Abstract
Previous studies on changes of respiration during detection of deception revealed that decreases in respiration line length (RLL) (Timm, 1982) and decreases in respiration speed (Adachi & Suzuki, 1994) were the most sensitive markers of deception. Those studies also suggested that typical changes during deception are inhibitory breathing. However, because most of previous studies only analyzed respiratory movements and did not measure ventilation, it is still unclear whether these two indices, RLL and respiration speed, reflect the aspects of ventilation. In this study, therefore, we continuously monitored ventilation by using pneumotachograph under a mock crime situation to clarify the relationship between the two indices of respiratory movements and ventilation. Analyses of ventilatory data obtained from thirty male and female undergraduate subjects revealed that both RLL and respiratory speed reflect respiratory flow rate. Further analysis showed that expiratory flow rate is more sensitive to deception than inspiratory flow rate. Decreases in expiratory flow rates to critical items in the guilty knowledge test were significantly larger than that to non-critical items. Results obtained in this study clearly suggested that effects of deception are revealed in the expiratory phase of breathing, and that they inhibit expiratory flow rate.
