Pooled DRL performance. Cumulative probability distributions of IRTs [p(IRT <x)] in 3 DRL schedules. Distributions were constructed by pooling data across rats of each strain. Insets are corresponding probability densities; strains are identified by corresponding symbols. Curves in the cumulative distributions are fits of the Temporal Regulation (TR) model (Equation 1) to the performance of each strain. The distribution of IRTs was centered near the target time (vertical dotted lines) in DRL 5 s and DRL-LH 5 s, but not in DRL 60 s. Fewer than 4% of IRTs were reinforced in DRL 60 s.