Paying attention is not just analyzing carefully; rather, it is a constructive act... What we build has only the dimensions we have given it. - Ulric Neisser

Given such a sweeping definition, it is apparent that cognition is involved in everything a human being might possibly do; that every psychological phenomenon is a cognitive phenomenon. But although cognitive psychology is concerned with all human activity rather than some fraction of it, the concern is from a particular point of view. Other viewpoints are equally legitimate and necessary. Dynamic psychology, which begins with motives rather than with sensory input, is a case in point. Instead of asking how a man's actions and experiences result from what he saw, remembered, or believed, the dynamic psychologist asks how they follow from the subject's goals, needs, or instincts.

The fact that the span of apprehension averages only four or five... probably results from the high rate of encoding. In a tachistoscopic experiment the subject must read the fading icon as rapidly as possible.

If we allow several figures to appear at once, the number of possible input configurations is so very large that a wholly parallel mechanism, giving a different output for each of them, is inconceivable.