ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP8. Effects of complex-sound phase in the chinchilla auditory nerve.

S. Shyamla Narayan

Guang-Di Chen

Boys Town Natl. Res. Hospital, 555 N. 30th St., Omaha, NE 68131

Responses of populations of single auditory nerve fibers in anesthetized chinchillas to three-component stimuli were studied. The carrier frequency ( f[sub c]) was 2 kHz and the modulating frequencies ( f[sub m]) were 100 and 1000 Hz. The sidebands were -6 dB relative to the center component. The phase of the center component was varied from 0 to 180(degrees) in 45(degrees) steps, which produced changes in modulation depth. Discharge synchrony to f[sub m]=100 Hz decreased with increasing stimulus level for CFs close to f[sub c], as previously shown by other researchers. At 20 dB re:unit threshold, maximum synchrony to 100 Hz was observed for CFs close to f[sub c]. The maxima shifted to higher CFs with increase in stimulus level. Synchrony to f[sub c] decreased with phase shifts up to 90(degrees) and increased for phase shifts between 90(degrees) and 180(degrees). At 20 dB, synchrony to the lower sideband was less than that to the upper sideband when the phase shift was 90(degrees) and 135(degrees). At 40 dB, 0(degrees) and 180(degrees) phase shifts produced higher discharge synchrony to the lower sideband. Also at 40 dB, the phase dependence of the synchrony to the two sidebands differed most at the lower CF regions. The changes in discharge synchrony due to phase changes must reflect cochlear nonlinearities because the amplitude ratios of the stimulus components were held constant. [Work supported by DC00341.]