Comparison of transient evoked otoacoustic emission thresholds recorded conventionally and using maximum length sequences

Presenting clicks according to maximum length sequences (MLSs) enables tran sient evoked otoacoustic emissions (TEOAEs) to be recorded at very high sti mulation rates. Despite a decrease in TEOAE amplitude, the very large numbe r of responses obtainable at high rates means that both signal to noise rat io (SNR) and detection sensitivity increase as the click rate increases. Th is study characterises conventional and MLS TEOAEs near threshold for a gro up of normally hearing adults. Stimulus presentation rates of 40 clicks/s ( conventional) and 5000 clicks/s (MLS) were used. Compared to conventional r ecordings, the MLS technique enabled smaller responses to be detected, when averaged for the same time and to the same SNR. TEOAE amplitude recorded a t detection threshold for MLS responses was 13 dB lower than that recorded conventionally. For each individual, MLS recording also produced clear, rep eatable responses at stimulus levels below the detection threshold for conv entional TEOAEs. The click level at TEOAE threshold was 12 dB lower for MLS compared to conventional emissions. These results suggest that TEOAE thres holds are not absolute but strongly related to the detection sensitivity of the recording system and physiological noise. The initial growth rates and the shape of input/output functions were found to be similar for the two r ecording techniques. (C) 2001 Elsevier Science B.V. All rights reserved.