The role of efferent inhibition in human auditory attention: an examination of the auditory brainstem potentials.

This study examined whether the efferent olivocochlear bundle (OCB) functions to attenuate irrelevant auditory stimuli during visual attention. Subjects either counted 8000 Hz, 50 dB SL target tone pips, or target letters flashed rapidly on a visual display. The target stimuli were randomly interspersed among nontarget stimuli to prevent ther subjects anticipating their occurrence (Naatanen, 1975). The auditory brainstem potentials were tape recorded for separate analyses of the target and nontarget tone pips. The nontarget tone pips were not significantly affected suggesting they were attenuated in the auditory task (intramodal effect) as well as during the visual task. During focused visual attention, the auditory nerve component to the target tone pips was significantly reduced in amplitude by 37.4% and increased in latency by 90 musec. Wave V generated partially from the inferior colliculus was also reduced in amplitude by 12.9%; however, this decrement, was not statistically significant. The use of 8000 Hz tone pips and random target presentation precluded middle ear muscle contractions producing these results. It was concluded that the efferent OCB which synapses on and inhibits the hair cells and axons within the cochlea may function during visual attention by attenuating irrelevant acoustic stimuli.