Abstract
Two experiments were to investigate the effects of US intensity upon the avoidance conditioning in a shuttle-box. In Experiment I, 40 rats were run in a 2×2 factorial design combining two US intensities (100V and 260V) and two conditioning procedures (one-way and two-way responding). All rats were trained with the acquisition procedure for 12 days, 10 trials per day. The CS-US interval was 10 seconds.Number of avoidance responses, response speed, and the number of trials to reach the nine consecutive avoidance responses were major measures of learning. The results as a whole indicated: 1) Avoidance performance in the two-way responding situation was significantly inferior to that in the one-way situation; 2) By increasing the US intensity avoidance conditioning was impaired in the two-way responding situation but it was facilitated in the one-way situation; 3) Detailed analysis of avoidance latencies indicated that there were significantly fewer short-latency avoidance responses in the two-way situation than in the one-way situation. The escape response did not differ in latency in the one-way and two-way situations. Danger of generalizing the facts obtained in the two-way avoidance conditioning situation as the universal facts of avoidance conditioning was discussed.In Experiment II the effects of US intensity upon the one-way avoidance conditioning were investigated using four shock intensities including the traumatic one (150V, 300V, 500V and 700V) and 36 rats. The details of the procedure were approximately comparable to those for the one-way avoidance groups of Experiment I. Sixty acquisition trials were run in a single day separated by rest intervals of 11-12min every 10 trials. The results as a whole indicated that no interference of avoidance conditioning was observed by increasing the US intensity to the traumatic level. Facilitation of avoidance conditioning was observed only between Group 150 and three other groups of stronger US intensity due presumably to the ceiling effect. The concept of “freezing” and the danger of using this concept in a post hoc manner without taking the situational factors into consideration were discussed.
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