Acoustic bandwidth effects on envelope following responses to simulated bimodal hearing

Bimodal hearing, which combines a cochlear implant (CI) with a contralateral hearing aid, provides significant speech recognition benefits in quiet and noise. These benefits have also been observed in normal-hearing listeners using vocoder-based CI simulation combined with low-pass filtered speech, even with acoustic bandwidths as narrow as 125–250 Hz. However, it is challenging to measure the optimal acoustic amplification with difficult-to-test populations, such as young children and adults with disabilities. The frequency following response (FFR) offers a potential solution to this problem, as it objectively quantifies subcortical phase-locking to speech features. Recently, FFR fundamental frequency amplitude in the non-implanted ear was found to be well-correlated with bimodal benefit in CI patients. The present study aimed to parametrically examine acoustic bandwidth effects (125, 250, 500, and 750 Hz) on speech evoked FFRs using simulated bimodal stimuli. We hypothesized that FFR_env amplitudes would increase as bandwidth increases up to 750 Hz and the minimal acoustic bandwidth needed to derive FFR bimodal benefit is less than 250 Hz.