Wiegrebe Lutz, Meddis Ray
Dept. Biologie II, Universität München, Luisenstrasse 14, 80333 München, Germany.
J Acoust Soc Am. 2004 Mar;115(3):1207-18. doi: 10.1121/1.1643359.
The nature of the neural processing underlying the extraction of pitch information from harmonic complex sounds is still unclear. Electrophysiological studies in the auditory nerve and many psychophysical and modeling studies suggest that pitch might be extracted successfully by applying a mechanism like autocorrelation to the temporal discharge patterns of auditory-nerve fibers. The current modeling study investigates the possible role of populations of sustained chopper (Chop-S) units located in the mammalian ventral cochlear nucleus (VCN) in this process. First, it is shown that computer simulations can predict responses to periodic and quasiperiodic sounds of individual Chop-S units recorded in the guinea-pig VCN. Second, it is shown that the fundamental period of a periodic or quasiperiodic sound is represented in the first-order, interspike interval statistics of a population of simulated Chop-S units. This is true across a wide range of characteristic frequencies when the chopping rate is equal to the f0 of the sound. The model was able to simulate the results of psychophysical studies involving the pitch height and pitch strength of iterated ripple noise, the dominance region of pitch, the effect of phase on pitch height and pitch strength, pitch of inharmonic stimuli, and of sinusoidally amplitude modulated noise. Simulation results indicate that changes in the interspike interval statistics of populations of Chop-S units compare well with changes in the pitch perceived by humans. It is proposed that Chop-S units in the ventral cochlear nucleus may play an important role in pitch extraction: They can convert a purely temporal pitch code as observed in the auditory nerve into a temporal place code of pitch in populations of cochlear-nucleus, Chop-S with different characteristic frequencies, and chopping rates. Thus, populations of cochlear-nucleus Chop-S units, together with their target units presumably located in the inferior colliculus, may serve to establish a stable rate-place code of pitch at the level of the auditory cortex.
从谐波复合音中提取音高信息背后的神经处理本质仍不清楚。在听神经上进行的电生理研究以及许多心理物理学和建模研究表明，通过对听神经纤维的时间发放模式应用类似自相关的机制，可能成功提取音高。当前的建模研究调查了位于哺乳动物腹侧耳蜗核（VCN）中的持续斩波（Chop-S）单元群体在此过程中可能发挥的作用。首先，研究表明计算机模拟可以预测对豚鼠VCN中记录的单个Chop-S单元对周期性和准周期性声音的反应。其次，研究表明周期性或准周期性声音的基频在模拟的Chop-S单元群体的一阶峰峰间隔统计中得到体现。当斩波率等于声音的基频时，在广泛的特征频率范围内都是如此。该模型能够模拟涉及迭代波纹噪声的音高高度和音高强度、音高的主导区域、相位对音高高度和音高强度的影响、非谐波刺激的音高以及正弦调幅噪声的音高的心理物理学研究结果。模拟结果表明，Chop-S单元群体的峰峰间隔统计变化与人类感知的音高变化具有良好的一致性。有人提出，腹侧耳蜗核中的Chop-S单元可能在音高提取中发挥重要作用：它们可以将在听神经中观察到的纯时间音高编码转换为耳蜗核中具有不同特征频率和斩波率的Chop-S单元群体的时间位置音高编码。因此，耳蜗核Chop-S单元群体及其可能位于下丘的目标单元可能有助于在听觉皮层水平建立稳定的音高率-位置编码。
