Modeling auditory enhancement: Efferent control of cochlear gain can explain level dependence and effects of hearing loss

The role of medial olivocochlear (MOC) efferent gain control in auditory enhancement (AE) was investigated using a subcortical auditory model. AE refers to the influence of a precursor on detectability of targets. The absence (or presence) of a precursor component at the target frequency enhances (or suppresses) detection under simultaneous masking conditions. Furthermore, the enhanced target under simultaneous masking acts as a stronger forward masker for a delayed probe tone, known as AE under forward masking. Psychoacoustic studies of AE report findings that challenge conventional expectations, and the underlying mechanisms remain unclear. For instance, listeners with hearing impairment have AE under simultaneous masking but not forward masking [Kreft, Wojtczak, and Oxenham (2018). J. Acoust. Soc. Am. 143(2), 901-910; Kreft and Oxenham (2019). J. Acoust. Soc. Am. 146(5), 3448-3456], whereas listeners with normal hearing have level-dependent AE under forward masking [Kreft and Oxenham (2019). J. Acoust. Soc. Am. 146(5), 3448-3456]. Our model with MOC efferent gain control successfully replicated these findings. In contrast, a model without efferent gain control failed to capture these effects, supporting the hypothesis that MOC-mediated cochlear gain modulation may play a role in AE and its alteration by hearing loss.