Two pigeons were trained to peck a response key under a procedure in which 5-min periods of keylight-on alternated with 6-min periods of blackout. During keylight-on periods, food reinforcement was provided for the first peck following 20 sec (E schedule), 120 sec (M schedule), or 300 sec (L schedule) into the period. In different experimental conditions, the E, M, and L schedules were presented either alone or in combination. When E and/or M schedules were presented, food reinforcement was provided in only a portion (usually one-half) of the periods. Performance under the combination conditions was roughly predicted by summing the separate E-, M-, and L-schedule performances. Deviations from adequate prediction were, however, observed, which demonstrated interactions between the E, M, and L schedules.
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