In 1937 was published a book by the present author entitled Visual Perception, the principal aim of which was to collect and collate systematically the main psychological experiments on that subject, their results and conclusions. A considerable part of the book was occupied by the work of the Gestalt psychologists. And although little or no exposition of the Gestalt Theorie was included, yet the outlook and the ingenious and extensive experimental material emanating from this school of psychology inevitably dominated the book, just as at that time it dominated the minds of those psychologists who were interested in the experimental approach to perceptual problems. Since then, the main trends of thought on these problems have changed their direction. The Gestalt psychologists, and especially Kohler, have turned increasingly to theoretical speculation as to the physical basis in the cerebral cortex of the perceptual processes. On the other hand, continued study by other psychologists inspired by the original work of the Gestalt school—for instance, on the ‘constancies’—seems to have produced a mass of detailed results leading to conflicting conclusions, or to no conclusions at all. The apparently clear outlines originally drawn by the Gestalt psychologists have become blurred and dimmed. And it has seemed perhaps that their experimental results and their theories did not after all indicate a fundamental basis for the understanding of the nature of perception, but rather a one-sided exaggeration of certain features by no means the most important in perceiving as we ordinarily experience it.

Thus it seemed that the time had come for a re-assessment of the material of the author's earlier book (now out of print) in the light of more recent thought and of the mass of new experimental data. Not that the older material must all be discarded—much of it is still relevant and valuable. This is included in the present book and compared with data from more recent experiments. Some of the work of early psychologists and physiologists has, however, been omitted, since it has been dealt with admirably elsewhere by Boring (1942).

But in addition the author has within the last few years reached the conclusion that it is desirable to state, at least in very general terms, certain propositions as to the fundamental nature of the perceptual processes.