ABSTRACT
The auditory system can determine the frequency content of complex tones either by monitoring the spatial distribution of cochlear activity or by examining phase-locked responses of auditory neurons. Psychophysical data suggest that the perceptual apparatus uses both mechanisms. Using harmonic complexes as stimuli, we investigated the ability of cat auditory nerve fibers to encode spectral information in their synchronized responses. Fibers did this extremely well. Resolution of single components greatly exceeded the human ear’s ability to do the same thing. At low intensities fiber response spectra resembled acoustic signal spectra, filtered by the fiber’s tuning curve. Response spectra behaved nonlinearly at high intensities. Specifically, representations of spectral edges and changes in amplitude or phase of single components were enhanced for phase-coherent signals but not for random-phase signals. Most features of responses to harmonic complexes could be explained by considering the effects of hair cells’ compressive input-output functions on waveform temporal fine structure.
