Presenting changes in acoustic features synchronously to respiration alters the affective evaluation of sound

Synchronization of respiration to cyclic auditory stimuli is a well-observed phenomenon and known to have an effect on affective evaluation of the presented sound. However, no studies have separated the effect of the change in respiratory movement itself and that when there is synchrony between respiration and sound. In this study, we used a system that can change the acoustic features synchronously with the respiration phase and directly investigated the effect the synchrony has on affective ratings without changing respiratory movements. An acoustic stimulation was presented where the sound intensity (SI) or fundamental frequency (F0) was modulated in response to the participant's respiration phase. Affective evaluations of the acoustic stimuli were made by using the Self-Assessment Manikin (SAM). The experiments compared synchronous and asynchronous conditions. In the synchronous condition, SI (or F0) was increased with inhalation (decreased with exhalation) or decreased with inhalation (increased with exhalation). In the asynchronous condition, a sound identical to that presented in the synchronous condition was replayed. The participants evaluated sounds that were acoustically the same but where the temporal relationship differed between respiration and the acoustic features. In our results, significantly higher arousal ratings were observed when the change in SI and respiration (inhalation or exhalation) was synchronous and when the increase in F0 and inhalation was synchronous. This suggests that the synchronous phenomenon between respiration and auditory stimuli can play a critical role in affective evaluation.