Auditory brainstem responses to a chirp stimulus designed from derived-band latencies in normal-hearing subjects.

In an attempt to compensate for the temporal dispersion in the human cochlea, a chirp has previously been designed from estimates of the cochlear delay based on derived-band auditory brain-stem response (ABR) latencies [Elberling et al. (2007). "Auditory steady-state responses to chirp stimuli based on cochlear traveling wave delay," J. Acoust. Soc. Am. 122, 2772-2785]. To evaluate intersubject variability and level effects of such delay estimates, a large dataset is analyzed from 81 normal-hearing adults (fixed click level) and from a subset thereof (different click levels). At a fixed click level, the latency difference between 5700 and 710 Hz ranges from about 2.0 to 5.0 ms, but over a range of 60 dB, the mean relative delay is almost constant. Modeling experiments demonstrate that the derived-band latencies depend on the cochlear filter buildup time and on the unit response waveform. Because these quantities are partly unknown, the relationship between the derived-band latencies and the basilar membrane group delay cannot be specified. A chirp based on the above delay estimates is used to record ABRs in ten normal-hearing adults (20 ears). For levels below 60 dB nHL, the gain in amplitude of chirp-ABRs to click-ABRs approaches 2, and the effectiveness of chirp-ABRs compares favorably to Stacked-ABRs obtained under similar conditions.