Nonlinear cochlear responses differ during selective and inattentive listening
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Previous studies have demonstrated that the magnitudes of otoacoustic emissions (OAEs) measured during behavioral tasks requiring attention were different from OAE magnitudes measured during tasks that did not require attention. The implication of these results is that the cognitive and perceptual demands of a task can affect the first neural stage of auditory processing—the sensory receptors themselves. However, the directions of the reported attentional effects have been inconsistent, the magnitudes of the observed differences always have been small, and comparisons across studies have been made difficult by significant procedural differences. In this study, we used a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring selective auditory attention (dichotic or diotic listening), or relative inattention. The results indicated statistically significant systematic differences in nSFOAE magnitudes within subjects, but opposite directions of effect across subjects. Differences in the nSFOAEs measured during the dichotic- and diotic-listening conditions suggested that cochlear responses differed in these two types of selective-listening tasks. Time constants measured from functions fitted to the nSFOAE responses indicated faster efferent effects during selective listening than during inattentive listening for the majority of subjects. Furthermore, measurements in brief silent intervals after the nSFOAE stimuli indicated weaker residual nSFOAE magnitudes during selective listening than during inattentive listening for every subject. This collection of findings supports the hypothesis that auditory attentional demands can modulate cochlear processing, presumably to the benefit of the listener.