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

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

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.

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.