Simulating the contribution of medial olivocochlear efferents to amplitude-modulation unmasking in humans

Amplitude-modulation (AM) detection thresholds for a tonal carrier in noise are often improved by the presentation of a precursor [e.g., Wojtczak et al., JARO 20, 395–413 (2019)]. This phenomenon, AM unmasking, may reflect activation of the medial olivocochlear reflex (MOCR) by the precursor, which would reduce cochlear gain and enhance AM coding during the tone. However, evidence regarding the MOCR’s role in AM unmasking is mixed. We simulated AM unmasking using a new physiological model of the peripheral and subcortical auditory system that includes an MOCR. At all carrier sound levels (40–80 dB SPL), precursor noises enhanced neural representations of AM and improved AM detection thresholds in at least some tonotopic channels, consistent with a role for the MOCR in AM unmasking. At low levels, channels tuned near the carrier frequency were generally the most informative and exhibited the greatest AM unmasking. At high levels, the informative channels were tuned further (>0.5 octaves) from the carrier frequency, suggesting the use of “off-frequency listening.” Consistent with behavioral results, noise precursors produced more simulated AM unmasking than pure- or complex-tone precursors. These results suggest an important role for the MOCR in the perception of complex sounds. [Work supported by NIDCD F32 DC022143.]