Department of Speech Language Hearing Sciences, Purdue University, 1353 Heavilon Hall, 500 Oval Drive, West Lafayette, IN 47907-2038, USA.
Hear Res. 2011 May;275(1-2):110-9. doi: 10.1016/j.heares.2010.12.008. Epub 2010 Dec 16.
Psychoacoustic studies have shown that complex tones containing resolved harmonics evoke stronger pitches than complex tones with only unresolved harmonics. Also, unresolved harmonics presented in alternating sine and cosine (ALT) phase produce a doubling of pitch. We examine here whether the temporal pattern of phase-locked neural activity reflected in the scalp recorded human frequency following response (FFR) preserves information relevant to pitch strength, and to the doubling of pitch for ALT stimuli. Results revealed stronger neural periodicity strength for resolved stimuli, although the effect of resolvability was weak compared to the effect observed behaviorally; autocorrelation functions and FFR spectra suggest a different pattern of phase-locked neural activity for ALT stimuli with resolved and unresolved harmonics consistent with the doubling of pitch observed in our behavioral estimates; and the temporal pattern of neural activity underlying pitch encoding appears to be similar at the auditory nerve (auditory nerve model response) and the rostral brainstem level (FFR). These findings suggest that the phase-locked neural activity reflected in the scalp recorded FFR preserves neural information relevant to pitch that could serve as an electrophysiological correlate of the behavioral pitch measure. The scalp recorded FFR may provide for a non-invasive analytic tool to evaluate neural encoding of complex sounds in humans.
心理声学研究表明，包含可分辨谐波的复音比只有不可分辨谐波的复音能引起更强的音高。此外，以正弦和余弦（ALT）交替相位呈现的未解决谐波会使音高加倍。我们在这里研究头皮记录的人类频率跟随反应（FFR）中反映的锁相神经活动的时变模式是否保留与音强相关的信息，以及与 ALT 刺激的音高加倍相关的信息。结果表明，可分辨刺激的神经周期性强度更强，尽管与行为观察到的效果相比，可分辨性的效果较弱；自相关函数和 FFR 谱表明，对于具有可分辨和不可分辨谐波的 ALT 刺激，锁相神经活动的模式不同，与我们在行为估计中观察到的音高加倍一致；并且，音高编码的神经活动的时变模式在听神经（听神经模型反应）和颅脑干水平（FFR）似乎相似。这些发现表明，头皮记录的 FFR 中反映的锁相神经活动保留了与音高相关的神经信息，这些信息可以作为行为音高测量的电生理相关性。头皮记录的 FFR 可能为评估人类复杂声音的神经编码提供一种非侵入性分析工具。
