The P300 auditory event-related potential: a method to assess bimodal benefit?

Introduction: A growing amount of cochlear implant (CI) users have contralateral residual hearing. These patients often benefit from wearing a contralateral hearing aid (bimodal hearing). Nevertheless, individual performance varies considerably. There is thus a need for measures of bimodal benefit. This study explores whether the cognitive P300 auditory event-related potential (ERP) can be used to assess bimodal benefit. Methods: Cognitive P300 ERPs were recorded using an oddball paradigm with a low-frequency tonal contrast. Subjects were asked to mentally count the amount of deviant stimuli. The accuracy of the stimulus count served as a measure of behavioral performance. Two experiments were conducted. Experiment 1 assessed the P300 ERP paradigm in twelve normal hearing young adults. Based on these results, the P300 ERP paradigm was adjusted as to record P300 in five bimodal listeners. Results: In four out of five bimodal listeners, the P300 ERP improved in bimodal compared to CI-only listening. In these subjects, morphology improved, latencies decreased, and amplitudes increased in the bimodal condition. Interestingly, the subject with the largest improvement in the P300 ERP also showed the largest improvement on the behavioral task. Conclusion: The present study suggests that CI-users generally benefit from wearing a contralateral hearing aid in order to discriminate low-frequency tonal contrasts. The P300 ERP seems to be a promising technique to objectify bimodal benefit.