EFFECTS OF COCAINE ON BRIEFLY SIGNALED VERSUS COMPLETELY SIGNALED DELAYS TO REINFORCEMENT

Key pecking by 4 pigeons was maintained by a multiple schedule consist ing of two variable-interval 60-s schedules wherein each food presenta tion followed a nonresetting 27-s delay that was either briefly signal ed at its outset or completely signaled. Brief-signal duration was adj usted so that response rates maintained by the briefly and completely signaled delays of reinforcement were similar. In general, acute admin istration of small to intermediate doses (0.3 to 3.0 mg/kg) of cocaine produced either small increases in response rates in both components or no change, and larger doses (5.6 to 13.0 mg/kg) decreased response rates. Chronic (i.e., daily) cocaine administration (10.0 mg/kg) resul ted in tolerance to the rate-decreasing effects in both components. Co caine's effects were generally similar whether delays were completely or briefly signaled. Discontinuation of cocaine administration and sub sequent removal of the delay signals also had similar effects in both components of the multiple schedule. Taken together, these results are consistent with the view that the two types of delay signals were equ ally effective in maintaining responding during the variable-interval schedules.