Visual benefit in bimodal training with highly distorted speech sound

Artificial auditory devices such as cochlear implants (CIs) and auditory brainstem implants (ABIs) have become standard means to manage profound sensorineural hearing loss. However, because of their structural limitations compared to the cochlea and the cochlear nucleus, the generated auditory sensations are still imperfect. Recipients need postoperative auditory rehabilitation. To improve these rehabilitation programs, this study evaluated the effects of bimodal (audio–visual) training under seven experimental conditions of distorted speech sound, named noise-vocoded speech sound (NVSS), which is similarly processed with a speech processor of CI/ABI. Word intelligibilities under the seven conditions of two-band noise-vocoded speech were measured for auditory (A), visual (V) and auditory–visual (AV) modalities after a few hours of bimodal (AV) training. The experiment was performed with 56 subjects with normal hearing. Performance of A and AV word recognition was significantly different under the seven auditory conditions. The V word intelligibility was not influenced by the condition of combined auditory cues. However, V word intelligibility was correlated with AV word recognition under all frequency conditions. Correlation between A and AV word intelligibilities was ambiguous. These findings suggest the importance of visual cues in AV speech perception under extremely degraded auditory conditions, and underscore the importance of the possible effectiveness of bimodal audio–visual training in postoperative rehabilitation for patients with postlingual deafness who have undergone artificial auditory device implantation.