Modeling individual differences in overshoot: Effects of age, hearing loss, and efferent feedback

Abstract

The detection of a short sinusoidal probe in simultaneous masking improves as the probe's onset is delayed from the masker's onset. This “overshoot” may be mediated by the medial olivocochlear (MOC) reflex, whose pathway includes spiral ganglion neurons (SGNs), olivocochlear neurons and the outer hair cells (OHCs). Overshoot was measured in younger adults with normal hearing, older adults with normal hearing, and older adults with hearing loss to test the hypothesis that overshoot decreases as components in the MOC reflex pathway are compromised. Overshoot was significantly reduced in older adults, but only those with hearing loss, which is consistent with overshoot depending primarily on the status of the OHCs and only minimally influenced by age-related reductions in SGNs. Thresholds measured when the probe was near the masker’s onset showed large differences across listeners, resulting in appreciable individual differences in overshoot. Simulations were generated from a computational model of the auditory system to quantify the contributions of cochlear hearing loss, MOC reflex strength, and detection efficiency to individual differences in overshoot. Preliminary results suggest that cochlear hearing loss and detection efficiency explain the largest portion of the variance in overshoot among adults with normal and impaired hearing. [Work supported by NIH/NIDCD.]