Thinking one word but writing another

A term I know from psycholinguistics is «phonologically based lexical selection error«.
That means, when looking up the words you need in your mental lexicon, you already have the almost appropriate phonetic form in mind, but then accidently choose a word instead that is phonetically very similar (i.e. differing in one sound, as in your example), but semantically misplaced.
Other examples would be He has a new commuter (instead of computer) or The noun comes after the proposition (instead of preposition).

A lexical selection error in general is when you erroneously pick a wrong word, which is, however, a valid word in your language.
Other sub-types of such lexical selection errors beyond phonologically based ones are semantically based lexical selection errors (one prominent error is choosing the exact antonym of what you mean, e.g. It’s very cold — err, hot) or errors involving morpohological stranding (e.g. They are Turking talkish).
Interestingly, many lexical selection errors still come along with correct grammaticality, as in the example I just mentioned: Although the lexical items themselves are misplaced, the inflection (i.e. -ing and -ish) is syntactically still at the right place — which is an indicator for mental lexical retrievement being a different process than building up the grammatical structure.

Such lexical selection errors are different from pure phonological errors, in that they involve words that are still part of the lexicon (just semantically misplaced), where you already pick the wrong word for your sentence before starting to pronounce it. Pure phonological errors would mostly be something like he gave the goy a book (instead of the boy) or lunder and thightening (instead of thunder and lightening), were you realise certain phonemes the wrong way but without that resulting in a phonetically similar, but semantically different word which is not a valid word of the language.
So the place where this goes wrong is a different one; it is not during the process of retrieving the words from your mental lexicon, but rather during the pronouncitation process, after you have already chosen your words and built up the grammatical structure.

So to summarise, I guess what you mean is a speech error named phonologically based lexical selection error, where you don’t just mispronounce things but rather make an error in getting the right words from your lexicon, by choosing a phonetically similar one that you then pronounce, often even inflect correctly, but that is just semantically not any meaningful in the context you want to use it.

Edit:
A comment on amls answer (I would have commented, but don’t have enough reputation):
I agree with you that there goes something wrong during monitoring which might be called «momentary aphasia», however I think this is not adressing the problem exactly: What OP wanted to know is type of speech error this is, i.e. what goes wrong in the first place to even produce such a sentence — not primarily why this might in some situations not be monitored and repaired.

A coworker appears out of the blue and asks me a question. Her eyes and tone of voice say she wants an answer now. Her request is easy, but my mind is momentarily paralyzed. I start sentences then stop them. I hesitate. I say words that are close to what I mean but not exactly. I backtrack. My coworker, an extrovert who always seems to express herself effortlessly, looks at me like, Come on, spit it out! Internally, I sigh. If only my brain would cooperate...

Has something like this ever happened to you? If so, you’re not alone. Being unable to articulate your thoughts, especially under pressure, is a common problem that many introverts regularly experience. There’s a good reason for it — and it may not be what you think. Here’s the science.

Introverts Process Information Deeply

Trying to think of exactly the right word is called “word retrieval.” And this can be hard for introverts. In social situations, this may translate to us falling behind fast-talking extroverts. At work, we may come off sounding like we don’t know what we’re talking about, even when we do. In the classroom, we may shrink from raising our hand, because we know it will be challenging for us to put our thoughts into words if we’re called on.

One reason word retrieval can be difficult for introverts is we process information deeply. We chew on ideas, turning them over and over in our minds, analyzing them from every angle. When you’re turned inward reflecting on something — even something as simple as, What should I have for dinner? — it’s hard to talk. Introverts don’t think out loud like extroverts do. We generally do our processing inwardly. Quietly. Without words.

Introverts May Favor Long-Term Memory

Another reason may have to do with long-term memory, according to Dr. Marti Olsen Laney in her book, The Introvert Advantage. Information stored in long-term memory is mostly outside of our conscious awareness. Like the name sounds, long-term memory contains information that is retained for long periods of time; in theory, it’s saved indefinitely. Some of this information is fairly easy to access, while other memories are more difficult to recall. For example, do you remember what your first day of kindergarten was like?

Contrast this with working memory (sometimes referred to as short-term or active memory), which is limited and retains information for mere seconds. Working memory is easy to access, but you don’t retain the information stored there for long, unless you move it to long-term memory.

Interestingly, Laney writes, introverts tend to favor long-term memory over working memory. Extroverts do the opposite, essentially putting information “on the tip of their tongue.”

It can be harder to reach into long-term memory to access the information stored there. The right association, or key, is needed to “pull up” the information you’re trying to recall — something that reminds you of it.

For example, if you tried to recall your first day of kindergarten, perhaps you looked around the room and noticed a pair of sneakers. This made you remember the sneakers you wore as a kid, which in turn reminded you that someone spilled milk on your shoes on the first day of kindergarten. BAM, suddenly you’re remembering more about that long-ago day.

Reaching into long-term memory can be a lengthy, complex process. This can slow down introverts when we’re speaking.

Anxiety Can Exacerbate It

And, if you happen to be even the slightest bit anxious when you’re trying to speak — like how I felt when my intimidating coworker approached me — it may be even more difficult to locate and articulate the right words. Not all introverts experience social anxiety or are shy, but it’s common for us “quiet ones” to experience at least some level of anxiety in social situations. After all, when you process information deeply — and are drained by “peopling” — it’s easy for anxiety to creep in.

Anxiety is mentally draining and can interfere with memory. The stress hormone cortisol is released in large amounts during times of anxiety. Cortisol affects the brain, and can lead to memory loss and problems with recall.

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Why Writing Is Easier

Introverts “often feel as if they express themselves better in writing than in conversation,” writes Susan Cain in her revolutionary book, Quiet. And indeed, many introverts are writers, whether professionally or casually. John Green, author of the bestselling YA novel The Fault in Our Stars, explains, “Writing is something you do alone. It’s a profession for introverts who want to tell you a story but don’t want to make eye contact while doing it.”

But it’s not just penning novels — introverts generally prefer text messages and emails to phone calls and in-person meetings. Likewise, many introverts say journaling helps them understand their thoughts and feelings better; other introverts are prolific bloggers.

Why do introverts prefer to write their thoughts rather than speak them? Again, this preference has to do with how our brains are wired: Written words use different pathways in the brain, which seem to flow more fluently for introverts, writes Laney.

What to Do When Your Mind Goes Blank

Memory is complex; it uses many different areas of the brain. Your brain stores memories in several locations and creates links between them. To yank something out of long-term memory, you need to locate the right association. The good news is most pieces of information in long-term memory were stored with several associations or “keys” for unlocking them. “If we find just one key, we can retrieve the whole memory,” writes Laney.

When you struggle to remember a word, a piece of information, or even what you did over the weekend (because that question always comes up in small talk!), try these things:

• Be still and relax.
• Give yourself permission to be quiet for a few moments. Don’t let the other person rush you.
• Buy yourself time by saying something like, “Let me think about that,” or “Hmm, let me see…” Or, give a nonverbal signal that you’re thinking, like looking away and furrowing your brow slightly.
• Let your mind wander and go where it wants. One thought may lead to another, and one of those thoughts may hold the key to unlocking the words you need from your long-term memory.

If all else fails, and words escape you, don’t feel embarrassed — your brain is doing what comes naturally to it, and that is to pause and reflect. If you’re being quiet, you’re in good company with other deep-thinking introverts; as the brilliant physicist Stephen Hawking once noted, “Quiet people have the loudest minds.”

Try breezing over any awkwardness by using humor to make light of your tongue-tied state. Or say you’re a little distracted right now, but you’ll get back to them later — by sending an email or a text.

You might like:

• 13 Relatable Struggles of a Socially Anxious Introvert
• Introverts’ and Extroverts’ Brains Really Are Different, According to Science
• Here’s What Makes Each Introverted Myers-Briggs Personality Type Angry

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