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An investigation of the Voeks postremity hypothesis Koppenaal, Richard John


This experiment was undertaken to investigate the validity of the postremity principle. This principle predicts, for recurring situations, such as maze, that a response to a given situation will be the same response that was last made to the stimuli present in that situation. The principle is hypothesized as ever-operating. The lack of perfect practical predictions in the maze situation is explained by the instability of stimuli, especially proprioceptive stimuli, from trial to trial at the same choice point. While the importance of proprioceptive stability upon successful predictions has been freely hypothesized, very little has been done to test this. One specific purpose of the present experiment was to test postremity in this regard. The other specific purpose of this experiment was to determine in what way, if any, successful predictions are related to 'right’ responses. It was noted by one investigator that the number of successful predictions increased with the number of trials (and increase in 'right’ responses). The possibility of some relationship has been hinted at by several investigators but never apparently thoroughly explored. A mental maze was used in this experiment. There were twelve choice points, each one with one 'right' and one 'wrong' choice possible. The methods used to control stability of proprioceptive stimuli consisted largely of control of motor responses and posture. In one group relatively little control of motor responses or posture was exercised, while in another group the motor responses and the posture of the subject were held constant. In a third group the stimuli were varied on certain trials. A fourth group had, in addition to stimulus constancy, any choice point that elicited a 'wrong' response repeated immediately, so that the subject corrected his response. This was done to gain more accurate recording of responses, which was hypothesized as being very difficult when the last response is 'wrong'. The analysis of the results indicated differences in the number of successful predictions only between the fourth group (repeated choice points), on the one hand, and each of the other three groups, on the other hand. Thus, no differences were found between the three groups where only stability of proprioceptive stimuli varied. Further analysis indicated postremity was a successful predictor only when it predicted a 'right' response. In relation to this finding, a simple prediction of the ‘right’ response at each choice point proved as efficient as postremity. The results led to the conclusion that the obtained differences in the number of successful predictions between Group IV and the other three groups was due to the incidence of more 'right’ responses In this group (which had more practice). Thus the results of this experiment did not support the hypothesized importance of stimulus stability for postremity, arid also provided an analysis which showed its successful predictions were coincident with repetition of ‘right' responses. This repetition of 'right’ responses could be predicted by many theories. The validity of postremity as a practical predictor and as a theoretical concept was, within the limitations of this experiment, questioned.

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