Loudness and Sound Category: Their Distinct Roles in Shaping Perceptual and Physiological Responses to Soundscapes.

When compared with nature sounds, exposure to mechanical sounds evokes higher levels of perceptual and physiological arousal, prompting the recruitment of attentional and physiological resources to elicit adaptive responses. However, it is unclear whether these attributes are solely related to the sound intensity of mechanical sounds, since in most real-world scenarios, mechanical sounds are present at high intensities or if other acoustic or semantic factors are also at play. We measured the skin conductance response (SCR), reflecting sympathetic nervous system activity as well as the pleasantness and eventfulness of the soundscape across two passive and active listening tasks in healthy subjects (N = 25; 14 females, 11 males). The auditory stimuli were divided into two categories, nature and mechanical sounds, and were manipulated to vary in three perceived loudness levels. As expected, we found that the sound category influenced perceived soundscape pleasantness and eventfulness. SCR was analyzed by taking the mean level across the stimulus epoch and also by quantifying its dynamics. We found that mean SCR was modulated by loudness only. SCR rise-time (a measure of the time it takes the skin response to increase from the baseline to its maximum value) correlated significantly with soundscape pleasantness and eventfulness for nature and mechanical sounds. This study highlights the importance of considering both the loudness level and sound category in evaluating the perceptual soundscape, and it identifies SCR as a valuable tool for such assessments.