Binaural Background Noise Enhances Neuromagnetic Responses from Auditory Cortex

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.

Temporal deployment of attention in musicians: Evidence from an attentional blink paradigm

“…81 The results showed musical training and informative cues enhanced the N1 amplitude significantly at right frontal-central sites. Right hemispheric dominance for responses to auditory stimuli has been reported in both EEG and MEG studies, [82][83][84][85] and could be related to the location and orientation of the N1 sources. The N1 is known to be generated in auditory areas along the superior temporal gyrus (STG) 82,[86][87][88][89] with a source orientation often pointing toward the contralateral frontal scalp area.…”