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

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.

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 cope with this difficulty [of limited capacity], even a mechanical recognition system must have some way to select portions of the incoming information for detailed analysis.