Zhao H B, Liang Z A
Shanghai Institute of Physiology, Chinese Academy of Sciences.
Hear Res. 1995 Feb;82(2):244-56. doi: 10.1016/0378-5955(94)00181-o.
The modulation frequency (Fm), particularly high Fm (> 200 Hz), in amplitude modulated (AM) tones can elicit the perception of the periodicity pitch (Langner, 1992). In this study, single unit responses to the Fms of the sinusoidal AM tones were investigated at 50 to 90 dB SPL. The recordings were made from the dorsal cochlear nucleus (DCN) of neuroleptic anesthetized guinea pigs with an intact cerebellum. The DCN units show a good capability of phase-locking to Fm at 400-1200 Hz. On-S-type II and Pauser/Buildup (P/B) units have a high modulation gain (7.2-8.3 dB). P/B units can preserve the high modulation gain (5-9 dB) up to 90 dB SPL. The modulation gain exponentially increases with decreasing modulation depth (Dm) and the phase-locking is detectable even at the Dm as low as 2-5%. The 'central skipping' of the phase-locking peak has been found at deep Dms in a few cases. The synchronization is independent of the discharge rate and can remain high even when the responses to AM tones are inhibited below the spontaneous activity. Such encoding behaviors over the unit's response area show that the Fm phase-locking is strong near or at its characteristic frequency (CF). The synchronization index (SI) versus carrier frequency (Fc) curve is similar to the inverse shape of tuning curve but more narrowly tuned than the iso-intensity function of pure tones at moderate to high intensity levels. The phase-locking is related to the unit's spontaneous rate (SR). The average modulation gain of the lower SR (< or = 2 spikes/s) units is 5 dB higher than that of the higher SR (> 2 spikes/s) units (8.16 and 2.92 dB, respectively) at 70 dB SPL. These results suggest that AM information is temporally encoded over broad ranges of modulation parameters in the DCN and is conveyed by the Fc channel. Such a timing mechanism can play an important role in processing of complex sounds under normal acoustic conditions.
调制频率（Fm），特别是高调制频率（>200Hz）的调幅（AM）音调，能够引发周期性音高的感知（朗纳，1992年）。在本研究中，在50至90dB SPL的声压级下，研究了单个单元对正弦调幅音调的调制频率的反应。记录是在具有完整小脑的抗精神病药物麻醉的豚鼠的背侧耳蜗核（DCN）中进行的。DCN单元在400 - 1200Hz频率下对Fm具有良好的锁相能力。开启型II型和暂停/增强（P/B）单元具有较高的调制增益（7.2 - 8.3dB）。P/B单元在高达90dB SPL的声压级下仍能保持较高的调制增益（5 - 9dB）。调制增益随调制深度（Dm）的减小呈指数增加，即使在低至2 - 5%的Dm时也能检测到锁相。在少数情况下，在较深的Dm时发现了锁相峰值的“中心跳跃”。同步与放电率无关，即使对调幅音调的反应被抑制到低于自发活动水平时，同步仍可保持较高水平。在单元的反应区域内的这种编码行为表明，Fm锁相在其特征频率（CF）附近或处很强。同步指数（SI）与载波频率（Fc）曲线类似于调谐曲线的反形状，但在中高强度水平下比纯音的等强度函数调谐更窄。锁相与单元的自发率（SR）有关。在70dB SPL时，较低自发率（<或=2个脉冲/秒）单元的平均调制增益比高自发率（>2个脉冲/秒）单元高5dB（分别为8.16dB和2.92dB）。这些结果表明，调幅信息在DCN中在广泛的调制参数范围内进行时间编码，并通过Fc通道传递。这种定时机制在正常声学条件下处理复杂声音时可以发挥重要作用。
