Zhao H B, Liang Z A
Shanghai Institute of Physiology, Chinese Academy of Sciences, People's Republic of China.
Hear Res. 1997 Apr;106(1-2):83-94. doi: 10.1016/s0378-5955(97)00004-x.
Amplitude- and frequency-modulated (AM and FM, respectively) tones have been considered as simplified models of natural sounds. The responses of auditory neurons can phase-lock to the modulation frequency (fm). The encoding and transmitting of such modulation phase-locking are interesting since there is no any fm physical peak in spectrum. In the present study, we approached these issues by recording the phase-locked responses of the dorsal cochlear nucleus (DCN) units in guinea pigs to different AM and FM tones. For AM noise tones without the spectral cues of fm, the unit's discharges still phase-locked to the envelope cycles, but it was generally weaker than to sinusoidal AM (SAM) tones. At 50% modulation depth (dm), the mean modulation gains of Pauser/ Buildup (P/B) units (n = 7) to AM noise tones was -0.61 dB whereas they had a 6.48 dB mean to SAM tones. Similar to the case of AM tones, phase-locking to sinusoidal FM (SFM) tones represented the time courses of frequency changes, and it could be separated and changeable corresponding to the frequency increasing and decreasing. There were differences between the phase-locking to SAM and SFM tones in an identical unit. Both ON and type I/III units tended to have stronger phase-locking to the SFM tones than to the SAM tones. The phase-locking to the possible demodulated fm components was further examined with different carrier frequencies (fc) and pure tones. The DCN units showed poor or no responses to modulation tones out of their response areas even in the low characteristic frequency (CF) units, but the low-CF units had clear phase-locking to pure tones at the similar fm ranges. The puretone phase-locking had a band-pass shape different from the low-pass shape of the auditory nerve fibers. These data suggest that the modulation phase-locking in the DCN units may be based on the temporal modulation cues and transmitted in the carrier place. The temporal integration of modulation information over the unit's response area as an across-frequency temporal processing model was discussed for modulation enhancement in the CN units.
调幅和调频（分别为AM和FM）音调被视为自然声音的简化模型。听觉神经元的反应可以与调制频率（fm）锁相。由于频谱中不存在任何fm物理峰值，这种调制锁相的编码和传输很有意思。在本研究中，我们通过记录豚鼠背侧耳蜗核（DCN）单元对不同AM和FM音调的锁相反应来探讨这些问题。对于没有fm频谱线索的AM噪声音调，单元的放电仍与包络周期锁相，但通常比与正弦调幅（SAM）音调的锁相弱。在50%调制深度（dm）时，暂停/增强（P/B）单元（n = 7）对AM噪声音调的平均调制增益为-0.61 dB，而它们对SAM音调的平均增益为6.48 dB。与AM音调的情况类似，与正弦调频（SFM）音调的锁相代表了频率变化的时间进程，并且它可以随着频率的增加和减少而分离和变化。同一单元中与SAM和SFM音调的锁相存在差异。ON单元和I/III型单元对SFM音调的锁相往往比对SAM音调更强。我们用不同的载波频率（fc）和纯音进一步研究了对可能解调的fm成分的锁相。即使在低特征频率（CF）单元中，DCN单元对其反应区域之外的调制音调也表现出较差的反应或无反应，但低CF单元在相似的fm范围内对纯音有明显的锁相。纯音锁相具有不同于听神经纤维低通形状的带通形状。这些数据表明，DCN单元中的调制锁相可能基于时间调制线索，并在载波位置进行传输。讨论了作为跨频率时间处理模型的单元反应区域上调制信息的时间整合，以增强CN单元中的调制。
