Effects of parametric speaker sound on physiological functions during mental task.

In recent years, parametric speakers have been used in various circumstances. However, nothing has yet been demonstrated about the safety of parametric speakers for the human body. Therefore, we studied their effects on physiological functions. Nine male subjects participated in this study. They completed three consecutive sessions: a 20-min quiet period as a baseline, a 45-min mental task period with a general speaker or a parametric speaker, and a 20-min recovery period. We measured electrocardiogram (ECG), photoplethysmogram (PTG), electroencephalogram (EEG), blood pressure (BP), and baroreflex sensitivity (BRS). Two experiments, one with a general speaker (the general condition), the other with a parametric speaker (the parametric condition), were conducted at the same time of day on separate days. To examine the effects of the parametric speaker, a two-way repeated measures ANOVA (speaker factor and time factor) was conducted. We found that sympathetic nervous activity and second derivative of PTG in task period and recovery period during the parametric condition were significantly lower than those indications during the general condition. Furthermore, Δ parasympathetic nervous activity during the parametric condition in task period and recovery period tended to be smaller than that during the general condition. The results suggested that the burden of the parametric speaker is lower than that of the general speaker for physiological functions, especially those of the cardiovascular system. Furthermore, we verified that the reaction time with the parametric speaker is shorter than that with the general speaker.