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.

中文翻译：

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双耳背景噪声增强听觉皮层的神经磁反应

双耳低电平背景噪声的存在已被证明可以在声音开始后约 100 毫秒增强瞬态诱发的 N1 响应。N1 振幅的这种增加被认为反映了从听觉皮层到较低听觉中枢的噪声介导的传出反馈促进。为了验证这一假设，我们使用脑磁图记录了听觉诱发场，同时向参与者展示了双耳或单耳背景噪声中嵌入的双耳谐波复合音调，信噪比为 25 dB（低噪声）或 5 dB（较高噪声） . 一半的刺激在声音的中间包含一个间隙。在双侧听觉皮层中测量源活动。起始和间隙 N1 响应随着低双耳噪声而增加，但高双耳和低单耳噪声不影响 N1 振幅。P1 和 P2 开始和间隙响应始终被背景噪音减弱，噪音水平和双耳/单耳呈现显示出不同的效果。此外，诱发的伽马同步也被背景噪声降低，并且它显示出单声道噪声的侧向降低。噪声对 N1 振幅的影响遵循钟形特征，可以反映嵌入噪声的瞬态事件的声学信息的最佳表示。