International Journal of Comparative Psychology

Red opossums ( Lutreolina crassicaudata ) were trained in a Y-maze to locate a piece of food (the initial response, Ri) and afterwards to run back to the start box (the final response, Rf) where no reward was available immediately although a new trial was scheduled after a 30-s intertrial interval. Omission of food in some of the training sessions (Sessions 2, 10, 20, and 30) led to a decrement in latencies of the Rf, but only in Sessions 10 and 20, which was interpreted as evidence that primary frustration elicited by omission of an expected reward increases the vigor of ongoing instrumental behavior. The absence of this effect in the first and last extinction sessions ruled out an account based on post-ingestion factors, such as transitory satiation. The results are discussed in relation to vertebrate research on learning phenomena thought to depend on the frustrative consequences of nonreward.