Hearing tests
RION
Hearing ability of the right and left ears was measured by using an audiometer (Audiometer AA-79, RION Co., Ltd., Tokyo, Japan). Participants wore dedicated headphones in a quiet room and listened to acoustic pure-tone signals. If participants responded at 40 dB, the volume was lowered by 10–20 dB until no response was seen, and then the volume was gradually raised by 5 dB until participants responded. The volume level at which participants responded again was recognized as their hearing threshold. Besides, if there was no response at 40 dB, the volume was increased by 10–20 dB until a response was observed. Then, the volume was decreased by 10–20 dB until no response was seen, after that the volume was gradually increased by 5 dB until participants responded again. The volume level at which participants responded again was recognized as their hearing threshold. The same procedures were followed in order to measure and evaluate pure-tone air-conduction hearing thresholds at frequencies of 2000 Hz, 4000 Hz, 8000 Hz, 500 Hz, 250 Hz, and 125 Hz, in the order [