ARE NORMAL-HEARING THRESHOLDS A SUFFICIENT CONDITION FOR CLICK-EVOKEDOTOACOUSTIC EMISSIONS

Transiently evoked otoacoustic emissions (TEOAE) have been reported in several studies as absent in a small minority of normal ears. Other s tudies have reported TEOAES in all normal ears. Differences between st udies may arise directly from criteria for TEOAE identification, crite ria for selection of normals, or statistically due to limited sample s izes. In order to understand and model cochlear processes involved in TEOAE generation, it needs to be known whether the presence of normal hearing leads automatically to generation of TEOAEs. The present study set out to establish in a large sample if any ears could be found tha t lacked TEOAEs despite normal hearing threshold levels (HTL). A total of 397 ears from highly cooperative adult subjects were examined unde r laboratory conditions. Using cross correlation between replicate non linear waveforms as the criterion, TEOAEs were present in 99.2% of the sample (lower CI 98.1%). However, careful visual assessment of the re corded waveforms for the remaining ears did not unequivocally show abs ence of TEOAE characteristics in ally ear with normal HTLs. While TEOA E strength varies widely among ears, no clear evidence was found to sh ow that TEOAEs can be absent when HTLs are normal. (C) 1997 Acoustical Society of America.