The feasibility of maximum length sequences to reduce acquisition time of the middle latency response

Maximum length sequences (MLS) have been used to improve the signal-to-nois e: ratio (SNR) of otoacoustic emissions [Thornton, J. Acoust. Sec. Am. 94, 132-136 (1993)] and the auditory brainstem response [Thornton and Slaven, B r. J. Audiol. 27, 205-210 (1993)]. By implication, a shorter recording time would be required to give equal signal-to-noise ratio (SNR). This study ai med to establish whether it is also possible to improve the SNR of the audi tory-evoked potential termed the middle latency response (MLR) using maximu m length sequences (MLS). Recordings of 180 s each were made using a conven tional recording rate and MILS rates of 42, 89, and 185 clicks/s. Three dif ferent stimulus intensities were used in the range 30 to 70 dB nHL. The rat e of 89 clicks/s was found to produce most improvement in SNR for both the N-a-P-a region of the MLR and the N-a-P-b region. This improvement in SNR u sing MLS implies that an MLS rate of 89 clicks/s would produce a fourfold r eduction in recording time for equal SNR over conventional recording for th e P-a-N-b region of the MLR at a stimulus intensity of 70 dB nHL. The laten cy of the Nb wave was found to reduce significantly using MLS. An MLR could not be recorded from every subject in this study, but more subjects had an identifiable response For MLS than for conventional recordings. Use of MLS to record the MLR appears to offer the potential for reduction in test tim e and better wave identification. (C) 2001 Acoustical Society of America.