DETECTION OF THE BINAURAL INTERACTION COMPONENT IN THE AUDITORY BRAIN-STEM RESPONSE

In humans, the binaural interaction at the brainstem level has been st udied for over 15 years. The binaural interaction component (BIG) is o btained by subtracting the summed auditory brainstem response (ABR) in the monaural stimulus mode from the ABR obtained in the binaural stim ulus mode. By nature of this subtraction process, the signal-to-noise ratio of the difference waveform is poor, requiring an objective detec tion criterion to decide whether a significant BIC is present. In this study, the effectiveness of two analysis methods was compared. The fi rst method is the '3 SD' method, which is based on a signal-to-noise e valuation. The second method is a template matching method, in which t emplates are derived from normal hearing subjects' responses and indiv idual responses are cross-correlated with these templates. The templat es were allowed to shift over a range of -0.8 to 0.8 ms in search of t he maximum correlation coefficient. Thirty-nine subjects with normal h earing and five patients with a unilateral profound hearing loss parti cipated in the study. ABRs were obtained with rarefaction and condensa tion clicks at a rate of 15/s and a level of 70 dB nHL. Latencies of t he ABR waves I, III and V for all normal hearing subjects and for the normal ear of the patients were within the normal range. The efficienc ies of both methods, defined as the number of normal hearing adults wi th a significant BIC plus the number of patients without a significant BIC divided by the total number of subjects, were determined. The res ults show that the '3 SD' method is superior to the template matching method; the efficiencies were 95% and 70% respectively, when responses to rarefaction and condensation clicks were taken together. With the '3 SD' method, a significant BIC is demonstrated in almost all normal hearing subjects (97%). However, the '3 SD' method also falsely indica ted a significant BIC in one patient. These results suggest that the B IC may have clinical value in studying binaural interaction in humans.