Abstract:
Phase locking of auditory-nerve fibers to the vowel /(epsilon)/ was studied in normal cats and in cats with a noise-induced hearing loss. In normal cats, phase locking to the formant-frequency components of the vowel dominates responses among fibers with BFs near the formant frequencies. At moderate stimulus levels (50--70 dB), in fact, the responses of such fibers are captured by the formant, in that the fibers respond only to the formant frequency. This synchrony capture is not observed in noise-damaged animals. It is reported here that it is also not observed in normal fibers at high sound levels (near 90 dB). Synchrony capture is a nonlinear phenomenon in that it reflects suppression of response to stimulus components within the tuning curve by the strongest component, at the formant frequency. Using simple cochlear models, the conditions necessary for synchrony capture with a vowel stimulus will be demonstrated and related to the changes occurring in deafened animals and at high sound levels. [Work supported by NIH Grant No. DC00109.]