Heart rate of rats was recorded in the Estes-Skinner conditioned emotional response situation. Response to the conditioned stimulus was a decrease in rate. The change in heart rate was conditioned more slowly than suppression of bar-pressing; it was of shorter duration and was more variable than suppression.
Thirteen groups of rats were given two types of retention tests 0, 1, 6, or 24 hr. following exposure to electric shock (preshock). When amount of time spent in situations either identical to or different from the preshock apparatus was measured, performance was determined by the stimuli paired with preshock at short retention intervals, and by the location in which the rat was placed at the beginning of testing at long retention intervals. In a one-way avoidance situation, performance was determined by the stimuli paired with preshock at both short and long retention intervals. Although the effects of preshock as assessed by the two tests seemed different at long retention intervals, both sets of results were interpreted in terms of the flattening of generalization gradients over time.
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