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Two avoidance-conditioning experiments in which responding delayed shocks are reported. Rats receiving an average of two shocks per minute (imposed condition) could produce, by pressing a bar, a 3-min altcrnate condition. Six (Experiment I) or more (Experiment II) shocks occuirred in the alternate condition. All shocks in the alternate condition were delayed and delivered at 1-sec intervals. With long delays, all subjects produced the alternate condition and spent a large percentage of each session in the alternate condition. The first experiment demonstrated that the longer the delay from onset of the alternate condition to onset of the shocks, the more session time spent in the alternate condition. The second experiment indicated that despite increased shock frequency, behavior is acquired and maintained when responding leads to sufficient delay. Individual subjects produced the alternate condition by bar pressing in essentially one of two patterns. One pattern, termed postshock, involved bar pressing immediately after shock; the other, termed posttransition, involved responding immediately after the transition from the alternate to the imposed condition. These results indicate that shock-frequency reduction is not necessary for avoidance conditioning; delay to shock onset is sufficient.Key words: aversive control, avoidance, delayed shock, shock frequency, ratsMany avoidance-conditioning procedures involve both delay to slhock and shock-frequency reduction. In free-operant avoidance (Sidman, 1953), for example, a response interrupts a series of shocks for several seconds. A response produces both an overall reduction in the number of shocks and an increased delay to the next shock. Herrnstein and Hineline (1966) manipulated the probability of shock following a response. During random shocks to rats, a response terminated a highprobability shock schedule and introduced a low-probability shock schedule. just as in the tion with decreased delay to shock. Rats could respond and produce one shock immediately, and simultaneously prevent a series of five shocks later. By responding, the animal could reduce the overall number of shocks per trial (shock-frequency reduction) but only by receiving an immediate shock (reduced delay). This procedure was studied when an escape response was possible and when no escape was possible. Of the four subjects receiving the no-escape procedure, two subjects showed clear acquisition when a shuttle response was required, but two other animals failed to acquire when a bar-press response was required.In an investigation of the role of delay to shock, Hineline (1970) employed a discrete trial b3ar-press procedure in which a response delayed the onset of a single shock for 10 sec, without changing the overall shock frequency. When shock frequency did not change, rats responded. In a further imianipulation, Hineline (1970) fouLd(i that responding was eliminated when responding led to a 10-sec delay an(d to an increase in the shock frequency.The present investigations examined response-...

Three negative reinforcement experiments employing a key-peck response are described. In Experiment I, pigeons shocked on the average of twice per minute (imposed condition) could produce, by pecking a key, an alternate condition with correlated stimuli. Delayed shocks were added, across sessions, to the alternate condition until pecking stopped. Two of three pigeons continued to peck despite a 100% increase in shock frequency. In Experiment II, pigeons were shocked in the imposed condition four times per minute. The postresponse delay to shock was held constant by delivering, in the alternate condition, the next shock, or the next two, three, or four shocks from the imposed-condition shock schedule. All three subjects continued to peck with no change in delay to the first two postresponse shocks but with a 75% reduction in shock frequency. In Experiment III, a response produced an immediate shock followed by a shock-free period. Three of four subjects continued to respond despite reduced delay to shock. Delay-to-shock or shock-frequency reduction was sufficient to maintain key pecking, but neither was necessary. The conditions that negatively reinforce the pigeon's key peck were similar to conditions that negatively reinforce the rat's bar press.

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