Measuring human cochlear traveling wave delay using distortion product emission phase responses.

A method is presented here in which cochlear traveling wave delays are estimated through the measurement of distortion product emission phase (DPE) responses. This method assumes that the site of generation of DPEs is at the f2 place. Eighteen adult female and 18 adult male human ears, all with normal hearing, underwent DPE testing. For each ear, DPE phase responses were computed for eight values of f2 varying from 10 to 0.78 kHz. Linear DPE phase versus DPE frequency relationships were found. Estimates of traveling wave delay from the ear canal to the f2 place varied from about 1 ms for the 10-kHz place to 3.5 ms for the 0.78-kHz place. These estimates agree well with previous traveling wave delay estimates using electrocochleography. Test-retest comparisons of delay estimates were generally within 0.25 ms. In addition, within-subject interaural delay differences were smaller than between-subject interaural differences. Within-subject interaural delay differences were generally less than 0.5 ms. Male ears, when grouped together, had significantly longer delays (8%) to the 0.78-kHz place in comparison to female ears. The effect of DPE stimulus level on delay is presented for stimulus levels between 15 and 60 dB SPL. These data support the use of DPE phase responses as estimates of cochlear traveling wave delay. In comparison with electrophysiological and psychophysical techniques this method is purely cochlear-based and has the advantage of being rapid and noninvasive.