(E) Perception (cont.)
Localization of Impressions
To treat of the localization of impressions is really to give an account of the steps by which the psychological individual comes to a knowledge of space. At the outset of such an inquiry it seems desirable first of all to make plain what lies within our purview, and what does not, lest we disturb the peace of those who, confounding philosophy and psychology, are ever eager to fight for or against the a priori character of this element of knowledge. That space is a priori in the epistemological sense it is no concern of the psychologist either to assert or to deny. Psychologically a priori or original in such sense that it has been either actually or potentially an element in all presentation from the very beginning it certainly is not. It will help to make this matter clearer if we distinguish what philosophers frequently confuse, viz,. The concrete spatial experiences, constituting
Actual localization for the individual, and the abstract conception of space, generalized from what is found to be common in such experiences. A gannets mind "possessed of" a philosopher, if such a conceit may be allowed, would certainly afford its tenant very different spatial experiences from those he might share if he took up his quarters in a mole. So, any one who has revisited in after years a place from which he had been absent since childhood knows how largely a "personal equation," as it were, enters into his spatial perceptions. Or the same truth may be brought home to him if, walking with a friend more athletic than himself, they come upon a ditch, which both know to be twelve feet wide, but which the one feels he can clear by a jump and the other feels he cannot. In the concrete "up" is much more than a different direction from "along." The hen-harrier, which cannot soar, is indifferent to a quarry a hundred feet above itto which the peregrine, built for soaring, would at one give chasebut is on the alert as soon as it descries prey of the same apparent magnitude, but upon the ground. Similarly, in the concrete, the body is the origin or datum to which all positions are referred, and such positions differ not merely quantitatively but qualitatively. Moreover, our various bodily movements and their combinations constitute a network of co-ordinates, qualitatively distinguishable but geometrically, so to put, it, both redundant and incomplete. It is a long way from these facts of perception, which the brutes share with us, to that scientific conception of space as having three dimensions and no qualitative differences which we have elaborated by the aid of thought and language, and which reason may be see to be the logical presupposition of what in the order of mental development has chronologically preceded it. That the experience of space is not psychologically original seems obviousquite apart from any successful explanation of its originfrom the mere consideration of its complexity. Thus we must have a plurality of objectA out of B, B beside C, distant from D, and so on ; and these relations of externality, juxtaposition, and size or distance imply further specialization ; for with a mere plurality of objects we have not straight-way spatial differences. Juxtaposition, e.g., is not possible when the related object form a continuum ; but, again not any continuity is extensive. Now how has this complexity come about?
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