Auditory stimulation
The participants used an MP3 to listen to sounds. For auditory stimulation using nature sounds, the insect sounds were played at 49.5 dB, which were purchased from Audiostock. This sound was recorded at about 3:00 a.m. at a riverside in Osaka in autumn. For auditory stimulation using city sounds, we used the sound of traffic at an intersection in Shibuya, Tokyo. We played the sound of a scramble intersection at 49.4 dB downloaded from the Sound Effects Lab website. Two sets of headphones (Audio-Technica ATH-M20x) were prepared. Hence, each participant could use one set of headphones. Two participants used one audio player at the same time with a two-way distribution cable. Therefore, the order of stimulus presentation was counterbalanced for each pair.