Sayles Mark, Winter Ian M
Centre for the Neural Basis of Hearing, The Physiological Laboratory, Cambridge CB23EG, United Kingdom.
J Neurosci. 2008 Nov 12;28(46):11925-38. doi: 10.1523/JNEUROSCI.3137-08.2008.
Neural coding of the pitch of complex sounds is vital for animals' ability to communicate and to perceptually organize natural acoustic scenes. Harmonic complex sounds typically have a well defined pitch corresponding to their fundamental frequency, whereas inharmonic sounds can exhibit pitch ambiguity: their pitch can have more than one value. Iterated rippled noise (IRN), a common "pitch stimulus," is generated from broadband noise by a cascade of delay-and-add steps, with the delayed noise phase-shifted by varphi degrees. By varying varphi, the (in)harmonicity, and therefore the pitch ambiguity, of IRN can be manipulated. Recordings were made from single-units in the ventral cochlear nucleus of anesthetized guinea pigs in response to IRN and complex tones, systematically varying the inharmonicity. In their all-order interspike interval distributions, primary-like and chopper units tuned within the phase-locking range of best frequencies represent the waveform temporal fine structure (which varies with varphi). In contrast, those units tuned to higher frequencies represent the temporal-envelope modulation (independent of varphi). We show a temporal representation of ambiguous pitch for IRN and complex tones based on responses to the stimulus fine structure. Within the dominance region for pitch this representation follows the predictions of classic human behavioral experiments and provides a unifying contribution to possible neuro-temporal explanations for the pitch shift and pitch ambiguity associated with many inharmonic sounds.
复杂声音音高的神经编码对于动物的交流能力以及感知组织自然声学场景的能力至关重要。谐波复合声音通常具有与其基频相对应的明确定义的音高，而非谐波声音可能表现出音高模糊性：它们的音高可以有多个值。迭代波纹噪声（IRN）是一种常见的“音高刺激”，由宽带噪声通过一系列延迟相加步骤生成，延迟的噪声相移了φ度。通过改变φ，可以控制IRN的（非）谐波性，从而控制音高模糊性。在麻醉的豚鼠的腹侧耳蜗核中记录单个神经元对IRN和复合音调的反应，系统地改变其非谐波性。在它们的全阶峰峰间隔分布中，在最佳频率的锁相范围内调谐的初级样和切碎器单元代表波形的时间精细结构（随φ变化）。相比之下，那些调谐到更高频率的单元代表时间包络调制（与φ无关）。我们基于对刺激精细结构的反应，展示了IRN和复合音调的模糊音高的时间表征。在音高的主导区域内，这种表征遵循经典人类行为实验的预测，并为与许多非谐波声音相关的音高偏移和音高模糊性的可能神经时间解释提供了统一的贡献。
