Attention
Attention, broadly defined is a selective processing mechanism (or rather, group of mechanism) that enhances and selects perceptual information or executing actions and hire level cognition. Attention and action required effort, and under normal circumstances, the hire the demands of a course of action the greater the effort required to sustain or level of efficacy.
The doctrine of attention is the nerve of the whole psychological system and that as men judge of it so shall they be judge before the general tribunal of psychology the concept of Attention unpopular because it is most applicable where simple rules break down. Only the functionalists who were more interested in describing behavior than in developing theories about it, kept alive the concern with specific aspects of Attention.