Aiken Steven J, Picton Terence W
Rotman Research Institute, Baycrest Centre for Geriatric Care, University of Toronto, Toronto, Canada.
Ear Hear. 2008 Apr;29(2):139-57. doi: 10.1097/aud.0b013e31816453dc.
To evaluate the response of the human auditory cortex to the temporal amplitude-envelope of speech. Responses to the speech envelope could be useful for validating the neural encoding of intelligible speech, particularly during hearing aid fittings--because hearing aid gain and compression characteristics for ongoing speech should more closely resemble real world performance than for isolated brief syllables.
The speech envelope comprises energy changes corresponding to phonemic and syllabic transitions. Envelope frequencies between 2 and 20 Hz are important for speech intelligibility. Human event-related potentials were recorded to six different sentences and the sources of these potentials in the auditory cortex were determined. To improve the signal to noise ratio over ongoing electroencephalographic recordings, we averaged the responses over multiple presentations, and derived source waveforms from multichannel scalp recordings. Source analysis led to bilateral, symmetrical, vertical, and horizontal dipoles in the posterior auditory cortices. The source waveforms were then cross-correlated with the low frequency log-envelopes of the sentences. The significance and latency of the maximum correlation for each sentence demonstrated the presence and latency of the brain's response. The source waveforms were also cross-correlated with a simple model based on a series of overlapping transient responses to stimulus change (the derivative of the log-envelope).
Correlations between the log-envelope and vertical dipole source waveforms were significant for all sentences and for all but one of the participants (mean r = 0.35), at an average delay of 175 (left) to 180 (right) msec. Correlations between the transient response model (P1 at 68 msec, N1 at 124 msec, and P2 at 208 msec) and the vertical dipole source waveforms were detected for all sentences and all participants (mean r = 0.30), at an average delay of 6 (right) to 10 (left) msec.
These results show that the human auditory cortex either directly follows the speech envelope or consistently reacts to changes in this envelope. The delay between the envelope and the response is approximately 180 msec.
评估人类听觉皮层对语音时间幅度包络的反应。对语音包络的反应可能有助于验证可理解语音的神经编码，特别是在助听器验配过程中——因为对于持续语音的助听器增益和压缩特性应比孤立的简短音节更接近真实世界的表现。
语音包络包含与音素和音节转换相对应的能量变化。2至20赫兹之间的包络频率对语音可懂度很重要。记录了人类与事件相关的电位，针对六个不同的句子，并确定了这些电位在听觉皮层中的来源。为了提高相对于持续脑电图记录的信噪比，我们对多次呈现的反应进行平均，并从多通道头皮记录中导出源波形。源分析导致双侧、对称、垂直和水平偶极子出现在后听觉皮层。然后将源波形与句子的低频对数包络进行互相关。每个句子最大相关性的显著性和潜伏期证明了大脑反应的存在和潜伏期。源波形还与基于对刺激变化的一系列重叠瞬态反应（对数包络的导数）的简单模型进行互相关。
对数包络与垂直偶极子源波形之间的相关性在所有句子以及除一名参与者外的所有参与者中均显著（平均r = 0.35），平均延迟为175（左）至180（右）毫秒。瞬态反应模型（68毫秒处的P1、124毫秒处的N1和208毫秒处的P2）与垂直偶极子源波形之间的相关性在所有句子和所有参与者中均被检测到（平均r = 0.30），平均延迟为6（右）至10（左）毫秒。
这些结果表明，人类听觉皮层要么直接跟随语音包络，要么始终对该包络的变化做出反应。包络与反应之间的延迟约为180毫秒。
