MRC-Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, CB2 7EF, UK.
J Assoc Res Otolaryngol. 2011 Dec;12(6):767-82. doi: 10.1007/s10162-011-0284-1. Epub 2011 Aug 9.
The frequency following response (FFR), a scalp-recorded measure of phase-locked brainstem activity, is often assumed to reflect the pitch of sounds as perceived by humans. In two experiments, we investigated the characteristics of the FFR evoked by complex tones. FFR waveforms to alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. In experiment 1, frequency-shifted complex tones, with all harmonics shifted by the same amount in Hertz, were presented diotically. Only the autocorrelation functions (ACFs) of the subtraction-FFR waveforms showed a peak at a delay shifted in the direction of the expected pitch shifts. This expected pitch shift was also present in the ACFs of the output of an auditory nerve model. In experiment 2, the components of a harmonic complex with harmonic numbers 2, 3, and 4 were presented either to the same ear ("mono") or the third harmonic was presented contralaterally to the ear receiving the even harmonics ("dichotic"). In the latter case, a pitch corresponding to the missing fundamental was still perceived. Monaural control conditions presenting only the even harmonics ("2 + 4") or only the third harmonic ("3") were also tested. Both the subtraction and the addition waveforms showed that (1) the FFR magnitude spectra for "dichotic" were similar to the sum of the spectra for the two monaural control conditions and lacked peaks at the fundamental frequency and other distortion products visible for "mono" and (2) ACFs for "dichotic" were similar to those for "2 + 4" and dissimilar to those for "mono." The results indicate that the neural responses reflected in the FFR preserve monaural temporal information that may be important for pitch, but provide no evidence for any additional processing over and above that already present in the auditory periphery, and do not directly represent the pitch of dichotic stimuli.
频率跟随反应（FFR）是一种头皮记录的相位锁定脑干活动测量方法，通常被认为反映了人类感知的声音音高。在两项实验中，我们研究了复音诱发的 FFR 的特征。对于每个极性的交替极性刺激，平均了 FFR 波形并相加以增强包络，或相减以增强时间精细结构信息。在实验 1 中，以相同赫兹数量移频的复音以对立体声呈现。只有减法 FFR 波形的自相关函数（ACF）在延迟方向上显示出与预期音高偏移相对应的峰。这种预期的音高偏移也存在于听觉神经模型输出的 ACF 中。在实验 2 中，2、3 和 4 谐波的谐波复合的分量要么呈现给同一个耳朵（“单声道”），要么第三个谐波呈现给接收偶数谐波的耳朵的对侧（“立体声”）。在后一种情况下，仍然可以感知到缺失基频的音高。仅呈现偶数谐波（“2 + 4”）或仅呈现第三个谐波（“3”）的单声道控制条件也进行了测试。减法和加法波形都表明：（1）“立体声”的 FFR 幅度谱类似于两个单声道控制条件的谱之和，并且缺乏基频和其他失真产物的峰，这些产物在“单声道”中可见，而在“立体声”中不可见；（2）“立体声”的 ACF 类似于“2 + 4”的 ACF，而与“单声道”的 ACF 不同。结果表明，FFR 中反映的神经反应保留了可能对音高很重要的单声道时间信息，但没有提供任何证据表明在听觉外围之外存在任何额外的处理，也不能直接表示立体声刺激的音高。
