EFFECTS OF DRUGS ON RESPONSE DURATION DIFFERENTIATION .3. ACUTE VARIATION OF REINFORCED DURATION

Rats trained to hold a lever down for at least 1.0 s but less than 1.3 s could differentiate the reinforced response duration on about 50% o f the trials. The response duration frequency distribution was a norma l distribution with a peak near the minimum reinforced response durati on. Dose-effect curves were determined for the effects of phencyclidin e (PCP) and methamphetamine. Subsequently, rats continued to be traine d for 3 days a week with responses between 1.0 and 1.3 s reinforced, b ut on days when injections were given either the maximum reinforced du ration was increased to 2.3 s, or the minimum reinforced duration was lowered to 0.5. When the maximum duration was increased to 2.3 s, the percentage of reinforced responses increased to 60% and when the minim um reinforced duration was decreased to 0.5 s, the percentage of reinf orced responses increased to 89%. Despite the increased percentage of reinforced responses when the time window was widened, the effects of PCP and methamphetamine were not changed. These data suggest that the effects of drugs on response duration differentiation are not greatly influenced by transient changes in reinforcement frequency.