Two experiments examined whether focused attention toward a visual display would alter the sensory transmission properties of the human auditory nerve and brainstem centers to irrelevant auditory tone pips. In the first experiment, 16 subjects either listened to 1000 Hz, 50dB SL tone pips presented binaurally at 10/sec (“Listen”), or mentally counted letters flashed rapidly on a screen (“Look”). The auditory brainstem potentials recorded from the vertex were averaged on‐line in groups of 500 with a 10‐msec sweep and a bandpass of 150–1500 Hz. Results indicated that during the “Look” trials, Wave 5 generated from the inferior colliculus (7.322 msec latency) was significantly reduced in amplitude by 16.4% and increased in latency by 27 μsec. A second experiment with 8 subjects demonstrated that the effects of attention are limited to the auditory nerve component when using 8000 Hz stimuli but are significant for both the auditory nerve and collicular components when a mid‐frequency (2000 Hz) tone pip is used. These results suggest that during concentrated attention toward visual stimuli, irrelevant auditory stimuli may be attenuated at a peripheral level possibly through the action of the efferent olivocochlear bundle.

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.

The augmenting or reducing of flash-evoked potentials in paralyzed cats was significantly correlated with their previously videotaped behaviors. Augmenting reducing was due to alterations in cortical rather than subcortical responsiveness, and was duplicated by increasing cortical arousal by means of reticular stimulation while the animal was exposed to visual stimuli of constant intensity. Brainstem activation of cortical inhibition may underlie the behavioral results as well as the results obtained with the evoked potentials.

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