Two ways of spotting mistakes while typing

By Ed Yong | October 28, 2010 2:00 pm


I’m typing about typing. As my fingers flit over the keyboard, my brain is hard at work. It is accessing my knowledge of language, processing the information taken in through my eyes and fingers, and coordinating the movements of my fingers. And all the while, I’m looking for errors. Spotting mistakes is a crucial part of typing (and indeed, life) and according to Gordon Logan and Matthew Crump, it’s a more complicated business than it might first appear.

Using some clever digital trickery, the duo from Vanderbilt University found that the brain has two different ways of detecting typos. One is based on the characters that appear on the screen, and the other depends on the strokes of our fingers, as they tap away at the keys.

Logan and Crump asked 22 good typists to type 600 words presented on a screen, one at a time. Their efforts appeared below the target word, but all was not as it seemed. Throughout the experiment, Logan and Crump occasionally took control to the display. Sometimes, they put up the correct word, regardless of what the recruits actually typed so that their mistakes never appeared. On other trials, they deliberately introduced mistakes, which the typists hadn’t actually made.

When the volunteers made a genuine error, they slowed down afterwards. This drop in speed also happened when they made a mistake that was surreptitiously corrected, but not when a false mistake was inserted. So regardless of what the typists saw, the feedback from their fingers told them that they had slipped up and they acted accordingly. It looked as if the typists had resisted the illusion… but not quite.

After their test, Logan and Crump asked the recruits whether they noticed any shenanigans, first subtly (“Did you notice anything about the kind of errors you made?”) and then more directly (“Did you notice that on some proportion of the trials the computer may have correctly typed a word even though you made an error?”) .

The answers revealed that a substantial proportion of the volunteers had consciously fallen for the illusion and hadn’t noticed what had happened (even though their typing speed had changed accordingly). The vast majority took credit for the corrected errors and accepted the inserted ones as their own. Even when directly asked, around 20% didn’t spot anything unusual going on.

According to Logan and Crump, this “illusion of authorship” reflects the fact that typing involves two different groups of skills that spot mistakes in different ways. The “outer loop” involves the language centres of the brain and is involved in producing the words that we type. It detects errors by checking what appears on the screen and matching it to our original intentions. If what turns up looks right, the outer loop thinks all is well and if what appears is wrong, the outer loop raises the alarm. The outer loop falls for the illusion.

Meanwhile, the “inner loop” sets up the right sequence of hand movements that type out the words put forward by the outer loop. It detects errors by checking the feedback from the fingers and no matter what Logan and Crump do on the screen, it knows what the typist actually typed. The inner loop sees through the illusion but it operates at a largely unconscious level. It’s the one that slows down the typists’ fingers when they sense that the wrong keys were pressed.

The experiment suggests that the two loops do indeed have different ways of spotting errors. Logan and Crump confirmed that by putting 24 typists through a variant of their first experiment (image below, left). This time, they were asked to say whether they had typed each of the 600 words correctly, immediately after each trial. Once again, they still consciously fell for the illusion, taking the blame for around 70% of the inserted errors, and taking credit around 90% of the corrected errors. But as before, they slowed down when they had made a genuine mistake, even for trials where they had been apparently fooled.

A third experiment was even more blatant (image below, right). This time, Logan and Crump actually told their recruits about what they would do behind the scenes; their job was to tell the difference between what was right and wrong, real and fake. This time, they spotted the inserted errors well enough but amazingly, some of them still fell for the corrected ones. They were just as likely to notice the artificial correction as they were to miss it and take credit for the results.


These three experiments clearly show that two different processes prevent us from making mistakes as we type. The two loops depend on different types of feedback and they work independently; after all, it’s possible to fool one but not the other.

Logan and Crump think that a similar pair of systems may control all sorts of abilities, including playing music and speaking. An inner loop deals with all the details, such as hitting the right notes or making the right sounds. Meanwhile, an outer loop matches the result to our intentions, checking to see if we have performed the right song or communicated the right message.

Reference: Science
If the citation link isn’t working, read why here

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CATEGORIZED UNDER: Neuroscience and psychology
MORE ABOUT: errors, mistakes, typing

Comments (10)

  1. This makes sense to me. I both touch type and played the piano as a kid. I’m familiar with that finger sense–but I think there’s a third factor in music at least. There is hearing a wrong note, the fingers misfiring and hitting the wrong key, but there is also the memory of how the notes go. My fingers always seemed to know more than my memory.

  2. Just goes to show– we know more than we think we know.

  3. Leslie

    Not taking into account the numerous people who have “disabilities” when it comes to dropping words, letters, or reversing them (etc) or just don’t type well … more over, most word processors highlight typos … not sure what you really learned…

  4. This is fascinating. I’ve been a touch typist for 40+ years (learned in 6th grade) & even made my living as a digital typesetter (paid for how fast & accurate) so I imagine I’m more adept than many.

    I really wish somebody would do a research study on older dyslexics (say grade 8 to adulthood) — many report that their written output is faster, richer & more accurate when keyboarding than when handwriting. The sorts of errors that happen in handwriting (sweat clam instead of sweet calm) just don’t happen with keyboarding.

  5. Christina


    That’s really interesting that they would make fewer errors in typing than handwriting! It’s rather the opposite of how it is for non-dyslexics. I wonder if it has something to do with the greater mechanical complexity of hand-writing versus typing? That is, to produce a letter in typing you need merely hit the right button, whereas in hand-writing, one must produce a very specific set of movements.

  6. Christina @5 The “cognitive load” — so to speak — for handwriting is that the writer has to recall (a) the whole sequence of letters in the word, then (b) accurately recall the first letter in the word then (c) how to move the hand make the first letter — then (d) accurately recall the next letter in the word, then (e) shift, automatically to the next letter and then (f) how to move the hand make the letter… and so on.

    “It’s rather the opposite of how it is for non-dyslexics. ”

    I’m not sure that is true.

    Here is a rough first pass at an experimental design. (I don’t know how to describe it properly.) You recruit a relatively large sample of, say, high school seniors, matched for all the usual SES etc. PLUS matched for keyboarding proficiency. features. One group has a previous diagnosis of dyslexia & the other does not. One half of each of the experimental cohorts are given a SAT-type writing prompt that they have to complete by handwriting only; the other half is given a similar prompt that they can respond to using a keyboard. Then evaluate and compare the outcomes. Do the keyboarding dyslexic group out-perform the handwritten dyslexic group? How about the rest?

    To the best of my knowledge, this sort of study has never been done.

  7. Shade

    My experience is that I type a lot (part of my job) i seldom typo, but thats not the interesting thing.
    Whne I typo I have a decne rate of noticing, the thing is though that if i don’t notice that initial typo, I keep typing as per normal, but every letter is shifted by one.
    I type out this sentance, but I miss the letter “O” and keep typing as per normal with out noticing.

    I type this sentance as per nienak, vyr U NUAA rgw kwrrwe :I: abs jwwo rtoubf as oer nirmal.

    A little exagerated, but thats pretty much what it looks like when I miss a letter.

  8. Christina

    Liz: I was mostly referring to that type of error. While an error like “teh” or “clam” for “calm” isn’t too uncommon in typing, for a non-dyslexic it would be pretty rare in handwriting. I would suspect that there’d be fewer overall spelling errors, though, in handwriting vs typing for non-dyslexics. Overall speed is likely faster, though, for anyone with experience in typing, dyslexic or not.

  9. @Liz Ditz, Christina; tapping fingers on keyboard at the same learning time of pencil clamping and alphabet might be comfortable as speaking in mother tongue.

  10. AJ

    This may offer some clues to intuition. For example, knowing when someone is lying to us. The inner loop processes what the brain knows instinctively about a message – tone of voice, posture, eye contact, etc, which gives an impression as to the veracity of a statement. The outer loop processes the actual words being said. Despite conflicting input, we somehow know there is a lie.

    Reconciling the two may be something else all together though – which do we decide to believe? Perhaps this adds creedence to the idea of “trusting your gut” – your gut may actually be your inner loop thinking process, providing a less filtered means of knowing.


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