could not properly be studied using objective experimental methods.^[71] In 1975 George Mandler published an influential psychological study which distinguished between slow, serial, and limited conscious processes and fast, parallel and extensive unconscious ones.^[72] Starting in the 1980s, an expanding community of neuroscientists and psychologists have associated themselves with a field called Consciousness Studies, giving rise to a stream of experimental work published in books,^[73] journals such as Consciousness and Cognition, and methodological work published in journals such as the Journal of Consciousness Studies, along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness.^[74]

Modern scientific investigations into consciousness are based on psychological experiments (including, for example, the investigation of priming effects using subliminal stimuli), and on case studies of alterations in consciousness produced by trauma, illness, or drugs. Broadly viewed, scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In either case, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.^[25]

Measurement

File:Necker cube.svg

Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted operational definition. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion that is used is verbal report: in other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness.^[75] For example, subjects who stare continuously at a Necker Cube usually report that they experience it «flipping» between two 3D configurations, even though the stimulus itself remains the same.^[76] The objective is to understand the relationship between the conscious awareness of stimuli (as indicated by verbal report) and the effects the stimuli have on brain activity and behavior. In several paradigms, such as the technique of response priming, the behavior of subjects is clearly influenced by stimuli for which they report no awareness.^[77]

Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.^[78] For one thing, if verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected.^[79] Daniel Dennett has argued for an approach he calls heterophenomenology, which means treating verbal reports as stories that may or may not be true, but his ideas about how to do this have not been widely adopted.^[80] Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language: this approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. As a third issue, philosophers who dispute the validity of the Turing test may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness.^[81]

Although verbal report is in practice the «gold standard» for ascribing consciousness, it is not the only possible criterion.^[78] In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent.^[82] The scientific literature regarding the neural bases of arousal and purposeful movement is very extensive. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness.^[77] Studies of the neuroscience of free will have also shown that the experiences that people report when they behave purposefully sometimes do not correspond to their actual behaviors or to the patterns of electrical activity recorded from their brains.^[83]

Another approach applies specifically to the study of self-awareness, that is, the ability to distinguish oneself from others. In the 1970s Gordon Gallup developed an operational test for self-awareness, known as the mirror test. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual’s forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves.^[84] Humans (older than 18 months) and other great apes, bottlenose dolphins, pigeons, and elephants have all been observed to pass this test.^[85]

Neural correlates

File:Neural Correlates Of Consciousness.jpg

A major part of the scientific literature on consciousness consists of studies that examine the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the neural correlates of consciousness. The hope is to find that activity in a particular part of the brain, or a particular pattern of global brain activity, will be strongly predictive of conscious awareness. Several brain imaging techniques, such as EEG and fMRI, have been used for physical measures of brain activity in these studies.^[86]

One idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) oscillations in brain activity. This idea arose from proposals in the 1980s, by Christof von der Malsburg and Wolf Singer, that gamma oscillations could solve the so-called binding problem, by linking information represented in different parts of the brain into a unified experience.^[87] Rodolfo Llinás, for example, proposed that consciousness results from recurrent thalamo-cortical resonance where the specific thalamocortical systems (content) and the non-specific (centromedial thalamus) thalamocortical systems (context) interact in the gamma band frequency via synchronous oscillations.^[88]

A number of studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness: it is possible for subjects to report a lack of awareness even when areas such as the primary visual cortex show clear electrical responses to a stimulus.^[89] Higher brain areas are seen as more promising, especially the prefrontal cortex, which is involved in a range of higher cognitive functions collectively known as executive functions. There is substantial evidence that a «top-down» flow of neural activity (i.e., activity propagating from the frontal cortex to sensory areas) is more predictive of conscious awareness than a «bottom-up» flow of activity.^[90] The prefrontal cortex is not the only candidate area, however: studies by Nikos Logothetis and his colleagues have shown, for example, that visually responsive neurons in parts of the temporal lobe reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry).^[91]

In 2011 Graziano and Kastner^[92] proposed the «attention schema» theory of awareness. In that theory specific cortical machinery, notably in the superior temporal sulcus and the temporo-parietal junction, is used to build the construct of awareness and attribute it to other people. The same cortical machinery is also used to attribute awareness to oneself. Damage to this cortical machinery can lead to deficits in consciousness such as hemispatial neglect. In the attention schema theory, the value of constructing the feature of awareness and attributing it to a person is to gain a useful predictive model of that person’s attentional processing. Attention is a style of information processing in which a brain focuses its resources on a limited set of interrelated signals. Awareness, in this theory, is a useful, simplified schema that represents attentional state. To be aware of X is to construct a model of one’s attentional focus on X.

Defining consciousness

«The evolution of the capacity to simulate seems to have culminated in subjective consciousness. Why this should have happened is, to me, the most profound mystery facing modern biology» Richard Dawkins, The Selfish Gene. Since 1976, it has remained so.

In 2004, eight neuroscientists felt it was too soon for a definition. They wrote an apology in «Human Brain Function»:^[93]

«We have no idea how consciousness emerges from the physical activity of the brain and we do not know whether consciousness can emerge from non-biological systems, such as computers … At this point the reader will expect to find a careful and precise definition of consciousness. You will be disappointed. Consciousness has not yet become a scientific term that can be defined in this way. Currently we all use the term consciousness in many different and often ambiguous ways. Precise definitions of different aspects of consciousness will emerge … but to make precise definitions at this stage is premature.»

In contrast to philosophical definitions, an operational definition can be tested experimentally, and is useful for current research. A current definition for self-awareness, proposed in the 1970s by Gordon Gallup, is known as the mirror test. An operational definition proposed in 2012 ^[94] states «consciousness is the sum of the electrical discharges occurring throughout the nervous system of a being at any given instant». What many consider consciousness may simply be the personal awareness of all the neurons delivering messages to the mind, but operational consciousness can include all neuronal activity. Extending this concept to all sentient beings, one can measure a range of consciousness based on how many and how powerfully neurons are actually firing, varying from worms to humans. One can answer the question, is someone asleep less conscious than someone thinking about a difficult problem. Although technology does not exist currently to measure this, it can be estimated by determining oxygen consumption by the brain.

To properly understand the definition of consciousness, three principal meanings have been developed and it is critical to distinguish them. Firstly, consciousness can be defined as the waking state. This essentially means that to be conscious, one needs to be awake, aroused, alert or vigilant. The stages of consciousness can range from wakefulness, to sleep to coma even. Secondly, consciousness is defined as experience, a far more subjective approach. This notion suggests that consciousness is the content of experience from one moment to another. Consciousness is highly personal, involving a conscious subject with a limited point of view. Thirdly, consciousness can be defined as the mind. Any mental state with a propositional content is considered conscious. Thus this includes beliefs, fears, hopes, intentions, expectations and desires ^[95]

Christof Koch lists the following four
definitions of consciousness in his latest book,^[96] which can be
summarized as follows:

• Consciousness is the inner mental life that we lose each night when we fall into dreamless sleep.
• Consciousness can be measured with the Glasgow Coma Scale that assesses the reactions of patients.
• An active cortico-thalamic complex is necessary for consciousness in humans, and
• Put philosophically, consciousness is what it is like to feel something.

Biological function and evolution

Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent.^[97] This has been called the integration consensus. Another example has been proposed by Gerald Edelman called dynamic core hypothesis which puts emphasis on reentrant connections that reciprocally link areas of the brain in a massively parallel manner.^[98] These theories of integrative function present solutions to two classic problems associated with consciousness: differentiation and unity. They show how our conscious experience can discriminate between infinitely different possible scenes and details (differentiation) because it integrates those details from our sensory systems, while the integrative nature of consciousness in this view easily explains how our experience can seem unified as one whole despite all of these individual parts. However, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect.^[99] Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see ^[99]

As noted earlier, even among writers who consider consciousness to be a well-defined thing, there is widespread dispute about which animals other than humans can be said to possess it.^[58] Thus, any examination of the evolution of consciousness is faced with great difficulties. Nevertheless, some writers have argued that consciousness can be viewed from the standpoint of evolutionary biology as an adaptation in the sense of a trait that increases fitness.^[100] In his paper «Evolution of consciousness,» John Eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness.^[101] Bernard Baars proposed that once in place, this «recursive» circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms.^[102] Peter Carruthers has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality.^[103] This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends.

Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes.^[104][105] No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function F being performed by conscious organism O and non-conscious organism O*, it is unclear what adaptive advantage consciousness could provide.^[106] As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an exaptation arising as a consequence of other developments such as increases in brain size or cortical rearrangement.

States of consciousness

Template:Consciousness states

File:Abbot of Watkungtaphao in Phu Soidao Waterfall.jpg

There are some states in which consciousness seems to be abolished, including sleep, coma, and death. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage.^[107] Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance.^[108]

The two most widely accepted altered states are sleep and dreaming. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions. Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed.^[109]

A variety of psychoactive drugs have notable effects on consciousness. These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, or most notably by the class of drugs known as psychedelics.^[107] LSD, mescaline, psilocybin, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. The brain mechanisms underlying these effects are not well understood, but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter serotonin play an essential role.^[110]

There has been some research into physiological changes in yogis and people who practise various techniques of meditation. Some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. It has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness.^[111]

The most extensive study of the characteristics of altered states of consciousness was made by psychologist Charles Tart in the 1960s and 1970s. Tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world); interoception (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment.^[112] Each of these, in his view, could be altered in multiple ways by drugs or other manipulations. The components that Tart identified have not, however, been validated by empirical studies. Research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual synesthesia; and changed meaning of percepts.^[113]

Phenomenology

Template:MAin

Phenomenology is a method of inquiry that attempts to examine the structure of consciousness in its own right, putting aside problems regarding the relationship of consciousness to the physical world. This approach was first proposed by the philosopher Edmund Husserl, and later elaborated by other philosophers and scientists.^[114] Husserl’s original concept gave rise to two distinct lines of inquiry, in philosophy and psychology. In philosophy, phenomenology has largely been devoted to fundamental metaphysical questions, such as the nature of intentionality («aboutness»). In psychology, phenomenology largely has meant attempting to investigate consciousness using the method of introspection, which means looking into one’s own mind and reporting what one observes. This method fell into disrepute in the early twentieth century because of grave doubts about its reliability, but has been rehabilitated to some degree, especially when used in combination with techniques for examining brain activity.^[115]

File:Neon colour spreading illusion no caption.png

Introspectively, the world of conscious experience seems to have considerable structure. Immanuel Kant asserted that the world as we perceive it is organized according to a set of fundamental «intuitions», which include object (we perceive the world as a set of distinct things); shape; quality (color, warmth, etc.); space (distance, direction, and location); and time.^[116] Some of these constructs, such as space and time, correspond to the way the world is structured by the laws of physics; for others the correspondence is not as clear. Understanding the physical basis of qualities, such as redness or pain, has been particularly challenging. David Chalmers has called this the hard problem of consciousness.^[15] Some philosophers have argued that it is intrinsically unsolvable, because qualities («qualia») are ineffable; that is, they are «raw feels», incapable of being analyzed into component processes.^[117] Most psychologists and neuroscientists reject these arguments — nevertheless it is clear that the relationship between a physical entity such as light and a perceptual quality such as color is extraordinarily complex and indirect, as demonstrated by a variety of optical illusions such as neon color spreading.^[118]

In neuroscience, a great deal of effort has gone into investigating how the perceived world of conscious awareness is constructed inside the brain. The process is generally thought to involve two primary mechanisms: (1) hierarchical processing of sensory inputs, (2) memory. Signals arising from sensory organs are transmitted to the brain and then processed in a series of stages, which extract multiple types of information from the raw input. In the visual system, for example, sensory signals from the eyes are transmitted to the thalamus and then to the primary visual cortex; inside the cerebral cortex they are sent to areas that extract features such as three-dimensional structure, shape, color, and motion.^[119] Memory comes into play in at least two ways. First, it allows sensory information to be evaluated in the context of previous experience. Second, and even more importantly, working memory allows information to be integrated over time so that it can generate a stable representation of the world—Gerald Edelman expressed this point vividly by titling one of his books about consciousness The Remembered Present.^[120]

Despite the large amount of information available, the most important aspects of perception remain mysterious. A great deal is known about low-level signal processing in sensory systems, but the ways by which sensory systems interact with each other, with «executive» systems in the frontal cortex, and with the language system are very incompletely understood. At a deeper level, there are still basic conceptual issues that remain unresolved.^[119] Many scientists have found it difficult to reconcile the fact that information is distributed across multiple brain areas with the apparent unity of consciousness: this is one aspect of the so-called binding problem.^[121] There are also some scientists who have expressed grave reservations about the idea that the brain forms representations of the outside world at all: influential members of this group include psychologist J. J. Gibson and roboticist Rodney Brooks, who both argued in favor of «intelligence without representation».^[122]

Medical aspects

The medical approach to consciousness is practically oriented. It derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. In medicine, conceptual distinctions are considered useful to the degree that they can help to guide treatments. Whereas the philosophical approach to consciousness focuses on its fundamental nature and its contents, the medical approach focuses on the amount of consciousness a person has: in medicine, consciousness is assessed as a «level» ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end.^[123]

Consciousness is of concern to patients and physicians, especially neurologists and anesthesiologists. Patients may suffer from disorders of consciousness, or may need to be anesthetized for a surgical procedure. Physicians may perform consciousness-related interventions such as instructing the patient to sleep, administering general anesthesia, or inducing medical coma.^[123] Also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as Karen Ann Quinlan,^[124] while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.^[125]

Assessment

In medicine, consciousness is examined using a set of procedures known as neuropsychological assessment.^[82] There are two commonly used methods for assessing the level of consciousness of a patient: a simple procedure that requires minimal training, and a more complex procedure that requires substantial expertise. The simple procedure begins by asking whether the patient is able to move and react to physical stimuli. If so, the next question is whether the patient can respond in a meaningful way to questions and commands. If so, the patient is asked for name, current location, and current day and time. A patient who can answer all of these questions is said to be «oriented times three» (sometimes denoted «Ox3» on a medical chart), and is usually considered fully conscious.^[126]

The more complex procedure is known as a neurological examination, and is usually carried out by a neurologist in a hospital setting. A formal neurological examination runs through a precisely delineated series of tests, beginning with tests for basic sensorimotor reflexes, and culminating with tests for sophisticated use of language. The outcome may be summarized using the Glasgow Coma Scale, which yields a number in the range 3—15, with a score of 3 indicating brain death (the lowest defined level of consciousness), and 15 indicating full consciousness. The Glasgow Coma Scale has three subscales, measuring the best motor response (ranging from «no motor response» to «obeys commands»), the best eye response (ranging from «no eye opening» to «eyes opening spontaneously») and the best verbal response (ranging from «no verbal response» to «fully oriented»). There is also a simpler pediatric version of the scale, for children too young to be able to use language.^[123]

Disorders of consciousness

Medical conditions that inhibit consciousness are considered disorders of consciousness.^[127] This category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma.^[127][128] Differential diagnosis of these disorders is an active area of biomedical research.^{[129][130][131]} Finally, brain death results in an irreversible disruption of consciousness.^[127] While other conditions may cause a moderate deterioration (e.g., dementia and delirium) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category.

Disorder	Description
Locked-in syndrome	The patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy.
Minimally conscious state	The patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior.
Persistent vegetative state	The patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior.
Chronic coma	The patient lacks awareness and sleep-wake cycles and only displays reflexive behavior.
Brain death	The patient lacks awareness, sleep-wake cycles, and brain-mediated reflexive behavior.

Anosognosia

Main article: Anosognosia

One of the most striking disorders of consciousness goes by the name anosognosia, a Greek-derived term meaning unawareness of disease. This is a condition in which patients are disabled in some way, most commonly as a result of a stroke, but either misunderstand the nature of the problem or deny that there is anything wrong with them.^[132] The most frequently occurring form is seen in people who have experienced a stroke damaging the parietal lobe in the right hemisphere of the brain, giving rise to a syndrome known as hemispatial neglect, characterized by an inability to direct action or attention toward objects located to the right with respect to their bodies. Patients with hemispatial neglect are often paralyzed on the right side of the body, but sometimes deny being unable to move. When questioned about the obvious problem, the patient may avoid giving a direct answer, or may give an explanation that doesn’t make sense. Patients with hemispatial neglect may also fail to recognize paralyzed parts of their bodies: one frequently mentioned case is of a man who repeatedly tried to throw his own paralyzed right leg out of the bed he was lying in, and when asked what he was doing, complained that somebody had put a dead leg into the bed with him. An even more striking type of anosognosia is Anton–Babinski syndrome, a rarely occurring condition in which patients become blind but claim to be able to see normally, and persist in this claim in spite of all evidence to the contrary.^[133]

Stream of consciousness

William James is usually credited with popularizing the idea that human consciousness flows like a stream, in his Principles of Psychology of 1890. According to James, the «stream of thought» is governed by five characteristics: «(1) Every thought tends to be part of a personal consciousness. (2) Within each personal consciousness thought is always changing. (3) Within each personal consciousness thought is sensibly continuous. (4) It always appears to deal with objects independent of itself. (5) It is interested in some parts of these objects to the exclusion of others».^[134] A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or «mental continuum». In the Buddhist view, though, the «mindstream» is viewed primarily as a source of noise that distracts attention from a changeless underlying reality.^[135]

In the west, the primary impact of the idea has been on literature rather than science: stream of consciousness as a narrative mode means writing in a way that attempts to portray the moment-to-moment thoughts and experiences of a character. This technique perhaps had its beginnings in the monologues of Shakespeare’s plays, and reached its fullest development in the novels of James Joyce and Virginia Woolf, although it has also been used by many other noted writers.^[136]

Here for example is a passage from Joyce’s Ulysses about the thoughts of Molly Bloom:

Yes because he never did a thing like that before as ask to get his breakfast in bed with a couple of eggs since the City Arms hotel when he used to be pretending to be laid up with a sick voice doing his highness to make himself interesting for that old faggot Mrs Riordan that he thought he had a great leg of and she never left us a farthing all for masses for herself and her soul greatest miser ever was actually afraid to lay out 4d for her methylated spirit telling me all her ailments she had too much old chat in her about politics and earthquakes and the end of the world let us have a bit of fun first God help the world if all the women were her sort down on bathingsuits and lownecks of course nobody wanted her to wear them I suppose she was pious because no man would look at her twice I hope Ill never be like her a wonder she didnt want us to cover our faces but she was a welleducated woman certainly and her gabby talk about Mr Riordan here and Mr Riordan there I suppose he was glad to get shut of her.^[137]

Spiritual approaches

Further information: Level of consciousness (esotericism)

To most philosophers, the word «consciousness» connotes the relationship between the mind and the world. To writers on spiritual or religious topics, it frequently connotes the relationship between the mind and God, or the relationship between the mind and deeper truths that are thought to be more fundamental than the physical world. Krishna consciousness, for example, is a term used to mean an intimate linkage between the mind of a worshipper and the god Krishna.^[138] The mystical psychiatrist Richard Maurice Bucke distinguished between three types of consciousness: Simple Consciousness, awareness of the body, possessed by many animals; Self Consciousness, awareness of being aware, possessed only by humans; and Cosmic Consciousness, awareness of the life and order of the universe, possessed only by humans who are enlightened.^[139] Many more examples could be given. The most thorough account of the spiritual approach may be Ken Wilber’s book The Spectrum of Consciousness, a comparison of western and eastern ways of thinking about the mind. Wilber described consciousness as a spectrum with ordinary awareness at one end, and more profound types of awareness at higher levels.^[140]

See also

Cognitive Neuroscience

Spirituality

• Antahkarana
• Consciousness (Buddhism)
• Ego
• Higher Consciousness
• Mindstream

Philosophy

• 8-Circuit Model of Consciousness
• Bodymind
• Donald Davidson’s swamp man thought experiment («Knowing One Own’s Mind», 1987)
• Dream argument
• False Consciousness (Marxism)
• Freedom of thought
• Homunculus
• Mental body
• Mind
• Mind at Large
• Mind-body problem
• Multiple Drafts theory (Daniel Dennett) cf. also Marvin Minsky
• New Mysterianism
• Personhood Theory
• Philosophy of mind
• Philosophy of perception
• Political consciousness, pertaining to marxist and post-marxist conceptions of consciousness.
• Qualia
• Stream of consciousness
• Supervenience
• Theory of mind

Physical Hypotheses about Consciousness

• Orch-OR theory
• Electromagnetic theories of consciousness
• Holonomic brain theory
• Quantum mind
• Space-time theories of consciousness
• Simulated Reality

Groups

• Association for Consciousness Exploration
• Association for the Scientific Study of Consciousness
• Mind and Life Institute
• Mind Science Foundation

Other disciplines

• Psyche (psychology)

References

Further reading

Books

• Baars, B. (1997). In the Theater of Consciousness: The Workspace of the Mind. New York, NY: Oxford University Press. 2001 reprint: ISBN 978-0-19-514703-2

• Bar-Yam, Yaneer (2003). Dynamics of Complex Systems, Chapter 3.
• Blackmore, S. (2003). Consciousness: an Introduction. Oxford: Oxford University Press. ISBN 978-0-19-515343-9
• Block, N. (2004). The Encyclopedia of Cognitive Science.
• Carter, Rita. (2002) Exploring Consciousness. UC Berkeley Press. ISBN 0-520-23737-4
• Chalmers, D. (1996). The Conscious Mind: In Search of a Fundamental Theory. New York: Oxford University Press. ISBN 978-0-19-511789-9

*Charlton, Bruce G. "Evolution and the Cognitive Neuroscience of Awareness, Consciousness and Language"

• Cleermans, A. (Ed.) (2003). The Unity of Consciousness: Binding, Integration, and Dissociation. Oxford: Oxford University Press. ISBN 978-0-19-850857-1
• Rodney M. J. Cotterill (1998). Enchanted Looms : Conscious networks in brains and computer, Cambridge University Press.
• Damasio, A. (1999). The Feeling of What Happens: Body and Emotion in the Making of Consciousness. New York: Harcourt Press. ISBN 978-0-15-601075-7
• Dennett, D. (1991). Consciousness Explained, Boston: Little & Company. ISBN 978-0-316-18066-5
• Eccles, J.C. (1994), How the Self Controls its Brain, (Springer-Verlag).
• Griffin, D.R. (1998). Unsnarling the World-Knot: Consciousness, Freedom, and the Mind-Body Problem. Los Angeles, CA: University of California Press.
• Halliday, Eugene, Reflexive Self-Consciousness, ISBN 0-872240-01-1
• Harnad, S. (2005) What is Consciousness? New York Review of Books 52(11).
• James, W. (1902) The Varieties of Religious Experience
• Immanuel Kant (1781). Critique of Pure Reason. Trans. Norman Kemp Smith with preface by Howard Caygill. Pub: Palgrave Macmillan.
• Koch, C. (2004). The Quest for Consciousness. Englewood, CO: Roberts & Company. ISBN 978-0-9747077-0-9
• John Locke (1689). An Essay Concerning Human Understanding
• Libet, B., Freeman, A. & Sutherland, K. ed. (1999). The Volitional Brain: Towards a neuroscience of free will. Exeter, UK: Short Run Press, Ltd.
• Llinas R. (2001) «I of the Vortex. From Neurons to Self» MIT Press, Cambridge
• Metzinger, T. (2003). Being No One: the Self-model Theory of Subjectivity. Cambridge, MA: MIT Press.
• Metzinger, T. (Ed.) (2000). The Neural Correlates of Consciousness. Cambridge, MA: MIT Press. ISBN 978-0-262-13370-8
• Morgan, John H. (2007. In the Beginning: The Paleolithic Origins of Religious Consciousness. Cloverdale Books, South Bend. ISBN 978-1-929569-41-0
• Pharoah, M.C. (online). Looking to systems theory for a reductive explanation of phenomenal experience and evolutionary foundations for higher order thought Retrieved Dec.14 2007.
• Scaruffi, P. (2006). The Nature Of Consciousness. Omniware.
• Searle, J. (2004). Mind: A Brief Introduction. New York: Oxford University Press.
• Sternberg, E. (2007) Are You a Machine? The Brain, the Mind and What it Means to be Human. Amherst, NY: Prometheus Books.
• Velmans, M. (2000) Understanding Consciousness. London: Routledge/Psychology Press.
• Velmans, M. and Schneider, S. (Eds.)(2006) The Blackwell Companion to Consciousness. New York: Blackwell.

Papers

• Baars, Bernard J and Stan Franklin. 2003. How conscious experience and working memory interact. Trends in Cognitive Sciences 7: 166–172.
• Chalmers, D. (1995). The puzzle of conscious experience. Scientific American, 273, 62-68.
• Chalmers, D.J. (1995). Facing up to the problem of consciousness. Journal of Consciousness Studies, 2, 200-219.
• Franklin, S, B J Baars, U Ramamurthy, and Matthew Ventura. 2005. The role of consciousness in memory. Brains, Minds and Media 1: 1–38, pdf.
• Goswami, A. (1990). Consciousness in quantum physics and the mind-body problem. The Journal of Mind and Behavior, 11, 75-96.
• Llinas R.,Ribary,U. Contreras,D. and Pedroarena, C. (1998) «The neuronal basis for consciousness» Phil. Tranns. R. Soc. London, B. 353:1841-1849
• Lowe, E.S. (1995). There are no easy problems of consciousness. Journal of Consciousness Studies, 2, 266-271.
• Morsella, E. (2005). The Function of Phenomenal States: Supramodular Interaction Theory. Psychological Review, 112, 1000-1021.
• Penrose, R., Hameroff, S. R. (1996), ‘Conscious Events as Orchestrated Space-Time Selections’, Journal of Consciousness Studies, 3 (1), pp. 36-53.
• Shanon, B. (1998). What is the function of consciousness? Journal of Consciousness Studies, 5, 295-308.

External links

Academic journals & newsletters

• Anthropology of Consciousness
• Journal of Consciousness Studies
• Consciousness and Cognition
• Psyche
• Science & Consciousness Review
• ASSC e-print archive containing articles, book chapters, theses, conference presentations by members of the ASSC.

Philosophy resources

• Publications of the Tufts Center for Cognitive Studies, including Daniel Dennett
• David Chalmers’ directory of online papers on consciousness
• Intuitions about Consciousness: Experimental Studies an article describing the folk intuitions about what is a conscious agent
• Stanford Encyclopedia of Philosophy:
  • Consciousness (General)
  • Animal Consciousness
  • Higher Order Theories of Consciousness
  • Consciousness and Intentionality
  • Representational Theory of Consciousness
  • Unity of Consciousness
• Internet Encyclopedia of Philosophy:
  • Consciousness
  • Higher-Order Theories of Consciousness

Miscellaneous sites

• History of Consciousness Graduate Program, («consciousness as forms of human expression and social action manifested in historical, cultural, and political contexts») at the University of California, Santa Cruz, headed by Dr. Angela Davis* Online lecture videos, from an undergraduate course taught by Christof Koch at Caltech on the neurobiological basis of consciousness in 2004.
• Piero Scaruffi’s annotated bibliography on the mind
• Anesthesia and Drug effects on consciousness
• Brain Atlas, Brain Maps, Neuroinformatics
• Online course in consciousness at University of Virginia
• A survey course at University of Florida
• Edinburgh thesis (.ps) on consciousness including up-to-date reviews
• Consciousness-Related Engineering Anomaly Princeton
• Thy Mystery of Consciousness TIME.com
• Helen Keller Language and Consciousness
• Theory of the Red Blood Cells

Video

• Swami Radhananda discusses subtlety and consciousness