Concurrent Schedules: Effects of Blackout during the Changeover Delay.

Four homing pigeons were exposed to concurrent variable-interval 40-s variable-interval 120-s schedules of reinforcement with changeover delays of five durations (0, 1, 2, 4, and 8 s). The changeover delays of non-zero durations were presented with and without blackout of the experimental chamber in different conditions. Blackout eliminated or strongly reduced responding during the changeover delay. It decreased the run length of responding after the changeover delay in the variable-interval 120-s component, but it had no systematic effects on the run length after the changeover delay in the variable-interval 40-s component. In both components, the run lengths after the changeover delay increased with the duration of the delay. Blackout increased deviations from response matching, computed from measures of responding after the changeover delay. The deviations increased with the duration of the changeover delay. The reults suggest that the finding of overmatching with procedures other than the changeover delay does not depend exclusively on the absence of responding in the interval that elapses between initiation of the change to an alternative and the first response eligible for reinforcement.