Mechanisms of auditory enhancement in younger and older adults.

Auditory enhancement (AE), a perceptual phenomenon reflecting listeners' ability to use sequential spectral contrasts to improve detection and identification of target sounds, is reduced by hearing loss. Effects of advancing age on AE are less clear, mainly because the mechanisms underlying the phenomenon are not well understood. One of the most common explanations for AE, in terms of adaptation of inhibition, predicts age-related reductions of AE due to reductions of neural inhibition. In this study, AE was measured for younger and older adults using a target-detection task for unmodulated and amplitude-modulated pure-tone targets surrounded by an inharmonic-complex masker. The masker-target complex followed a precursor comprising either masker components alone or both masker and target components. The results show that a release from informational masking related to grouping between simultaneous target and masker components is an important, but not the sole, contributor to AE. For an amplitude-modulated target, AE was reduced in older compared to the younger group and its magnitude was not correlated with hearing thresholds. The findings are consistent with the idea that age-related reductions of AE magnitude are due to reduced neural inhibition and may contribute to age-related difficulties with speech-in-noise perception.