To cope with this difficulty [of limited capacity], even a mechanical recognition system must have some way to select portions of the incoming inform… - 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.

To deal with the whole visual input at once, and make discriminations based on any combination of features in the field, would require too large a brain, or too much "previous experience" to be plausible.