Conditional choice-unique outcomes establish expectancies that mediate choice behavior.

Conditional discriminative choice tasks can be arranged such that all correct choices yield the same reinforcer or such that each type of correct choice has its own unique reinforcer. The former is the traditional "Common Outcomes" Procedure; the latter is the "Differential Outcomes" Procedure. Use of this Differential Outcomes Procedure facilitates the rate of learning, increases the asymptotic level of performance, and enhances working-memory based performances in both animals and humans. These facts have stimulated many questions and experiments about learning and memory mechanisms and fostered potential applications.