Following a shaping procedure, pigeons’ pecks were maintained on concurrent, independent variable-interval schedules in which pecks on either of two keys produced different durations of shock-free time. Shock-free times scheduled as a consequence of pecking the two keys were at different times, 3 min, 1 min, or 10 sec. The relative rates of pecking a key increased as the relative duration of shock-free time for that key increased. Results are consistent with the view that the effects of negative reinforcement are parallel, but opposite in sign, to positive reinforcement and that shock-free time is analogous to food duration in positive reinforcement experiments.

By responding on a changeover key, subjects could change the prevailing unsignalled VI 65-sec. schedule to a signalled, but otherwise identical, schedule. On the signalled schedule a brief tone preceded reinforcement. Regardless of the duration of the signal (5.0, 3.0, 1.0, 0.5, or 0.1 sec.), subjects strongly preferred the signalled schedule. Withdrawal of the signal produced a rapid decline in the changeover key response rate, demonstrating that production of the signalled condition maintained the responding. Results support the information hypothesis.