COAE THRESHOLDS .1. EFFECTS OF EQUAL-AMPLITUDE VERSUS SUBTRACTION METHODS

Although research has demonstrated that click-evoked otoacoustic emiss ions (COAEs) elicited by high-level stimuli are useful for identifying hearing loss, the ability of COAEs to predict behavioral thresholds h as not been adequately tested. Results of studies comparing COAE thres holds and behavioral thresholds have been equivocal, perhaps due to th e need for a more rigorous approach to COAE threshold estimation. The present study was designed to address several methodological concerns in COAE threshold testing, particularly the effects of two methods of stimulus presentation on COAE testing and threshold calculation. In on attempt to make COAE threshold estimation consistent across participa nts, COAE threshold calculations were based on mean noise floor levels across participants. COAE and noise floor levels were measured in 15 participants using both equal-amplitude clicks and a subtraction metho d. Broadband COAEs were analyzed into 1/3 octave bands, so that input/ output functions could be examined and COAE thresholds could be calcul ated for each 1/3 octave band. Comparison of the two stimulus methods indicated several differences. Mean noise floor levels for the equal-a mplitude method were approximately 6 dB lower than those measured For the subtraction method across frequency. In many cases COAEs evoked us ing the equal-amplitude method were higher in amplitude than those evo ked using the subtraction method. COAE thresholds measured using the e qual-amplitude click stimuli were significantly lower than those measu red using the subtraction method. The significantly higher thresholds obtained using the subtraction method may be attributed in part to the reduction of COAE amplitude by the subtraction procedure, and not mer ely to the higher noise level. Slopes of the input/output functions we re not significantly different between the two stimulus methods. These results suggest that the equal-amplitude method is preferable for COA E threshold resting because lower noise floor and larger amplitude COA Es may be obtained in the same test time.