School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907-2038, USA.
Hear Res. 2012 Oct;292(1-2):26-34. doi: 10.1016/j.heares.2012.08.001. Epub 2012 Aug 14.
Pitch experiments aimed at evaluating temporal pitch mechanism(s) often utilize complex sounds with only unresolved harmonic components, and a low-pass noise masker to eliminate the potential contribution of audible distortion products to the pitch percept. Herein we examine how: (i) masker induced reduction of neural distortion products (difference tone: DT; and cubic difference tone: CDT) alters the representation of pitch relevant information in the brainstem; and (ii) the pitch salience is altered when distortion products are reduced and/or eliminated. Scalp recorded brainstem frequency following responses (FFR) were recorded in normal hearing individuals using a complex tone with only unresolved harmonics presented in quiet, and in the presence of a low-pass masker at SNRs of +15, +5, and -5 dB. Difference limen for F0 discrimination (F0 DL) was obtained in quiet and in the presence of low-pass noise. Magnitude of DT components (with the exception of components at F0 and 2F0), and the CDT components decreased with increasing masker level. Neural pitch strength decreased with increasing masker level for both the envelope-related (FFR(ENV)) and spectral-related (FFR(SPEC)) phase-locked activity. Finally, F0 DLs increased with decreasing SNRs suggesting poorer F0 discrimination with reduction of the distortion products. Collectively, these findings support the notion that both DT and CDT, as reflected in the FFR(ENV) and FFR(SPEC), respectively, influence both the brainstem representation of pitch relevant information and the pitch salience of the complex sounds.
评估时域音高机制的音高实验通常使用只有未解析谐波分量的复杂声音，并使用低通噪声掩蔽器消除可听失真产物对音高感知的潜在贡献。本文研究了以下两个问题：(i)掩蔽器引起的神经失真产物（差频：DT；和立方差频：CDT）减少如何改变脑干中与音高相关信息的表示；以及 (ii) 当失真产物减少和/或消除时，音高显著性如何改变。使用仅具有未解析谐波的复音在安静环境中和在 SNR 为+15、+5 和-5dB 的低通掩蔽器存在下，记录正常听力个体的头皮记录脑干频率跟随反应（FFR）。在安静环境中和在低通噪声存在下获得 F0 辨别差异阈限（F0 DL）。随着掩蔽器水平的增加，DT 分量（除了 F0 和 2F0 处的分量）和 CDT 分量减小。对于与包络相关的（FFR(ENV))和与频谱相关的（FFR(SPEC))锁相活动，神经音高强度随着掩蔽器水平的增加而降低。最后，随着 SNR 的降低，F0 DL 增加，这表明随着失真产物的减少，F0 辨别能力变差。总之，这些发现支持这样一种观点，即 DT 和 CDT 都分别反映在 FFR(ENV)和 FFR(SPEC)中，影响与音高相关信息的脑干表示和复杂声音的音高显著性。
