Frequency dependence of interear asymmetries and binaural interaction in the human ABR

In the present study derived auditory brain stem responses utilizing high pass masking were used to determine the frequency dependence of interear asymmetries and binaural interaction. Eight female adults with normal hearing participated in this study. The ABR was recorded for right and left ears and binaurally with clicks alone and in the presence of high pass masking noise with the following cutoff frequencies: 4000, 2000, 1000, and 500 Hz. Derived responses were obtained by successive waveform subtractions and were analyzed for significant right/left asymmetries, for latency and amplitude, utilizing a statistical method discussed by Spivak (unpublished doctoral dissertation, City University of New York, 1985). The binomial test revealed that the frequency of latency and amplitude asymmetries was not significantly above chance levels for the unmasked measures or for any of the derived bandwidth measures. The binaural interaction component (BIC) was obtained utilizing the method proposed by Dobie and Berlin (Arch Otolaryngol 1979; 105:391-398), and was expressed as a percentage of the true binaural. Analysis of variance revealed no significant differences in the ratio of the BIC amplitude to the true binaural amplitude as a function of the high pass masking cutoff frequency. The present data suggests that for the frequency bandwidths analyzed in this study, there are no specific frequency dependencies of interear asymmetries or binaural interaction in the human ABR.