The acoustic reflex threshold in relation to noise-induced hearing loss.

In 100 consecutive cases with severe noise-induced hearing loss, pure-tone threshold measurements revealed symmetric hearing losses with maximum shifts at 4000 and 6000 Hz. Acoustic reflex measurements showed that few patients had an elevated pathologic reflex threshold. In contrast, we found a depressed acoustic reflex sensation level (i.e., the difference, in decibels, between pure-tone threshold and acoustic reflex threshold) suggesting a cochlear localization of the injury. Consequently, the probability of retro-cochlear involvement was small, or the cochlear component dominated the retro-cochlear one. The relation between the absence of the acoustic reflex and the degree of hearing loss showed that even at a pure-tone threshold of 80 dB HL, 50% of the ears still had an elicitable acoustic reflex. Statistical analysis yielded a significant correlation between acoustic reflex sensation level and speech discrimination, but no such correlation between acoustic reflex threshold and speech discrimination. We suggest that acoustic reflex sensation level should be a complement to the acoustic reflex threshold in order to distinguish between different localizations of sensorineural hearing losses.