Differential Reinforcement of Response Duration (DRRD) in weanling rats: A comparison with adult subjects

Weanling (21-day) and adult (3-month-old) albino rats were reinforced for lever press durations of 0.5, 1.0, 1.5, 2.0 and 2.5 seconds. Six sessions were performed at DRRD 0.5 seconds, 12 at the other values, at a pace of 3 (at DRRD 0.5 seconds) or 6 sessions a day. Adult rats emit lower response rates, higher median response durations and earn more reinforcements than weanling subjects. The effect of age on the coefficient of variation of the response duration distribution is not significant, but this measure is, on average, higher for the weanling rats. Age-related differences are discussed in relationship to general activity, food motivation, schedule control and timing mechanisms. Methodological variables and the relationship of these results to the laws of temporal differentiation are also evaluated.