Variation in sensory and perceptual processes
An organism's capacity to behave adaptively is dependent upon the information collected by its receptors. The superb raptorial equipment of a hawk would be useless in capturing prey if it were not coupled with extraordinary visual acuity. A catfish has degenerate eyes, but taste buds on his body surface enable him to scavenge successfully on the river bottom. Many of the psychological differences between species are understandable in terms of the structure of their sense organs.
Within-species heritable anomalies of sense organs are extremely common in man and his domesticated animals ( Roberts, 1940; Gates, 1946; Sorsby, 1953; Grüneberg, 1947). Many of these involve gross deformity or even the absence of a particular organ. In severe conditions such as amaurotic idiocy, there are concurrent anomalies of the central nervous system which directly impair intelligence.
We shall deal only briefly with sensory variations which result from major structural defects. Blindness and deafness have important psychological consequences, but in educational or psychotherapeutic work the genetic or non-genetic etiology of the condition is usually not important. The question of hereditary origin is more important to the genetic counselor who may have to advise on the probability of the trait appearing in siblings or offspring of the afflicted individual. Major emphasis here will be placed upon variations which are known only by their behavioral manifestations or which are most conveniently studied by psychological and psychophysical techniques.
Variations in sensory processes are deduced from behavior which may be a conditioned reflex, a change in rate of bar pressing, or a verbal report. Genetic studies in which the chief interest is the nature of the response itself are described in later chapters. Here we shall deal with researches in which emphasis is placed upon variations in