Estimating the acoustic reflex threshold from wideband measures of reflectance, admittance, and power

Objective. A method was developed to estimate the contralateral acoustic re flex threshold using shifts in wideband energy reflectance, admittance magn itude and power. Design: In the first experiment contralateral reflex thresholds for a noise activator were estimated on three adult participants using reflectance, ad mittance and power measurements at frequencies from 250 to 8000 Hz. The ref lex threshold was defined using a magnitude and a correlation technique, bo th having the property of examining the pattern of the reflex-induced shift across a fairly broad frequency range (250 to 2000 Hz). In the second expe riment, the magnitude method was modified to include an F test for the comp arison of the magnitude of reflex-induced shifts in reflectance, admittance and power relative to response differences in a no-activator baseline cond ition. Data from four additional participants then were analyzed across a b roader frequency range using a method that combined magnitude and correlati on methods of estimating reflex thresholds. Results. Acoustic reflex thresholds were obtained using reflectance, admitt ance and power-level measures in all subjects in both experiments. Individu al reflex threshold estimates were as much as 24 dB lower than with the cli nical system, with an average of approximately 14 dB lower for the three pa rticipants in the first experiment, and approximately 18 dB lower for the f our participants in the second experiment. Conclusions. Wideband measures of reflectance, admittance and power were su ccessfully used to estimate acoustic reflex thresholds in seven participant s. A reflex threshold test was devised based on the magnitude of the respon se shift in the presence of a contralateral activator, and the similarity o f the response shift spectra across frequency between successive activator levels. Across all participants in the study, the new test yielded a more s ensitive measure of the acoustic reflex threshold than the clinical method. This finding has both clinical and theoretical implications for the study of the acoustic reflex.