Dolphin W F, Chertoff M E, Burkard R
Department of Biomedical Engineering, Boston University, Massachusetts 02215.
J Acoust Soc Am. 1994 Oct;96(4):2225-34. doi: 10.1121/1.411382.
Two-tone (TT) and sinusoidally amplitude-modulated (SAM) signals, although differing in spectra, are both periodic; the period corresponds to the difference between the two frequencies (f2,1 = f2-f1) in the former and to the frequency of the modulation tone (fmod) in the latter. Here the results of a study comparing the steady-state electrophysiologic responses to TT and SAM stimuli recorded from Nembutal-anesthetized Mongolian gerbils are reported. In the first experiment a modulation rate transfer function (MRTF) was obtained for each stimulus type by setting the SAM carrier frequency (fc) and f1 of the TT signal at the same frequency while fmod and f2,1 were covaried. MRTFs were obtained for f1s and fcs of 1, 3, and 5 kHz, with envelopes which varied between 50 and 500 Hz in 50-Hz increments. Stimuli were presented at 75 dB peak sound-pressure level (pSPL). Responses to the two stimulus types yielded MRTFs which were very similar and generally low pass in shape. In the second experiment responses to the TT and SAM signals were recorded in the presence of a continuous interfering tone of 85-dB pSPL which was varied between 650 Hz and 3 kHz. In these experiments a maximum reduction in the response to the TT and SAM signals, measured at f2,1 and fmod as well as at fc and f1, occurred within a narrow frequency band above the frequency of the probe carrier and a broader region of reduced response extending to higher frequencies. This reduction in response was asymmetrical, spreading more to high than to low frequencies. The similarity of both MRTFs and interference response patterns supports the view that the envelope following responses to TT and SAM stimuli are manifestations of the same nonlinear phenomena.
双音（TT）信号和正弦调幅（SAM）信号，尽管频谱不同，但都是周期性的；前者的周期对应于两个频率之间的差值（f2,1 = f2 - f1），后者的周期对应于调制音的频率（fmod）。在此报告一项研究结果，该研究比较了从戊巴比妥麻醉的蒙古沙鼠记录到的对TT和SAM刺激的稳态电生理反应。在第一个实验中，通过将SAM载波频率（fc）和TT信号的f1设置为相同频率，同时使fmod和f2,1协变，为每种刺激类型获得了调制率传递函数（MRTF）。针对1、3和5 kHz的f1和fc获得了MRTF，其包络在50至500 Hz之间以50 Hz的增量变化。刺激以75 dB峰值声压级（pSPL）呈现。对这两种刺激类型的反应产生了非常相似且通常呈低通形状的MRTF。在第二个实验中，在存在85 dB pSPL的连续干扰音的情况下记录对TT和SAM信号的反应，该干扰音在650 Hz至3 kHz之间变化。在这些实验中，在高于探测载波频率的窄频带内以及延伸到更高频率的更宽反应降低区域内，测量到的对TT和SAM信号的反应在f2,1和fmod以及fc和f1处出现最大降低。这种反应降低是不对称的，向高频扩展的程度大于向低频扩展的程度。MRTF和干扰反应模式的相似性支持了这样一种观点，即对TT和SAM刺激的包络跟随反应是同一非线性现象的表现。
