Steven Pinker -- How the Mind Works - Hampshire High Italian ...

Thinking Machines 89Our everyday ease in generalizing our knowledge is one class of evidencethat we have several kinds of data representations inside our heads. Mentalrepresentations also reveal themselves in the psychology laboratory.With clever techniques, psychologists can catch a mind in the act of flippingfrom representation to representation. A nice demonstration comesfrom the psychologist Michael Posner and colleagues. Volunteers sit infront of a video screen and see pairs of letters flashed briefly: A A, forexample. They are asked to press one button if the letters are the same,another button if they are different (say, A B). Sometimes the matchingletters are both uppercase or both lowercase (A A or a a); that is, they arephysically identical. Sometimes one is uppercase and one is lowercase (Aa or a A); they are the same letter of the alphabet, but physically different.When the letters are physically identical, people press the buttons morequickly and accurately than when they are physically different, presumablybecause the people are processing the letters as visual forms and cansimply match them by their geometry, template-style. When one letter isA and the other letter is a, people have to convert them into a format inwhich they are equivalent, namely "the letter a"; this conversion addsj about a tenth of a second to the reaction time. But if one letter is flashedI and the other follows seconds later, it doesn't matter whether they werephysically identical or not; A-then-A is as slow as A-then-a. Quick tem->4ilate-matching is no longer possible. Apparently after a few seconds themind automatically converts a visual representation into an alphabeticone, discarding the information about its geometry.Such laboratory legerdemain has revealed that the human brain usesat least fouiLmajor formats ofjgpre^ejitation. One format is the.visualimage, which is like a template in a two-dimensional, picturelike mosaic.(Visual images are discussed in Chapter 4.) Another is a phonologicalrepresentation, a stretch of syllables that we play in our minds like a tapeloop, planning out the mouth movements and imagining what the syllablessound like. This stringlike representation is an important componentof our short-term memory, as when we look up a phone number andsilently repeat it to ourselves just long enough to dial the number. Phonologicalshort-term memory lasts between one and five seconds and canhold from four to seven "chunks." (Short-term memory is measured inchunks rather than sounds because each item can be a label that points