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Auditory task-dependent control of human cochlear responses to sound

Accurate sensory perception in noisy environments requires physiological mechanisms that reduce sensory interference. In the auditory system, it has been hypothesized that attentional control of cochlear responses to sound facilitates listening in noisy environments by modulating the effects of medial olivocochlear (MOC) efferent activity in the cochlea. However, conclusive support for this hypothesis has been elusive over the past 50 years. We investigated this issue using a novel experimental paradigm in which human subjects performed auditory tasks on transient sounds presented in acoustic noise, while we recorded click-evoked otoacoustic emissions (CEOAEs) in the task ear. CEOAEs are low-level sounds that are generated in the cochlea, recorded in the ear-canal and provide a non-invasive measure of the MOC effects on cochlear mechanical responses to sound. Our results show clear evidence that attending to transient sounds in noise caused an increase in MOC activity during the auditory task. MOC activity was greater on trials with correct responses compared to trials with incorrect responses, which provides evidence that the MOC activity brought about a perceptually beneficial change in cochlear operation. In addition, the task-dependent MOC activity scaled with auditory task difficulty and varied with task instructions. These results indicate the existence of a dynamic task-dependent interaction between the cochlea and the brain that has the function of optimizing cochlear operation to enhance auditory perceptual accuracy in noisy acoustic environments. Thesis Supervisor: John J. Guinan, Jr., Ph.D. Title: Professor of Otology and Laryngology, Harvard Medical School