Odor matching and odor memory in the rat.

To assess olfactory matching-to-sample learning, rats were exposed to two odors separated by a 1-s presentation of clean air. If, and only if, the odors were identical, a response produced a water reinforcer. High levels of performance were maintained over a series of 10 novel three-odor matching-to-sample problems on this conditional go/no-go discrimination procedure. In general, performance accuracy improved over problems and errorless or near errorless performance on many stimulus combinations, particularly near the end of training, indicated acquisition of a learning set. There was little decrement in performance when the interstimulus interval was increased gradually from 1 to 10 s and matching-to-sample was not disrupted when a novel odor was presented during the interstimulus interval. These results demonstrate that rats readily learn an olfactory matching-to-sample task, maintain high levels of performance even with delays of 10-s between stimuli, and can acquire a matching-to-sample learning set. The outcomes are in agreement with prior studies demonstrating exceptional learning of instrumental tasks by rats when they are provided with odor cues.