Extinction makes conditioning time-dependent.

Two experiments explored whether forgetting of an association depended on previous extinction of a different association in rats. Experiment 1 found that when rats were conditioned and extinguished with flavor X, a subsequently acquired conditioned aversion to flavor Y was reduced by a 19-day retention interval, something that did not occur when X and the US were initially presented unpaired. Experiment 2 found that when rats received training and extinction in one of two tasks (conditioned aversion to sucrose in Experiment 2a, and running for water in a straight alley in Experiment 2b), subsequent learning of the alternative task was partially forgotten over the 19-day retention interval. These results are similar to those previously found when manipulating physical and conceptual contexts in rats and humans, respectively, and suggest that the passage of time may play a role similar to the one played by the change in physical or conceptual contexts on information retrieval.