Department of Biophysics, School of Medicine, Koc University, Istanbul, Turkey.
Department of Biophysics, Faculty of Medicine, Hacettepe University, Ankara, Turkey.
Exp Brain Res. 2019 Aug;237(8):1931-1945. doi: 10.1007/s00221-019-05562-7. Epub 2019 May 20.
When two tones with slightly different frequencies are dichotically presented, binaural beats (BBs) are experienced. BBs resulting from the cycling change in interaural phase difference elicit electroencephalographic responses. Because they repeat at short periods, allowing poor recovery of the cortical responses, these steady-state responses have small amplitudes, and their various wave components intermingle and might mask each other. Using single-cycle BBs separated by relatively long inter-onset intervals would be a solution, but introducing a transient interaural frequency shift requires response subtraction which may not be acceptable for non-additive brain responses. The proposed stimulation method employs transient and monaurally subthreshold frequency shifts in opposite directions in the two ears to produce single-cycle BBs of a 250 Hz tone. These shifts are perceived as distinct BBs when presented dichotically, but remain subthreshold when presented monotically. Therefore, no frequency-shift response is elicited, and the specific BB response is obtained with no need for waveform subtraction. We recorded from 19 normal hearing participants the event-related potentials (ERPs) to single-cycle BBs and also to temporary diotic amplitude modulation (AM) with matched perceptual salience. The ERPs to single-cycle BBs presented at 2 s inter-onset intervals had N1-P2 responses with up to seven times larger amplitudes than the conventional steady-state BB responses in the literature. Significant differences were found between the scalp potential distributions of the N1 responses to BB and AM stimuli, suggesting that the cortical sites, where envelope-based level processing and temporal fine structure-based spatial processing of the stimulus take place, are not totally overlapped.
当两个略有不同频率的音调以双声道呈现时，会产生双耳节拍（BBs）。由于它们以短周期重复，使得皮质反应恢复不佳，这些稳态反应的幅度较小，其各种波成分交织在一起，可能相互掩盖。使用通过相对较长的间隔分开的单周期 BB 是一种解决方案，但引入瞬态耳间频率偏移需要响应相减，这对于非加性脑反应可能不可接受。所提出的刺激方法采用在两个耳朵中以相反方向进行的瞬态和单耳亚阈值频率偏移，以产生 250 Hz 音调的单周期 BB。当以双声道呈现时，这些偏移被感知为明显的 BB，但当以单声道呈现时仍然处于亚阈值。因此，不会引起频率偏移响应，并且可以获得特定的 BB 响应，而无需进行波形相减。我们从 19 名正常听力参与者记录了与单周期 BB 相关的事件相关电位（ERPs），以及与匹配感知显著性的临时双声道调幅（AM）。在 2 秒的间隔发作间隔下呈现的单周期 BB 的 ERPs 具有高达七倍于文献中常规稳态 BB 响应的 N1-P2 响应。BB 和 AM 刺激的 N1 反应的头皮电位分布存在显着差异，这表明基于包络的水平处理和基于刺激的时间精细结构的空间处理的皮质部位不完全重叠。
