Accumulation of self-reported restorative effects of natural sounds: A seven-day intervention indoors

This study investigated the restorative effects of repeated listening to natural sounds indoors in real-life settings. Previous studies have mainly been cross-sectional and laboratory studies. We designed an online field experiment lasting seven days, in which we assigned 166 university students to one of four intervention groups: (1) listening to natural sounds, (2) sitting in silence (i.e., another means of restoration), (3) reading news online (i.e., a prevalent but not necessarily restorative activity), or (4) no intervention (i.e., the control). Self-reported restorative experience was measured both before and after the daily intervention (but once a day in the no-intervention group), and the weekly-measured perceived stress and state mindfulness were assessed at the beginning and end of the intervention week. Linear hypothesis tests based on a linear mixed-effects model (LMM) showed that, at the day level, natural sounds were the most restorative, followed by silence, while reading news proved not to be restorative. In addition, the daily restorative effect of natural sounds was carried over to later days and its seven-day accumulation was half as great as the general daily restorative effect, although the within-day pre-post change ostensibly diminished over time. An ANCOVA and paired t-tests revealed that a reduction in the weekly-measured perceived stress and an increase in the weekly-measured mindfulness took place after listening to natural sounds or sitting in silence, with the former intervention type having stronger effects, aligning with the results for the restorative experience. Our findings suggest that the carryover effect of repeated listening to natural sounds for psychological restoration may more than compensate for the diminishing returns in within-day pre-post changes over the course of a week.