Perceptual learning enhances retrospective revaluation of conditioned flavor preferences in rats.

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination.