Evidence for adaptive plasticity in elderly monaural hearing aid users.

Hearing aids can induce perceptual changes in some elderly listeners but few studies have investigated physiological changes in this population. Loudness discomfort levels and acoustic reflex thresholds were measured in long-term users of a single hearing aid. The results show an asymmetry of +2 to +9 dB between ears in the sound level that (i) causes loudness discomfort and (ii) elicits a reflex contraction of the middle ear muscles. The elevation of the acoustic reflex threshold occurs in the ear with hearing aid experience, irrespective of the ear of stimulation. Therefore, there is evidence of adaptive plasticity and this can be measured at the level of the auditory brainstem.