Are normal hearing thresholds a sufficient condition for click-evoked otoacoustic emissions?

Transiently evolked otoacoustic emissions (TEOAE) have been reported in several studies as absent in a small minority of normal ears. Other studies have reported TEOAEs in all normal ears. Differences between studies may arise directly from criteria for TEOAE identification, criteria for selection of normals, or statistically due to limited sample sizes. 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 that lacked TEOAEs despite normal hearing threshold levels (HTL). A total of 397 ears from highly cooperative adult subjects were examined under laboratory conditions. Using cross correlation between replicate nonlinear waveforms as the criterion, TEOAEs were present in 99.2% of the sample (lower CI 98.1%). However, careful visual assessment of the recorded waveforms for the remaining ears did not unequivocally show absence of TEOAE characteristics in any ear with normal HTLs. While TEOAE strength varies widely among ears, no clear evidence was found to show that TEOAEs can be absent when HTLs are normal.