Effects of auditory attention on otoacoustic emissions

In humans, auditory efferent control of the cochlea has been implicated in sharpening of frequency tuning, improved detection of signals in noise, and the ability to switch the focus of auditory attention. However, it remains unknown whether the modulation of efferent activity during an auditory attention task depends on the degree of task difficulty. This study aimed to compare the suppression of otoacoustic emissions (OAEs), an objective measure of auditory efferent activation, during a lexical decision task with varying degrees of difficulty, compared with passive auditory listening. Ten normal-hearing 18-35 year-olds were assessed using monosyllabic words and non-words presented in a natural or noise-vocoded (less intelligible) condition. The participants were instructed to press a button every time they heard a non-word. Simultaneously, click evoked-OAEs were obtained from the contralateral ear to the speech stimuli with a probe in the external ear canal. Preliminary results showed that OAEs amplitudes were suppressed during the lexical decision tasks relative to passive listening. In addition, an effect of task difficulty was found, whereby the less intelligible condition showed stronger suppression. These data suggest that the auditory efferent system is recruited through auditory attention, and that this may play a role in speech perception.