Comparative psychology of surprising nonreward.

The surprising or unexpected omission of an appetitive reinforcer has at least two effects: An allocentric effect according to which the organism updates knowledge about the environment, and an egocentric effect that allows the organism to learn about its own emotional reaction to the change. This egocentric effect (traditionally called frustration) is correlated to activation of the hypothalamic-pituitary-adrenal axis, can be modulated by treatment with anxiolytics, and is expressed in terms of behavioral changes that have an emotional component (e.g., agonistic behavior). It is hypothesized that all vertebrates share the mechanisms underlying the allocentric effect, but only mammals possess the mechanisms underlying the egocentric effect. It is further argued that frustrative mechanisms evolved in early mammals from those underlying fear conditioning.