Figure 4

Mean (± SEM) median Latency 1 (first latency within each VI schedule; left panels) and Latency 2-8 (right panels) as a function of mean rate of reinforcement, for each strain in epochs 1 and 2 (top and bottom panels, respectively). The insets of the right panels are mean rescaled latencies: each individual median Latency 2-8 in each schedule was divided by the median Latency 2-8 in VI 12 s of the same rat, and then logged (base 2). Thus, a rescaled latency of 3 indicates that the median latency in that VI (excluding Latency 1) was 2³ = 8 times longer than in VI 12 s. For all strains, Latency 1 did not vary systematically with rate of reinforcement, whereas Latencies 2-8 were shorter with higher rates of reinforcement. SHR latencies were generally undistinguishable from those of the other strains, with the possible exception of the shorter SHR Latencies 2-8 when reinforcement was delivered less than once per minute.