Perceptual learning with a sodium depletion procedure.

Rats in a state of salt need prefer a flavor that has previously been paired with saline (Experiment 1). In Experiments 2 and 3, rats exposed to 2 saline concentrations, presented either concurrently or on separate trials, and each paired with a different flavor, showed a preference for the flavor that had been associated with the stronger saline. This effect was substantial, however, only in those rats that had experienced the concurrent exposure schedule. This effect cannot be attributed to a difference in the strength of within-compound associations produced by the 2 preexposure schedules (Experiment 4). It is suggested that concurrent preexposure can engage a learning process that enhances the discriminability of the preexposed stimuli.