PERCEPTION (Lat. pereeptio, from perci pere. to perceive, from per, through capere, to take). A term common both to epistemology and to psychology. The questions how, in general, we come to have knowledge of an 'ex ternal' world, and what is the validity of this knowledge when attained, are questions that lie outside of the psychological sphere. Psychologi cally regarded, perception is either a specific form of mental function or a complex of mental processes, a compound conscious content (per cept).
Perception, in its functional significance, is defined by James as "the consciousness of par ticular material things present to sense." It is single and unitary. By a confusion of contents with function, it is often described as complex; but in the adult mind the impression comes to consciousness as perception; we are not con scious of the sum of sensations and of their assimilation and integration: we perceive. Logi cally, we may split up perception into the part functions of sensation, reproduction, and inte gration. just as—from another point of view— we may split it up into discrimination, localiza tion, and integral apprehension or object-intui tion. Psychologically, such divisions do not as sist us, while they may be dangerous as suggest ing that there must be corresponding part-con tents to carry the functions. "The perception is one state of mind or nothing." The problem of the psychology of perception, in this first sense, is to test the adequacy of perception to its stimuli, to trace the variation of the perceptive reaction under varying conditions of stimulation (to see, e.g. how it is that the perception of space is predominantly visual, and that of time predominantly auditory). and to follow the de velopment of the perceptive function through the lower orders of mind up to man.
When we turn to the percept, that is, to the contents submitted to structural analysis, we find. on the other hand, an unmistakable complex ity. A functionally simple intuition 'contains' a large number of sensation components. The components must not, it is true, be considered as forming a mere stun or aggregate: we do not get a percept by juxtaposing sensations. They are, on the contrary, put together on certain pat terns. arranged in certain ways under the con ditions laid down by the physiological organism whose sensations they are. In virtue of this arrangement they are, in some cases, intrinsically modified. (see FUSION.) Moreover, they do not remain constant at the different levels of mental development. Sensations that stood in the fore front of the percept at one stage of evolution have retired into the background, or dropped out altogether, at another, while the function of perception is still unchanged. We have, then, a threefold problem before us; to analyze the perceiving consciousness, and so reduce the per cept to its lowest morphological terms: to trace the patterns or arrangements of the sense-con stituents in perception—patterns of which we are nut conscious, but a knowledge of which is necessary if our reconstruction of the percept is to be adequate; and to follow the course of development of percepts, from the simplest to the most highly evolved minds. The first two ques
tions can be answered in the light of observable fact ; the third presents greater difficulties than does the corresponding question of the develop- , went of function, must always be answered by an hypothesis, based upon grounds of more or I, less probability.
Let us take as an illustration the temporal and spatial perceptions: perceptions of locality, magnitude, form, duration, time order, succes sion. etc. Our first question, as regards function, is: How nearly adequate are these perceptions to the time and space relations of the physical world? What is the least time or least space that we can cognize? What is the least temporal or spatial difference that we can perceive? What are the limits of our apprehension of complex form, of rhythm, etc.? Secondly, we have to explain the fitness of various qualitative and intensive con tents (sights. sounds) to carry the spatial and temporal functions. Thirdly, we must trace the growth of these perceptions from childhood on ward; and must, wherever possible, push our in quiry back, behind man, to the lower animals. Thus the homing instinct of bees, a localizing function, would come under investigation. On the side of structure the problems are different. In the adult mind extension and duration (qq.v.) are given as attributes of some or all sensa tions. All that we can do, then, is to trace out the conditions under which these aspects of sen sation are turned to account for localization. form perception, perception of succession, etc. The question is one of minute and painstaking analysis. We then inquire if the spatial and temporal formations show any constant difference from (or resemblance to) other modes of percep tion, e.g. the qualitative; and we find that they represent a common type, the 'colligation' or external connection, sharply contrasted with the I fusion of qualitative contents. We then have the genetic problem: the question whether men tal process, from the very first, had a temporal ' and spatial attribute, or whether extension and duration themselves are not formations, construc tions. which have by long use been so ingrained into time texture of mind that their mode of origin is no longer discoverable to introspection. So we arrive at the antithesis of 'nativistic' and 'genetic' theories of space and time which still divides psychologists into two distinct schools. The lines of inquiry, functional and analytical, are mutually helpful. but a confusion of their standpoints and problems can lead only to con fusion of result.
BIBLIOGRAPHY. Perception is discussed at Bibliography. Perception is discussed at length in all works upon normal psychology. Consult: James, Principles of Psychology (New York. 1890) : Wmult, Physio/ogisehe Psychologie (Leipzig, 1893) ; id., Outlines of Psychology, translated (Leipzig, 1898) Kiilpe, Outlines of Psychology (Loudon, 1895) ; Titchener, Pxperi mentul Psychology (New York, 1901). See As SOMATION OF IDEAS; SENSATION; IxTELLEcT.