Effects of the preference for acoustic stimuli on sleep quality

Since pharmacological treatment for sleep disorders has a risk of addiction, developments of non-pharmacological tools to enhance sleep are needed. Colored noise sounds characterized by the power spectrum, e.g., white, pink, brown, blue, and purple noises, have been used in some non-pharmacological sleep aids. Former reports showed that white and pink noises were effective for sleep, however the mechanisms how such noises promote sleep remain unknown. In this study, we proposed a hypothesis that effects of colored noises are depending on participants' auditory impressions and examined how each participant's preference for the noises affected sleep-quality indices (sleep latency and duration of slow-wave sleep (SWS)). Sleep states of each participant were examined by EEG in three conditions: (i) the most preferred and (ii) the least preferred noises for each subject, and (iii) no stimulation. Sleep experiments were started at 3:00PM in a soundproof room and the stimulus began to be presented at lights-out and continued for 60 min. In results obtained, there were no significant differences in the sleep quality indices among the three conditions. Since duration of the experiment may not be enough to observe the effect of the stimuli, further investigations are needed after reviewing the experimental conditions.