Binaural Background Noise Enhances Neuromagnetic Responses from Auditory Cortex

Dawei Shen,Claude Alain,Bernhard Ross

doi:10.3390/sym13091748

Abstract

The presence of binaural low-level background noise has been shown to enhance the transient evoked N1 response at about 100 ms after sound onset. This increase in N1 amplitude is thought to reflect noise-mediated efferent feedback facilitation from the auditory cortex to lower auditory centers. To test this hypothesis, we recorded auditory-evoked fields using magnetoencephalography while participants were presented with binaural harmonic complex tones embedded in binaural or monaural background noise at signal-to-noise ratios of 25 dB (low noise) or 5 dB (higher noise). Half of the stimuli contained a gap in the middle of the sound. The source activities were measured in bilateral auditory cortices. The onset and gap N1 response increased with low binaural noise, but high binaural and low monaural noise did not affect the N1 amplitudes. P1 and P2 onset and gap responses were consistently attenuated by background noise, and noise level and binaural/monaural presentation showed distinct effects. Moreover, the evoked gamma synchronization was also reduced by background noise, and it showed a lateralized reduction for monaural noise. The effects of noise on the N1 amplitude follow a bell-shaped characteristic that could reflect an optimal representation of acoustic information for transient events embedded in noise.

Highlights

Auditory perception is determined by the ratio between the stimulus and noise levels rather than the absolute stimulus intensity [1,2,3]
We examined the effects of hemispheres and noise type on P1, N1, and P2 sound onset and gap responses in auditory cortex source activity and gamma oscillation
The main findings of this study were that N1 amplitudes increased when stimuli were embedded in low-level binaural noise compared to stimuli presented in quiet conditions

Summary

Introduction

Auditory perception is determined by the ratio between the stimulus and noise levels rather than the absolute stimulus intensity [1,2,3]. Background noise affects auditory perception dramatically and is commonly associated with reduced amplitudes and prolonged auditory-evoked responses [4,5,6]. Previous work about the effect of background noise on auditory-evoked responses focused on the N1 wave, the negative potential at about 100 ms after sound onset in the human electroencephalogram (EEG) and its equivalent in the magnetoencephalogram (MEG). A lowlevel background noise paradoxically yields an increase in the N1 amplitude when both the stimuli and noise were presented binaurally in MEG [10,11,12] and EEG studies [13,14,15]. In the study of Papesh, Billings and Baltzell [14], the noise-related increased in N1 amplitude recorded using EEG was more pronounced in binaural than monaural noise conditions

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Discussion

Conclusion