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.

Olfactory learning and odor memory in the rat.

Rats were trained on a series of 9 tasks, each of which required discrimination among 8 different and unique odors. Discrimination accuracy improved across successive problems and, by the end of training, most rats made few errors after their initial exposure to each new odor. Despite the number of stimuli to be discriminated, this acquisition of a learning set was not appreciably different from that demonstrated in an earlier study that used only 2 odors per task. In subsequent retention tests, most rats also showed excellent memory for odors used in prior problems.