Assessment of the Velocity of Traveling Waves in the High-Frequency Cochlea of the Dolphin
Short-latency auditory evoked potentials (SLAEP) produced in response to sound impulses with strictly specifi ed 0.5-oct frequency bands, from 11.2–16 to 90–128 kHz, were recorded in bottle-nose dolphins. Using stimuli of constant intensity, SLAEP amplitude depended on the spectral frequency of the stimulus: the higher the frequency, the greater the amplitude. Response shape showed little dependence on spectral band, though the response delay changed with frequency: the higher the frequency, the shorter the delay. The differences in delays between the responses to low-frequency (11.2–16 kHz) and high-frequency (90–128 kHz) stimuli was 0.3 msec. This difference in response delays could be attributed to the propagation time of the traveling wave in the cochlea; the results obtained here were used to calculate the velocity of the traveling wave. These assessments of velocity were from 38.2 oct/msec at the proximal (high-frequency) end of the basilar membrane to 2.8 oct/msec at the distal (low-frequency) end. Comparison of traveling wave velocities in humans and dolphins showed that traveling wave velocity was not linked to the location on the cochlea, but to the characteristic frequency.
Keywordshearing cochlea dolphin traveling wave
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