Pigeons respond to produce periods in which rewards are independent of responding.

Pecks by pigeons on a response key produced an ON state during which intermittent rewards were freely available, i.e., independently of responding. Pecks during the ON state caused it to remain ON. If no pecks occurred, the state changed to OFF-the key color changed-and rewards were not presented. The state remained OFF until the next response. Thus, responses controlled the state in the chamber but did not cause immediate reinforcement. Four dimensions of the schedule were varied: the rates of response-independent rewards during ON; the duration of ON produced by each peck; the pattern of rewards during ON; and the presence vs absence of exteroceptive cues during ON and OFF. The results showed that rates of responding were primarily controlled by the duration of ON produced by each response. When each response caused a long period of ON, pecks occurred infrequently; when each response caused a brief period of ON, pecks were frequent.