Story of Psychology - Morton Hunt [290]
Perception researchers now answer that “fusion” of the dissimilar images takes place in the visual cortex, resulting in a single three-dimensional image. By tracing the axons of the two optic nerves—which are made up of a million ganglion cells—and by using modern brain scan techniques to see what brain areas are activated by vision, perception researchers have been able to identify the intricate routing and processing of the incoming neural impulses. Omitting the bewildering details, suffice it to say that the impulses are split up and separated into thirty different pathways to areas of the visual cortex for pattern recognition (how things look), place recognition (where things are), color, and other characteristics. Then these and other arriving data are coordinated through a host of other pathways of the brain’s visual system to yield a final perception of a unified visual scene.4
Another interesting question, one of the most baffling, is how the image on the retina is viewed in the brain. Nerve impulses from the retina travel to the brain’s visual cortex, but what then? No screen exists in the brain on which they can be projected, so how is the incoming flow of data seen? And if it is displayed in some way there or elsewhere in the brain, who or what sees it? The question revives the ancient (and now thoroughly discredited) supposition that there is a homunculus or little man—the “I” of the mind—who perceives what arrives at the cortex. But if the homunculus is seeing that image, with what is it doing so? Eyes of some sort? Then who or what is looking at what arrives at the homunculus’s visual center? And so on, ad infinitum.
Allied to this puzzle is the question of visual memory. Every adult has an immense repertoire of images stored in his or her brain—familiar faces, houses, trees, leaves, cloud formations, beds slept in. They have been recorded, in some fashion, after even a single quick viewing. Though we cannot call all of them clearly to mind, it is by means of them that we recognize something we see a second time. In 1973 a Canadian psychologist, Lionel Standing, a man of great patience, showed ten thousand snapshots of miscellaneous subjects to volunteers at the rate of two thousand a day for five days. Later, when he showed them some of these pictures mixed in with new ones, they correctly identified two thirds of the old ones as pictures they had already seen.5 Where had they stored all the briefly seen images and in what form? When they saw a picture the second time, how did they locate and view the image in memory to compare it with the incoming one? Not by projecting the stored one on a cerebral screen, since none exists. And however they displayed it, what inside them looked at both the stored and incoming images—ah! there’s that troublesome little man again.
(Forget the little man and the screen he’s looking at. Research done in the past two decades has come up with a more realistic but more complicated answer, based in considerable part on studies of people with specific kinds of brain damage due, usually, to strokes. One woman, for instance, when asked to describe a banana, could say that it was a fruit and grows in southern climates but could not name its color. Another patient, asked to describe an elephant, said correctly that it had long legs but incorrectly that it had a neck that could reach the