Authors: David López Ramos¹; Iman Cadi¹; Emmanuel Ponsot¹
¹STMS Lab (CNRS / Ircam / Sorbonne Université)
Background: Aging is associated with cochlear synaptopathy (CS)—a loss of synapses between inner hair cells and auditory nerve fibers. Beyond affecting afferent encoding, CS may reduce the input to the medial olivocochlear (MOC) system, thereby influencing efferent control of cochlear gain. This study combined computational modeling and psychophysics to evaluate age-related CS effects on MOC-mediated gain reduction using a forward-masking task.
Method: Detection thresholds for a 2-kHz probe were measured alone or following a 400-ms noise precursor in young (yNH) and older normal-hearing (oNH) listeners. The precursor-induced threshold shift served as an estimate of MOC-mediated gain reduction. Computational simulations of the auditory periphery with MOC feedback were used to predict thresholds under varying precursor bandwidths and temporal-envelope characteristics.
Results: Simulations predicted that reduced auditory nerve input to the MOC system would decrease threshold shifts, particularly for narrowband precursors. However, behavioral results showed no significant group differences for narrowband precursors and, unexpectedly, significantly larger threshold shifts in oNH listeners for wideband precursors, regardless of temporal-envelope modulations.
Conclusion: The findings suggest that forward-masking estimates of cochlear gain reduction are not solely reflective of MOC activity and may be influenced by other age-related factors. These results highlight the need for future research to combine behavioral paradigms with objective measures of MOC function to more accurately isolate changes in the efferent control of cochlear gain.
