SIGNAL TO NOISE CONSTRAINTS ON MAXIMUM LENGTH SEQUENCE AUDITORY BRAIN-STEM RESPONSES

In conventional auditory brain stem response (ABR) testing, the stimulus rate must be low enough that the responses do not overlap. By using stimulus patterns derived from the pseudorandom binary series known as maximum length sequences (MLSs), it is possible to stimulate at mean rates of hundreds of clicks per second, and extract the responses. It has been suggested that this could reduce test time appreciably, but there is reason to believe that the MLS ABR is intrinsically noisier than conventional averaging. To test this premise, 10 ears were tested with conventional ABR procedures and with MLS ABRs having 2, 4, and 8 times as many stimuli per second as the conventional condition. Noise levels in control runs were in agreement with predictions. With a 40 dB nHL stimulus, wave V amplitude decreased in the MLS ABRs to the extent that none of the MLS conditions was as efficient as the conventional ABR. Any assessment of the value of MLS ABRs in reducing test time must take into consideration the higher noise levels inherent in this procedure.