The binaural interaction component: a method to monitor plasticity in bimodal listeners?

Objectives: To investigate plasticity in the binaural auditory system in bimodal listeners. Background: Bimodal hearing refers to the condition in which electric hearing via a cochlear implant (CI) is combined with residual hearing in the non-implanted ear. Psychoacoustic research suggests that bimodal listeners can benefit from binaural integration. There is, however, an unexplained variability in bimodal outcome. It is hypothesized that at least some of this variability can be explained by plasticity. It is expected that binaural interaction develops with increasing bimodal experience. Furthermore, subjects who wore bilateral hearing aids may be more likely to binaurally integrate electric and acoustic signals. We believe that the binaural interaction component derived from the auditory brainstem response (ABR-BIC) can be a useful technique to measure plastic changes during the first months of bimodal hearing. Methods: ABR-BICs are computed by subtracting the binaural response from the sum of the left and right monaural responses. A protocol that combines acoustic and electric stimulation is set up to obtain ABR-BICs in bimodal listeners. In a first study, ABR-BICs are measured by accounting for the latency differences between the acoustic and the electric wave V. In a second study, ABR-BICs are measured without accounting for this. Results: Both protocols will be presented, as well as the results of a pilot study. Preliminary data of the first study suggests that binaural interaction can occur in bimodal listeners. Conclusions: A better understanding of the mechanisms of inter-subject variability in binaural interaction can lead to better and more adequate counseling