Responses of the auditory system to complex tones were summarized.
As in the auditory nerve, tuning curve and nonlinearity of the basilar membrane vibration were found. Isolated outer hair cells were also well tuned. Combination tones can be explained by this nonlinearity which comes from the active process.
Two-tone suppression found in the auditory nerve was also detected in the receptor potential of the inner hair cells. Phase-locked response to complex tones was visublized by period histograms, which was susceptible to the sound pressre level.
“Missing fundamental” is an classical problem of auditory physiology. There are two theories. Temporal theory focuses on the periodic discharge of fibers, and pattdrn theory utilizes the spectral pattern of the complex.
Stimulated by artificial vowels, most fibers saturate at high sound pressure level, but formant pattern is preserved in the ALSR neurogram.
At the cochlear nucleus, neurons which show strong inhibition may extract the feature of the complex. Central beats and binaural masking suggest that phase infomation is carried to some center concerning binaural audition.
Auditory cortical neurons show rather simple feature extraction in contrast to the visual cortex. Whole feature may be represented by the total responses of many cortical neurons.
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