Derived band auditory brain-stem response estimates of traveling wave velocity in humans. I: Normal-hearing subjects

Estimates of cochlear traveling wave velocity (TWV) were computed from derived band auditory brain-stem response (ABR) latencies in 24 normal-hearing subjects. Wave V latencies were determined for each of six derived frequency bands (unmasked-8 kHz, 8-4 kHz, 4-2 kHz, 2-1 kHz, 1 kHz-500 Hz, and 500-250 Hz). Representative frequencies were assigned to the derived bands by estimating their energy midpoints, and cochlear positions corresponding to these frequencies were determined using Greenwood's [J. Acoust. Soc. Am. 33, 1344-1356 (1961)] place-frequency function for humans. Two procedures were used to estimate TWV. In one procedure, an exponential function of the form l = A + BeCd was fitted to each subject's latency-by-distance data using a least-squares algorithm, and a TWV function was generated by taking the inverse derivative of the latency function with respect to time. In the second procedure, average TWVs between adjacent derived bands were computed directly from subjects' ipsilateral wave V latencies. Values obtained with the two procedures were similar for middle and apical cochlear loci; however, TWV functions produced lower estimates of TWV at the most basal of five cochlear sites. TWVs based on ipsilateral wave V latencies ranged from 5.6 to 78.0 m/s (geometric mean 11.2 m/s) in the cochlear base (7.53 mm from the stapes) and from 1.2 to 3.4 m/s (geometric mean 1.96 m/s) in the cochlear apex (24.1 mm from the stapes). Intersubject variability was large at the most basal point of TWV estimation but was progressively smaller at more apical sites. Mean TWV estimates were lower than those reported by several previous investigators. The range of values obtained in various studies may stem from differences in the procedures used to estimate TWV.