Type and intensity of shock in one-way avoidance learning
Dieter, Stephen E.
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The present study sought to evaluate opposing interpretations of the facilitative effect of discontinuous over continuous shock in the shuttlebox avoidance and the discriminated lever-press avoidance situations. The stimulus generalization interpretation attributes facilitation of avoidance performance by discontinuous shock to generalization of escape responses from the stimulus complex present in the shock-off periods of discontinuous shock to the stimuli present during the CS-US interval. Another interpretation maintains that discontinuous shock possesses unspecified properties which facilitate avoidance responding independent of any effect of shock intensity. The freezing-punishment interpretation attributes facilitation of avoidance responding by discontinuous shock to the adventitious punishment of freezing responses during escape trials. Presumably, with discontinuous shock, an S may receive several punishment-of-freezing trials within a single escape trial whereas only one can be received with continuous shock. The reinforcement interpretation involves the notion of effective reinforcement. According to this position, the amount of effective reinforcement of an avoidance response is related (a) positively to the amount of fear reduction occurring with CS termination and (b) negatively to the amount of fear of situational cues present following a response. In the shuttlebox avoidance and discriminated lever-press avoidance situations, the effect of (b) is assumed to more than offset the effect of (a). Since it is assumed that less fear is conditioned with discontinuous than with continuous shock, it follows that discontinuous shock would provide greater effective reinforcement and, hence, would lead to better performance. By employing a one-way avoidance training paradigm, the present study provided an experimental contrast of the above interpretations. The stimulus generalization, unspecified property, and freezing-punishment interpretations would all predict facilitation of one-way avoidance performance by discontinuous as opposed to continuous shock although the freezing-punishment interpretation would predict no continuity-of-shock effect if freezing does not occur in the one-way situation. On the other hand, the reinforcement interpretation would predict a facilitative effect of continuous relative to discontinuous shock. This would be the case since greater fear is assumed to be conditioned with continuous shock and, in the one-way situation, little or no fear is present following the response. Ninety-six rats were randomly assigned to six experimental groups. Two types of shock (continuous and discontinuous) were arranged orthogonal to three intensities of shock (nominal values of .3, .8, and 1.6 ma.). Following an initial day of handling, Ss received 65 trials in a one-way avoidance task. Each trial consisted of S being placed in a white start box. Forty sec. later the door separating the start box and the gray safe box was raised. If S did not respond (avoid) within 5 sec. of the raising of the door, shock was administered. After leaving the start box, the S was retained in the safe box for 10 sec. before being placed in the start box for the next trial. Over the 65 trials, superior avoidance responding, in terms of percentage of avoidance responses and trial of last error, was found for the groups trained with continuous shock and stronger shock intensities. However, when the measure was the number of trials before the first avoidance, continuous shock was superior to discontinuous shock only at the weakest shock intensity and strong shock was superior to weak shock only under the discontinuous shock condition. The major conclusion offered on the basis of the present findings was that the generalization, unspecified property, and freezing-punishment interpretations were incapable of accounting for the facilitative influence of continuous as opposed to discontinuous shock in the one-way situation. On the other hand, it was concluded that the reinforcement interpretation could account for the obtained results. In addition to the findings relating to the effect of continuity-of-shock in one-way avoidance performance, the present experimental so demonstrated a positive relationship between shock intensity and one-way avoidance performance.