Knowledge of session length is a determinant of within-session response patterns in a human operant paradigm

Two experiments were conducted during which undergraduates responded during a variable-interval (VI) 60-second operant task. The first experiment consisted of either three 60-minute sessions or three 30-minute sessions. During Experiment 1 subjects were informed as to the length of the session and the number of sessions that would be conducted. During the second experiment subjects were told that they would be participating in three 60-minute sessions but they actually participated in one 30-minute session. During Experiment 1 the rate of responding increased significantly within the sessions for 30-minute sessions but did not change significantly for 60-minute sessions. Response rate did not change during the 30-minute session in Experiment 2. The results of these experiments demonstrate that, under certain circumstances, rate of responding changes within-sessions for humans. The experiments also provide some evidence that a prospective factor influences the rate of responding within an experimental session for human subjects.