Intensity coding in low-frequency auditory-nerve fibers of the guinea pig

Rate-level functions from 130 auditory-nerve fibers with characteristic frequencies below 3.5 kHz have been recorded. The relationship between rate-level function type and other properties of auditory-nerve fibers was similar to that previously reported for a high-frequency population in the same species [characteristic frequencies greater than 8 kHz-Winter et al., Hear. Res. 45, 191-202 (1990)]. To estimate whether there is sufficient information in the changes in discharge rate from auditory-nerve fibers to account for the intensity discrimination performance observed in humans (for 1-kHz tone bursts), the Sachs-Abbas model was modified to produce the variation in rate-level functions found in guinea pig auditory-nerve fibers. The ability of modeled, single auditory-nerve fibers and populations of these fibers to signal differences in intensity has been calculated. Optimal combination of information from those fibers assumed to synapse beneath just one inner hair cell resulted in a discrimination performance that exceeded human psychophysical performance up to sound levels of 113 dB SL. It is concluded from these results that there is more than sufficient information present in the changes in discharge rate of a localized population of guinea pig auditory-nerve fibers to account for the intensity discrimination performance of humans as measured psychophysically.