IPSILATERAL SUPPRESSION OF TRANSIENT EVOKED OTOACOUSTIC EMISSIONS IN ADULTS

Abstract

Background Measurement of the medial olivocochlear (MOC) reflex provides useful clinical information for understanding the function of the auditory system. Although transient evoked otoacoustic emission (TEOAE) suppression has been demonstrated to be an indicator of MOC activity, its full role and fine details of TEOAE suppression spectra are still not clear. The aim of this study was to investigate details of ipsilateral suppression of TEOAEs in normally hearing adults. Material and Methods Exactly 29 adults (13 males, 16 females, mean age 26.5 years, range 18–42 years), who passed a battery of tests including otoscopy, pure tone audiometry, immittance, and TEOAE tests, participated in the study. Suppression was evaluated by comparing TEOAEs obtained with and without an ipsilateral suppressor in a forward-masking paradigm. Results In general, suppression was small – less than 1.4 dB at all frequencies studied. The spectrum of mean TEOAE suppression showed suppression was greatest between 586 and 3711 Hz (0.6–1.4 dB) but less than 0.6 dB between 3906 and 4883 Hz. Mean suppression increased with post-stimulus time from 0.1 dB in the 2–4 ms time window to a maximum of 2.26 dB in the 16–18 ms window; the mean suppression between 8 and 18 ms after noise stimulation was 1.32 dB (range=0.22–3.23 dB). There were no significant gender or ear-laterality effects. Noise levels as measured in the ear canal were found to have a significant effect on calculated suppression at some frequencies. Conclusions The present study provides evidence of small ipsilateral TEOAE suppression by forward-masking noise in normally hearing adults. However, care is needed in interpreting the findings as noise in the ear canal can be a confounding factor during measurement of TEOAE suppression.