A new method of discrimination between non-guilty and guilty subjects based on the autonomic response pattern in polygraph test

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The present research investigated a new method for discriminating non-guilty persons from guilty ones in polygraph test based on the autonomic response pattern. Electrodermal activity, respiration movement, and plethysmogram have been used as indices in polygraph test. However, electrodermal activity tends to be habituated and plethysmogram can not indicate the activity level of sympathetic nervous system precisely. We introduced normalized pulse volume (NPV) into polygraph test as a new autonomic index. NPV showed significant decrement in the critical than in the non-critical questions. The results confirmed that NPV was a sensitive index of the peripheral vascular tone. NPV was used as a reliable and valid autonomic index in later studies. For investigating correlation patterns of autonomic responses, we conducted factor analysis on responses induced by emotion-evoking stimuli. Three factors were extracted ; a factor of blood pressure and peripheral vessel, a factor of respiration am … More plitude and inter heartbeat interval, and a factor of electrodermal indices. This analysis showed that autonomic responses were patterned by physiological systems. We also found characteristic response changes in the critical question. We named these physiological changes "the critical-question pattern". The responses during the critical question of guilty subjects corresponded to the pattern, while the responses of non-guilty subjects did not. The results indicated that three information were useful to discriminate non-guilty subjects from guilty ones ; the number of significant differences, the percentage of the differences corresponded to the critical-question pattern, and the percentage of responses related to peripheral vascular resistance corresponded to the critical- question pattern. We examined the availability of latent class discrimination method for polygraph test. This new multivariate method conducted guilty/non-guilty discrimination based on how a given response follows the critical-question pattern in each physiological system. The performance of this method was better than other conventional multivariate analyses. Less