Within-session patterns of responding when rats run in a T-maze

Free-operant responding changes systematically within experimental sessions, usually increasing and then decreasing, even when the contingencies of reinforcement remain constant within the session. The present study extended this finding to running times in a T-maze. In Experiment 1, running times changed significantly within the session. Furthermore, the within-session pattern of running times changed with changes in the amount or rate of reinforcement. In Experiment 2, the within-session change in running times was found to be independent of the accuracy of responding. In Experiment 3, manipulating whether responding and/or reinforcement occurred early in the session did not affect the pattern of running times later in the session. The present results increase the generality of within-session changes in responding to a discrete-trials procedure. Furthermore, within-session patterns of running times usually changed in a similar manner as within-session patterns of free-operant responding when similar factors were manipulated. Thus, the same factors may be producing the changes in both situations.