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Z A Liang

Publications and source records attributed to Z A Liang.

5 recordsLinked to original sources
PubMed1997

Temporal encoding and transmitting of amplitude and frequency modulations in dorsal cochlear nucleus.

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.

Acoustic Stimulation↗
PubMed1996

Processing of modulation frequency in the dorsal cochlear nucleus of the guinea pig: sinusoidal frequency-modulated tones.

Frequency- and amplitude-modulated (FM and AM, respectively) tones are important information-bearing elements in voice sounds and can also be produced by the spatial movement of sound sources. Zhao and Liang (1995) recently reported the response features of dorsal cochlear nucleus (DCN) neurons to AM tones. In the present study, the responses of the guinea pig DCN neurons to sinusoidal FM (SFM) tones were examined. Discharges of the DCN units to the SFM tones phase-locked to the stimulus modulation frequencies (fm). The phase-locked discharge patterns existed over broad ranges of modulation parameters and at stimulus levels as high as 95 dB SPL or modulation depths (dm) as low as 2%. Robust phase-locking to the fm was observed in samples of all DCN unit types studied. The means of best fm (Bfm) and upper limit fm (ULfm) of all recorded units were 510 Hz and 940 Hz, respectively. Pauser/Buildup (P/B) units had mean maximum synchronization index (SImax) of 0.57. ON units had the highest Bfm with the mean of 646 Hz and subtype ON-S showed the highest mean of SImax at 0.63. Phase-locking to the fm was independent of discharge rates and existed even when the discharge rates were reduced to the background spontaneous rate (SR). A few units showed stronger synchronous responses to the square and triangular FM stimuli instead of the SFM tones. The relationship between the modulated responses and the unit's response area were further examined. The fm phase-locking occurred to modulation bands (or frequency ranges) within the response area, with the modulation bands as narrow as +/- 160 Hz in the central inhibitory areas of the type IV units. As the width of the modulation band changed within a unit's response area, the phases of the fm phase-locked responses of P/B units linearly changed while for Onset units, the change was lesser. The P/B and Onset units had a pi phase shift and a pi/2 phase change, respectively, as carrier frequencies (fc5) passed through characteristic frequencies (CF) and the excitatory/inhibitory response boundaries. The phase-locked responses to the fms were dependent on the SR but were independent of the CF. Low-SR (< or = 2 spikes/s) units had higher synchronization of responses to the fm than the high-SR (> 2 spikes/s) units (SImax = 0.64 and 0.42 respectively). These results suggest that the temporal characteristics of the fm is effectively represented in the responses of DCN units to the SFM tones. Such temporal encoding behavior can play an important role in the processing of the complex sounds in the auditory system. These results also have implications for a possible role for the DCN is in identifying the spatial movement of a sound source.

Acoustic Stimulation↗
PubMed1995

Processing of modulation frequency in the dorsal cochlear nucleus of the guinea pig: amplitude modulated tones.

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.

Acoustic Stimulation↗