Normative data bases for electrophysiologic, biomechanical and psychoacoustic measures of human hearing are being developed as instrumentation comes on line. Data has been gathered on otacoustic emissions (OAEs) from normal, healthy subjects with excellent hearing and in certain patient populations for future use. We have been collecting norms in three major categories of OAEs: spontaneous otacoustic emissions (SPOAEs); transiently evoked otacoustic emissions (TEOAEs); and distortion product otacoustic emissions (DPOAEs). We are studying the frequency specificity and amplitude of SPOAEs in healthy adult volunteers to look at intersubject variability. TEOAEs are known to have a highly repeatable frequency dispersion in individual ears. It is known that most individuals with hearing at or better than 25 dB will exhibit TEOAEs measurable with currently available instrumentation. We are studying suppression of TEOAEs, known to be mediated by the superior olivary complex. No data are available in the literature on the percentage of normal human subjects exhibiting suppression, the precise specifications of the auditory stimuli that best elicit suppression, replicability, and the effect of age or gender on suppression. DPOAEs are also being collected using unequal primary auditory signals. The data offer a sensitive indicator of active biomechanical processes in the human cochlea as measured by the delta of emissions amplitudes. It is anticipated that DPOAEs will provide a measure of early cochlear changes due to ototoxicity, noise trauma or other progressive processes.
