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in the 1960s. They made up a batch of nonsense monosyllables, some of which obey English rules of spelling and therefore are pronounceable (“glurck,” “clerft”) and then switched the consonant groups around to make others, with the same letters, that violate the rules and are not pronounceable (“rckugl,” “ftercl”). When skilled readers saw the words in tachistoscopic flashes, they could read the legal combinations far more easily than the illegal ones, even though none of the letter groups was a known word. One possible explanation was that they pronounced the words to themselves and were better able to hold pronounceable ones in short-term memory than unpronounceable ones. But Gibson repeated the experiment at Gallaudet College with deaf students who had never heard words pronounced, and she got the same results. This could only mean that in perceiving each pseudo-word, readers distinguished all the letters and instantly recognized which groups of them obeyed the rules of legitimate patterns of spelling in English and which did not.28

—Researchers working with visual illusions found that if subjects were instructed to look long at an illusion, and in some cases to let their eyes wander back and forth over it, the force of the illusion would wane. Even though the cues in the illusion mislead the mind, attentive looking enables the mind to extract much of the reality from the cues.29

—In the late 1950s and early 1960s, Irvin Rock, a young psychologist who would become a leading figure in perception research, showed subjects a square tilted at 45 degrees and asked them what it looked like; they said a diamond. He then tilted them by 45 degrees, causing the figure to be projected as a square on their retinas. But they saw it in a room with respect to which it was tilted and could feel themselves tilted with respect to that room; these two sources of information, processed by the mind, caused them still to see the square as a diamond. This simple experiment profoundly influenced Rock’s thinking about perception and led him to conclude that until perceptual phenomena have been analyzed from a psychological viewpoint, it is premature to do so on a neurophysiological level.30

These findings, and many more from studies made in the succeeding decades, made it clear that form is the most important cue for object recognition. Early in life toddlers learn to identify objects by their shape; they quickly gain the ability to distinguish between a dog and a cat, and having learned what an apple is, they recognize green ones, yellow ones and red ones as apples. Not long ago the psychologist Barbara Landau showed three-year-olds a meaningless shape and told them it was a “dax”; then she showed them other objects with the same shape but made of different materials, sizes, and colors, but the children identified each of them as a “dax.”31

And yet to this day, say Michael Gazzaniga and Todd Heatherton, “how we are able to extract an object’s form from the image on our retina is still somewhat mysterious.”32 They cite such commonplace mysteries as our ability to recognize objects from different perspectives and in unusual orientations, and to tell where one object ends and another begins, as in the case of a horse and rider. Hypotheses about how we do it are plentiful; proven theories are nonexistent.

From the 1940s on, neurophysiologists were making discoveries about visual perception that were as significant as those of the cognitivists. As early as the 1930s, they were able to record the electrical activity of small groups of nerve cells, and by the 1940s laboratory researchers had perfected glass probes containing electrodes so fine—the hairlike tip might be a thousandth of a centimer in diameter—that they could be inserted into a single cell of the retina, geniculate body, or visual cortex of a cat or a monkey that had been given local anesthetic. With this kind of apparatus, researchers could observe the individual cell’s electrical discharges when the animal was shown a light or some other display.33

This technique produced a historic