Perception (from Lat. percipere, to perceive), in psychology, the term specially applied to the mental process by which the mind becomes conscious of an external object; it is the mental completion of a sensation, which would otherwise have nothing but a momentary existence coextensive with the duration of the stimulus, and is intermediate between sensation and the "ideal revival," which can reinstate a perceptual consciousness when the object is no longer present. This narrow and precise usage of the term "perception" is due to Thomas Reid, whose view has been generally adopted in principle by modern psychologists. On the other hand some psychologists decline to accept the view that the three processes are delimited by sharp lines of cleavage. It is held on the one hand that sensation is in fact impossible as a purely subjective state without cognition; on the other that sensation and perception differ only in degree, perception being the more complex. The former view admits, which the latter practically denies, the distinction in principle. Among those who adopt the second view are E. B. Titchener and William James. James (Principles of Psychology, ii. 76) compares sensation and perception as "the barer and the richer consciousness," and says that "beyond the first crude sensation all our consciousness is a matter of suggestion, and the various suggestions shade gradually into each other, being one and all products of the same psychological machinery of association." Similarly Wundt and Titchener incline to obliterate the distinction between perception and ideal revival. Prior to Reid, the word perception had a long history in the wider sense of cognition in general. Locke and Hume both use it in this sense, and regard thinking as that special kind of perception which implies deliberate attention.
(See PSYCHOLOGY.)
