Effects of click rate on bottlenose dolphin auditory brainstem response signal-to-noise ratio

Abstract

Maximum Length Sequence (MLS) and Iterative Randomized Stimulation and Averaging (I-RSA) methods allow auditory brainstem response (ABR) measurements at high stimulus rates; however, it is not clear if high rates allow ABRs of a given signal-to-noise ratio (SNR) to be measured in less time than conventional averaging at lower rates. In the present study, ABR SNR was examined in six bottlenose dolphins using conventional averaging at rates of 25 and 100 Hz and the MLS/I-RSA approaches from 100 to 1250 Hz. Residual noise in the averaged ABR was estimated using root-mean-square values of the: waveform amplitude following the ABR, waveform amplitude after subtracting two subaverage ABRs, and amplitude variance at a single time point. For all approaches, residual noise decreased with the increasing measurement time. For a fixed recording time, SNR was highest at rates near 500 Hz, but optimal SNRs were only a few dB higher than that for conventional averaging at 100 Hz. Nonetheless, small improvements in SNR could result in significant time savings in reaching criterion SNR. The time savings allowed by the MLS and I-RSA methods will be discussed for both mean and individual data. [Work supported by U.S. Navy Living Marine Resources Program.]