Journal of the experimental analysis of behavior
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Two-key concurrent responding was maintained for three pigeons by a single variable-interval 1-minute schedule of reinforcement in conjunction with a random number generator that assigned feeder operations between keys with equal probability. The duration of blackouts was varied between keys when each response initiated a blackout, and grain arranged by the variable-interval schedule was automatically presented after a blackout (Exp. I). ⋯ In a third experiment, blackouts scheduled on a variable-interval were of equal duration on the two keys. For one key, grain automatically followed each blackout; for the other key, grain was dependent upon a response and never followed a blackout. The relative frequency of responding on the former key, i.e., the delay key, better approximated the negative exponential function obtained by Chung (1965) than the matching function predicted by Chung and Herrnstein (1967).
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Four rhesus monkeys were trained on a non-discriminated shock-avoidance schedule (baseline). Stimuli followed by response-independent shock were then presented with the avoidance baseline no longer in effect. ⋯ When the stimulus duration was short or the delay of shock was long, so that avoidance rate during the stimulus could assume any value without resulting in baseline (avoidable) shocks during the stimulus, a lowered or "suppressed" rate of responding developed during the stimulus. When the stimulus duration was long or the delay of shock was brief, so that avoidable shocks resulted from a response decrement during the stimulus, high or "facilitated" rates of responding developed for a large proportion of the time that the stimulus was present.
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A free-operant avoidance schedule was used to establish and maintain foot-treadle responding by two Homing, one White King, and two Carneaux pigeons. In the absence of responding, the interval between shocks equaled 10 sec. ⋯ The treadle response becomes highly stereotyped and interresponse time distributions obtained from terminal behavior appear very similar to data obtained from rats. It is concluded that the difficulty in training pigeons to avoid electric shock is not in establishing avoidance behavior but in attempting to evaluate such behavior with the key-peck response.
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Two hooded rats were trained to bar-press to avoid electric shock on a continuous avoidance schedule with response-shock and shock-shock intervals equal. The rate of delivery of response-independent shocks superimposed on this schedule was varied. ⋯ There was an increasing, negatively accelerated function between percentage avoidance and response rate, but there was no consistent relation between the number of shocks avoided and response rate. Response rate decreased as the potential shock rate increased, but responding was maintained even when as few as 15% of the shocks could be avoided.
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In the first of two experiments, three cotton rats (Sigmodon hispidus) and three albino rats were exposed to instrumental escape, unsignaled avoidance, and signaled avoidance, in that order. All subjects learned the escape procedure quickly, with the albino rats having generally shorter latencies, higher response rates, and requiring fewer sessions to reach the criterion. ⋯ In the second experiment, five cotton rats and four albino rats were exposed to a free-operant (Sidman) avoidance procedure with a shock-shock interval of 3 sec and a response-shock interval of 20 sec. The cotton rats initiated responding at lower shock intensities than the albino rats, but their asymptotic avoidance responding was far less effective.