Auditory habituation is revented in the background sound of 4-kHz pure tone : A magnetoencephalography study.

Abstract

Auditory evoked magnetic field (AEF) is gradually attenuated as the number of presentation of auditory stimuli increases. The attenuation of AEF is auditory habituation, and is prevented in the condition where a noise exists in the background. In this study, we investigated whether the background sound of pure tone prevent the auditory habituation to repeating stimuli. Subjects were 17 normal hearing individuals. Auditory stimuli were 1-kHz tone bursts set at 30 dB SL with durations of 100 ms and inter-stimulus intervals of 1.9-2.l s. The background sounds were silent, 4-kHz pure tone presented set at 5 and 20 dB SL which were presented with 1-kHz tone bursts. N1m component of AEF induced by auditory stimuli was measured using 122-channel neuromagnetometer. As a result, N1m amplitudes induced by repeating auditory stimuli were gradually attenuated in the condition of silent background due to the auditory habituation. Meanwhile, the attenuation of N1m amplitude was small in the conditions of background sounds of 4-kHz pure tones at 5 and 20 dB SL, compared to the conditions of silent background. Moreover, the time course of N1m amplitudes was not different between the condition of background sound at 5 and 20 dB SL. These results suggested that the background sound of pure tone, independent of its intensity, drove the subject to unconsciously pay attention to repeating auditory stimuli without disturbing signal-to-noise ratio of them, or the neural process of the background pure tone continuously activated the auditory pathway and resulted in the prevention of auditory habituation.