Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, USA.
Department of Biomedical Engineering, Boston University, Boston, MA, USA.
J Assoc Res Otolaryngol. 2021 Jun;22(3):319-347. doi: 10.1007/s10162-021-00792-5. Epub 2021 Apr 23.
Although pitch is closely related to temporal periodicity, stimuli with a degree of temporal irregularity can evoke a pitch sensation in human listeners. However, the neural mechanisms underlying pitch perception for irregular sounds are poorly understood. Here, we recorded responses of single units in the inferior colliculus (IC) of normal hearing (NH) rabbits to acoustic pulse trains with different amounts of random jitter in the inter-pulse intervals and compared with responses to electric pulse trains delivered through a cochlear implant (CI) in a different group of rabbits. In both NH and CI animals, many IC neurons demonstrated tuning of firing rate to the average pulse rate (APR) that was robust against temporal jitter, although jitter tended to increase the firing rates for APRs ≥ 1280 Hz. Strength and limiting frequency of spike synchronization to stimulus pulses were also comparable between periodic and irregular pulse trains, although there was a slight increase in synchronization at high APRs with CI stimulation. There were clear differences between CI and NH animals in both the range of APRs over which firing rate tuning was observed and the prevalence of synchronized responses. These results suggest that the pitches of regular and irregular pulse trains are coded differently by IC neurons depending on the APR, the degree of irregularity, and the mode of stimulation. In particular, the temporal pitch produced by periodic pulse trains lacking spectral cues may be based on a rate code rather than a temporal code at higher APRs.
虽然音高与时间周期性密切相关，但具有一定时间不规则性的刺激可以在人类听众中引起音高感觉。然而，对于不规则声音的音高感知的神经机制还了解甚少。在这里，我们记录了正常听力（NH）兔子下丘脑中单个单位对脉冲串中不同程度的脉冲间隔随机抖动的反应，并与通过另一个组的兔子中的耳蜗植入物（CI）传递的电脉冲串的反应进行了比较。在 NH 和 CI 动物中，许多 IC 神经元对平均脉冲率（APR）的发射率表现出调谐，对时间抖动具有很强的稳定性，尽管抖动往往会增加 APR≥1280Hz 的发射率。刺激脉冲之间的尖峰同步的强度和限制频率在周期性和不规则脉冲串之间也是可比的，尽管在 CI 刺激时，高 APR 时的同步略有增加。在 CI 和 NH 动物之间，在观察到的发射率调谐的 APR 范围以及同步反应的出现率方面都存在明显的差异。这些结果表明，IC 神经元根据 APR、不规则性程度和刺激模式，对规则和不规则脉冲串的音高进行不同的编码。特别是，缺乏频谱线索的周期性脉冲串产生的时间音高可能基于速率码而不是较高 APR 时的时间码。
