AJA Papers in Press
Published online June 20, 2012
American Journal of Audiology 2012; doi:10.1044/1059-0889(2012/12-0006)

American Journal of Audiology 2012;21:190.

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Article

Frequency Dependence of Binaural Interaction in the Auditory Brainstem and Middle Latency Responses

Cynthia G. Fowler

Department of Communicative Disorders, University of Wisconsin-Madison

Jennifer H. Horn

Department of Communication Science and Disorders, University of Pittsburgh and Eisenhower Balance Institute, Eisenhower Medical Center, Rancho Mirage, CA

Correspondence should be addressed to: Cynthia G. Fowler, Ph.D., Department of Communicative Disorders, 1975 Willow Drive, University of Wisconsin-Madison, Madison, WI 53705, Phone: 1-608-262-6483, FAX: 1-608-262-6466, E-mail: cgfowler{at}wisc.edu.

Purpose: The primary purpose of this investigation was to determine relative frequency representation of binaural function in the brainstem and cortex of adults. The secondary purpose was to compare adult responses to previously-reported infant responses.

Methods: Simultaneous ABRs and AMLRs were recorded monaurally and binaurally in 20 young women. The binaural (BIN) response was subtracted from the summed monaural waves (L + R) to obtain the binaural interaction components (BIC) from waves V (peak A) and Pa (BIC-Pa). Amplitude ratios were calculated as BIC/L + R. Repeated measure ANOVAs evaluated responses to frequency (500 vs. 4000 Hz), wave condition (L + R vs. BIN), and wave class (ABR vs. AMLR).

Results: Waveforms were present for all conditions. The L + R responses were larger than BIN responses, 500 Hz produced larger amplitudes than 4000 Hz, and Pa was larger than wave V. The largest response overall was the Pa(L + R) response to 500 Hz. For amplitude ratios, BIC-Pa/Pa(L + R)] was larger than Peak A/(V(L + R).

Conclusions: More neural resources are devoted to binaural function in the cortex than in the brainstem, and more resources are devoted to lower frequencies. The adult data confirm that previously recorded infant data reveal binaural immaturity. Longitudinal data should characterize developmental characteristics of binaural function.


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