Incentive contrast undiminished by extended testing, imipramine, or chlordiazepoxide.

In three experiments rats were given alternating 1-minute access periods to two tubes containing sucrose solutions. When the tubes contained disparate concentrations (32% versus 4%), lick-rate was higher for the 32% solution than it was when both tubes contained 32% (a positive contrast effect) and less for 4% than when both tubes contained 4% (a negative contrast effect). Similar, but generally less pronounced, contrast effects were obtained in latency to initiate drinking. These contrast effects showed no sign of diminution with repeated exposure (32 days of repeated shifts in Experiments 1 and 3); they were not greatly influenced by injections of imipramine (Experiment 2) or chlordiazepoxide (Experiment 3), nor by deprivation conditions (Experiment 3), nor by deprivation conditions (Experiment 3). The results supported an explanation of simultaneous contrast in terms of sensory-perceptual processes rather than in terms of generalization decrement or emotional responses.