Left-right asymmetry in the human response to experimental noise exposure. II. Pre-exposure hearing threshold and temporary threshold shift at 4 kHz frequency.

The repeatedly noted average inferiority of the left ear (or superiority of the right ear) in epidemiological surveys at frequencies most susceptible to noise damage has not been experimentally confirmed. Twenty-eight non-shooting young adults were exposed binaurally to broad-band noise for a maximum of 8 h in strictly symmetrical laboratory conditions. The left and right hearing thresholds of each individual were monitored during short interruptions in the exposure. The average interaural hearing threshold difference became statistically significant during the exposure, the left ear being worse than right. The negative correlation found between the pre-exposure threshold level and the temporary threshold shift (TTS) was more marked in the left than in the right ear. In conclusion a hypothesis is presented: a good hearing threshold level in the right ear seems to be better protected from noise-induced temporary threshold shift than a good hearing threshold in the left ear.