Reflections on abnormal colour vision and theories of colour.

Historically, physiology is the daughter of pathology. Healthy people struggling with an overwhelming nature had no time to bother with the workings of their organs, and doctors-naturallywere always preoccupied with disease. For them the argument from malfunction to normal function has become almost second nature and the successes of this approach in such fields as neurology, endocrinology, and other special branches of physiology are indeed impressive. But in other more general ways, the argument from disease to health has been less useful. Teratology has not much contributed to studies of normal development and the psychologies based on the study of neuroses are of rather limited use. Nearer our theme the study of the deaf has only modestly contributed to the theory of hearing, and the study of the blind little to the understanding of vision. But the exploration of minor deficiencies of the sense organs, which do not entirely abolish function but only impair it, can be more rewarding and in this respect genetical disability has a special role to play. It provides the geneticist with an opportunity to repay some of the debts to the other sciences which he has incurred in the past. The purpose of this paper is broadly to survey colour vision work from Young's (1807) time to the present, and to find out to what extent the investigation of people with abnormal colour vision can contribute to our understanding of colour perception and indeed to our ideas of what colour is.