Effect of otoacoustic emissions on just-noticeable differences for intensity in normally hearing subjects.

Measurements of spontaneous and click-evoked otoacoustic emissions (OAEs) were used to classify listeners with normal hearing into one of two categories--those with spontaneous emissions (SOAEs) and high-level transiently evoked emissions (TEOAEs) in both ears (strong emissions) and those with no SOAEs and low-level TEOAEs in either ear (weak emissions). Just-noticeable differences (jnd's) in intensity for 1-kHz pure tones presented at either 60, 40, or 20 dB SL were determined for these two groups using a continuous pedestal technique. Mean jnd's for intensity for the two groups did not differ significantly. Intratest variability was compared and the group with strong emissions had significantly higher variability for presentation levels of 20 dB SL and lower variability at 60 dB SL. Additional testing of intensity jnd's was performed in individuals with strong emissions using pure tones 30 Hz lower than a targeted SOAE frequency. Large interindividual differences were present without a specific pattern. It is concluded that OAE activity level does not affect the mean jnd for intensity discrimination. Individuals with strong emissions have less variance when performing the test at higher levels and more variance for lower level stimuli than do individuals with weak emission characteristics. Because an ear's OAE characteristics can alter performance on psychoacoustic tasks, knowledge of such characteristics is desirable when psychoacoustic results are acquired and reported.