Comparison of cochlear delay estimates using otoacoustic emissions and auditory brainstem responses

Different attempts have been made to directly measure frequency specific basilar membrane (BM) delays in animals, e.g., laser velocimetry of BM vibrations and auditory nerve fiber recordings. The present study uses otoacoustic emissions (OAEs) and auditory brainstem responses (ABRs) to estimate BM delay non-invasively in normal-hearing humans. Tone bursts at nine frequencies from 0.5 to 8 kHz served as stimuli, with care taken to quantify possible bias due to the use of tone bursts with different rise times. BM delays are estimated from the ABR latency estimates by subtracting the neural and synaptic delays. This allows a comparison between individual OAE and BM delays over a large frequency range in the same subjects, and offers support to the theory that OAEs are reflected from a tonotopic place and carried back to the cochlear base via a reverse traveling wave.