The application of differential outcomes to a cocaine--saline discrimination procedure

This study examined the effects of differential outcomes on the speed of acquisition of a cocaine vs saline discrimination. Two groups of male Sprague-Dawley rats were trained to discriminate 8.0 mg/kg cocaine from saline. The experimental group was exposed to differential outcomes, where correct responses following the different injections (discriminative stimuli) were correlated with a particular outcome (either sweetened condensed milk or tap water). The control group received either sweetened condensed milk or tap water at random following cocaine and saline injections. Acquisition of schedule control and three progressively difficult testing criteria were examined. The differential outcomes group came under schedule control and reached the three progressively difficult testing criteria in significantly fewer sessions than the control group. To determine whether differential outcomes during training influenced the generalization to other doses of cocaine, substitution tests were administered with several other doses of cocaine (0.0-10.0 mg/kg) to both groups. Similar cocaine dose-response functions were observed with the differential outcome group and the control group and there was not a statistically significant effect of differential outcomes on the cocaine generalization curve.