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

Attention is not a mysterious concentration of psychic energy; it is simply an allotment of analyzing mechanisms to a limited region of the field. To pay attention to a figure is to make certain analyses of, or certain constructions in, the corresponding part of the icon.

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.

The attentive synthesis of any particular letter or figure takes an appreciable time, of the order of 100ms...If a whole row of letters is to be identified, they must be synthesized one at a time... To "identify" generally means to name, and hence to synthesize not only a visual object but a linguistic-auditory one... Hence the span of apprehension is limited to what can be synthesized, and then verbally stored.