Dynamics of temporal control in rats: the effects of a brief transition in interval duration

Five rats lever-pressed for liquid reinforcers delivered according to a fixed-interval (FI) reinforcement schedule, where the interval requirement changed at an unpredictable point within a session. In a short square wave (SSW) condition, eight 30-s intervals were intercalated in a series of 120-s intervals so that the intervals changed from 120 to 30 s then back to 120 s. In a long square wave (LSW) condition the intervals changed from 120 to 480 s then back to 120 s. We observed rapid temporal control of post-reinforcement wait time duration by the IFI duration in the SSW condition only: Wait times decreased significantly during a transition to shorter (30 s) intervals; whereas wait times did not reliably increase during a transition to longer (480 s) intervals. Furthermore, in the SSW condition, wait time in post-transition intervals was shorter than that observed during pre-transition intervals. The results show that rats' wait times are sensitive to moment-to-moment changes in interval duration and that the dynamics depend on the direction in which the intervals change.