Suppression of the auditory frequency following response during visual attention

Frequency-following responses (FFRs) were recorded from unanesthetized cats with electrodes chronically implanted in the cochlear nucleus and on the round window. Tone bursts of different frequencies (irrelevant stimuli) were presented repetitively (85 dB SPL, 1/sec) as background before, during, and after the presentation of a visual discrimination task (relevant stimuli) which attempted to alter the attentive state of the animals. The mean peak-to-peak amplitudes of the FFRs from the cochlear nucleus were significantly reduced in amplitude during attention to the visual discrimination stimuli when compared with the amplitudes of the pretest- and posttest-control periods. However, at the round window (cochlear microphonic) no significant differences in amplitude were observed for the same periods. Although the amplitudes of the FFRs were reduced in amplitude at all frequencies during visual attention, much greater suppression occurred at the middle frequencies (700-2000 Hz) than at higher or lower frequencies. These data suggest that during visual attention the FFRs are attenuated by a central inhibitory mechanism.