This paper briefly reviews how subjects enhance performance by favoring some stimuli over others. The author calls the mechanism by which this is achieved "expectancy", a generic term including preparatory set, behavioral hypotheses, orienting reflex, and anticipatory goal responses. Temporal and event expectancy are contrasted. Verbal prediction before presentation of the stimulus is a method commonly used to understand expectancy state. Theoretical concensus in regard to interpreting the verbal prediction effect are presented. Also discussed is whether the subject anticipates seeing a particular stimulus or executing a particular response. The primary assumption emphasized is that expectancy is a memory phenomenon. (KS)