Correlations between preference for nature sounds and physiological and psychological relaxation on humans

This study aimed to determine the differences in relaxation effects of bird sound on humans based on their preference. We used the song of Turdus pallidus and call of Corvus macrorhynchos as the "more-preferred" and "less-preferred" bird sounds, respectively, and recruited thirty-two male and female university students. Participants wore a physiological measurement device, sat on a chair, and took a three-minute break. They then followed these steps: (1) closed their eyes and rested for one min; (2) heard either the more-preferred or less-preferred bird sound for one min; and (3) opened their eyes and evaluated their feelings about the bird sound using questionnaires and a semantic differential (SD) method. After another three-minute break, the same process was repeated with a different sound. Heart rate and heart rate variability were continuously measured during the experiment. The more-preferred bird sound was accompanied by significant decreases in heart rate and LF/HF, and the decrease in LF/HF was greater than that observed for the less-preferred bird sound. Participants also reported higher ratings of comfort, relaxation, friendliness, fullness, interest, and preference. For the association between the participants' feelings and their physiological responses, a repeated measures correlation analysis showed that a stronger feeling of friendliness tended to be accompanied by a larger decrease in heart rate, although this association did not survive correction for multiple comparisons. These findings suggest that the more-preferred bird sound elicited greater psychological relaxation and changes consistent with physiological relaxation in some physiological indices.