Responses of auditory nerve fibers to harmonic and mistuned complex tones.

Responses of auditory nerve fibers were obtained to harmonic complex tones in which single components could be mistuned. Human listeners hear the harmonic tones as single sounds, but the same tones with one component mistuned are heard as two separate sounds. Fourier analysis of the temporal discharge patterns indicated that auditory nerve fibers typically responded to one or two stimulus components near the fibers' characteristic frequencies. At low stimulus levels, the discharge patterns could also exhibit low-frequency modulation that was produced by beating of two higher-frequency components. The same components were observed in the response spectra, whether those components were part of the original harmonic series or had been mistuned. The discharge patterns and response spectra were consistent with expectations based on previous studies of auditory nerve fibers with harmonic tones and other complex sounds. However, the discharge patterns differed dramatically from the discharge patterns elicited from inferior colliculus neurons by comparable stimuli.