Loudness and sound category: Their distinct roles in shaping perceptual and physiological responses to soundscapes

Abstract When compared to 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 (SNS) activity as well as the pleasantness and eventfulness of the soundscape across two passive and active listening tasks in (N = 25) healthy subjects. 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 analysed by taking the mean level across the stimulus epoch, and also by quantifying its dynamic. We found that mean SCR was modulated by loudness only. SCR rise-time (a measure of speed of the skin response) correlated significantly with soundscape pleasantness and eventfulness for nature and mechanical sounds. This study highlights the importance of considering both loudness level and sound category in evaluating the perceptual soundscape, highlighting SCR as a valuable tool for such assessments. Impact statement Loud mechanical sounds are considered more unpleasant than nature sounds. This study examined whether loudness alone causes this effect or if the type of sound (e.g., mechanical vs. Nature) also plays a role. By measuring skin conductance reflecting the automatic and unconscious activation of the body’s autonomic system, we found that physical reactions are driven by loudness but also correlate with the listener’s judgement of the pleasantness and eventfulness (describing the perceived level of activity or stimulation) of a soundscape.