Researchers in the United States have discovered that the brain uses two different systems to detect errors.
The study published in Science may shed new light on how we control our ability to play music, speak and even to walk.
Lead researcher Professor Gordon Logan from Vanderbilt University in Tennessee said we do many things on autopilot, but researchers never knew how that autopilot was controlled.
In experiments using a pool of 22 expert typists, the researchers discovered that the hands know when an error is made, even when the brain does not.
In the first experiment, a word would appear on a screen and the typists had to type it underneath. In 6% of the words typed, the researchers would alter the typists' correctly typed word for an incorrect one. Researchers also surreptitiously corrected 45% of errors made by the typists without telling them.
When the typists were asked to evaluate their performance, they took the blame for 70% of the 'false' errors, but also took the credit for about 90% of the incorrect words which had been secretly corrected by the researchers.
You can't fool the fingers
But while they might have been fooled by the visual trickery, their fingers knew better.
Researchers discovered that the typists' fingers slowed down after they had typed a mistake, even when it was corrected and they subsequently reported they had not made a mistake.
They also found their fingers did not slow down, even when researchers had inserted a false error. Even though they could see an incorrect word on screen, their fingers didn't react because the correct word had been typed.
Logan and co-author Matthew Crump say this research suggests there are two different systems at work to spot mistakes. The 'outer loop' involves the language centres of the brain. It checks errors on screen and matches it to our original intentions.
An inner loop on the other hand operates at a largely unconscious level. It detects errors via feedback from the fingers — no matter what is done on screen, it knows what the typist actually typed, and slows down the fingers accordingly.
The researchers believe a similar pair of systems may control all kinds of abilities from playing music (to detect and correct errors) to speaking.
Logan says: "An important feature of our research is to show that people can compensate for their mistakes even when they are not aware of their errors."