Intrinsic differences in hearing performances between ears revealed by the asymmetrical shooting posture in the army.

Left ear noise-induced hearing losses are dominant in the army. The common explanation is the asymmetrical effect of the shooting posture. However, firm evidence to support this possibility is still lacking. In the French army shooters, eye preference rather than hand preference for shooting determines the side of shooting and hence the ear more exposed to noise. To test whether left-right asymmetry of hearing thresholds really relates to the shooting posture, we analyzed audiograms from 644 officers of the infantry and artillery branches. The interaural differences reached 7 dB for right-eyed subjects, and less, about 5 dB, for left-eyed subjects at 6-7 kHz, both with disadvantage for the left ear. In contrast, hearing thresholds of both groups in the low frequency range were significantly better for left ears. Our results suggest each ear has different intrinsic characteristics. The right cochlea might be a less sensitive but more robust sensor than the left cochlea, which might be a finer sensor but more sensitive to noise.