Psychophysiological responses to heteromodal stimulation



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This study was undertaken to investigate peripheral autonomic responses to heteromodal stimuli presented alone and in combination. It was designed to clarify and extend the results of previous psychophysiological research on this topic. The experiment involved recording heart rate, respiration rate, and skin resistance whild subjects attended to mild stimuli. The stimuli were a clacking sound and a flashing light. Each stimulus was presented alone for thirty seconds, and each stimulus was also imposed on the other fifteen seconds after it had begun. It was hypothesized that imposing light on sound would suppress the ongoing response to the sound, and that this would also occur for the reverse sequence; that is, sound imposed on light. It was also hypothesized that response levels for light presented in the presence of sound would be lower than response for light alone, and that responses to sound in the presence of light would be lower than responses to sound alone. The first hypothesis was derived from previous psychophysiological research on the topic of heteromodal stimulation, and the second hypothesis was derived from psychophysical and other research on the topic. The data appeared to partially support both hypotheses. Response levels for light imposed on sound were lower than those for immediately proceeding sound alone, but this did not occur when sound was imposed on light. Also, the response levels for sound in the presence of light were lower than response levels for sound alone, but response levels for light in the presence of sound were no different than those for light alone. Although these results were statistically significant, and agreed with previous research, it was concluded that the hypotheses were not adequately tested due to the mildness of the stimuli used. Adaptation to the stimuli proceeded very rapidly, and there was little ongoing response when the second stimulus was begun; therefore hypothesis one could not be tested. The results for hypothesis two allowed two alternative explanations, one favorable to the hypothesis and one based on the weakness of the stimuli, and no information was available to choose between the alternatives. Therefore, hypothesis two was not adequately tested. The results of the experiment did indicate that peripheral autonomic measures were useful measures for studies of heteromodal stimulation, and also suggested that future investigations use stimuli which result in responses which are neither maximal nor minimal.