Evaluating auditory brainstem responses to different chirp stimuli at three levels of stimulation

Auditory brainstem responses (ABRs) are recorded in ten normal-hearing adults (20 ears) in response to a standard 100 micros click and five chirps having different durations (sweeping rates). The chirps are constructed from five versions of a power function model of the cochlear-neural delay that is based on derived-band ABR latencies from N=81 normal-hearing adults [Elberling, C., and Don, M. (2008). J. Acoust. Soc. Am. 124, 3022-3037]. The click and the chirps have identical amplitude spectra and, in general, for each of the three stimulus levels 60, 40, and 20 dB nHL, the ABRs to the chirps are significantly larger than the ABRs to the click. However, the shorter chirps are the most efficient at higher levels of stimulation whereas the longer chirps are the most efficient at lower levels. It is suggested that two different mechanisms are responsible for these observed changes with stimulus level--(1) upward spread of excitation at higher levels, and (2) an increased change of the cochlear-neural delay with frequency at lower levels.