This chapter will describe some areas of perceptual research in which it has been suggested that psychological hypotheses can be replaced by known neural mechanisms. There are good reasons why a significant number of researchers in perception have always been in favour of this shift. In the first place, it is manifestly true that neural mechanisms underlie all behaviour. In an important sense they wrote these words and are now reading them. And there are those who believe that psychological knowledge is more secure when it can be linked to known physical structures. For example, the acuity of the eye falls off dramatically as one moves away from the central (foveal) region. The function linking falling acuity with degree of eccentricity is known sufficiently precisely to allow the prediction of visual performance in the periphery. But the reason why this falling-off takes place is now known: it is because of the increased ratio of rod to cone cells in the peripheral retina. The high degree of connectedness of the rod system results in high sensitivity through summation of outputs, but the price for this is the lowered resolution of the system. For many this is satisfying knowledge. A final reason for preferring neurophysiological explanations is simply that some researchers find it easier and more satisfying to think in terms of neural mechanisms, rather than in more abstract psychological terms.
The fact that perception, memory, and thought are all mediated by the central nervous system does not, however, force us to accept reductionism. The neural structures underlying mental events may be interacting in ways of which we cannot conceive and which could never be described using only the language of neurophysiology. This is said simply to warn the reader against too ready an acceptance of some of the claims to be outlined later in this chapter.
The approaches to be described have one thing in common: they invoke neural mechanisms in explanations of perceptual phenomena. We have of course met such an approach in the earlier chapter on the Gestalt theory. But this modern work differs from the Gestalt approach in two important ways. First, Köhler's physiology was highly speculative and, as it happens, largely incorrect; modern discoveries and theories are much more securely based. Second, the Gestalt psychologists, as phenomenologists, wanted to explain