Effect of intersolution interval,chlordiazepoxide, and amphetamine on anticipatory contrast

Previous experiments have shown that the intake of a 0.15% saccharin solution is suppressed if saccharin access is followed by access to 32 % sucrose in brief daily pairings. The present experiments found that: (1) the degree of suppression was not altered when no time elapsed between presentation of the two solutions each day (15 sec had been the minimum in previous experiments and was used as the control in this experiment); (2) the degree of suppression was not altered by chlordiazepoxide (6, 12, or 20 mg/kg), although the drug had large appetite-stimulating effects; (3) suppression was not influenced by amphetamine (0.25 or 0.50 mg/kg); and (4) contrast could be established or eliminated, even after extended training, by manipulating the sequences of solutions presented (saccharin-saccharin or saccharin-sucrose). The results were interpreted in terms of a contrast effect based on the learned anticipation of a preferred substance. The chlordiazepoxide data suggest that this contrast is different from successive negative contrast, and the intersolution interval data suggest that the occurrence of contrast rather than a reinforcement effect is not due to a time gap between presentations of the two solutions.