Estimating human cochlear traveling wave velocity using distortion product otoacoustic emission and auditory brainstem response measurements

Estimates of human cochlear traveling wave velocity (TWV) were computed from distortion product otoacoustic emissions (DPOAEs) and tone burst evoked auditory brainstem responses (ABR) obtained with ipsilateral notched-noise masking. All distortion product otoacoustic emission data and auditory brainstem responses were obtained across seven frequencies (.75 to 6 kHz) for four intensity conditions. Traveling wave velocity estimates, as well as absolute DPOAE and ABR latencies, across frequency and intensity were examined. Fifteen normal hearing subjects participated.; Latency and traveling wave velocity estimates from auditory brainstem responses were obtained with tone burst stimulation with and without ipsilateral notched-noise masking. Distortion product otoacoustic emission latency measures and traveling wave velocity estimates were obtained with the “Narrow Frequency Range Phase Gradient Method (O'Mahoney, 1993)” utilizing an f2 sweep paradigm, with f1 remaining fixed. DPOAE latency values were obtained as the phase-lag related to the frequency shift after phase unwrapping. The DPOAE latency calculated was equal to the slope of the “best line” joining the four phase points, utilizing the least squares fit method.; Traveling wave velocity estimates were derived from latency measurements across intensity conditions. Cochlear distance, or cochlear position, was determined using Greenwood's (1961) place map function for humans. A regression was conducted on individual subject traveling wave velocity data in order to fit the data to an exponential function of the form y = A + Bxe −3 + Cx2e−7.; For all subjects, auditory brainstem response and distortion product otoacoustic emission latency measurements were inversely related to intensity and frequency. Auditory brainstem response and distortion product emission latency measurements were found to be relatively equivalent at lower intensity levels. Latency was found to increase as distance from the stapes increased, while traveling wave velocity was found to be inversely related to cochlear distance.; Traveling wave velocity estimates obtained from both auditory brainstem responses and distortion product emissions latency measures were found to have similar intensity-frequency functions. Both velocity estimates demonstrated a linear relationship to frequency at lower intensity levels which became progressively curvilinear as intensity increased.; These findings suggest that distortion product otoacoustic emission measurements provide a rapid, non-invasive, reliable estimate of cochlear travel time and traveling wave velocity. Similarities between the intensity-frequency functions derived from auditory brainstem and distortion product otoacoustic emission traveling wave velocity estimates suggest that a common underlying cochlear mechanism is responsible for these intensity-dependent changes.