Visual stimuli can impair auditory processing in cochlear implant users

It has been shown that visual stimulation can activate cortical regions normally devoted to auditory processing in deaf individuals. This neural activity can persist even when audition is restored through the implantation of a cochlear implant, raising the possibility that cross-modal plasticity can be detrimental to auditory performance in cochlear implant users. To determine the influence of visual information on auditory performance after restoration of hearing in deaf individuals, the ability to segregate conflicting auditory and visual information was assessed in fourteen cochlear implant users with varied degree of expertise and an equal number of participants with normal-hearing matched for gender, age and hearing performance. An auditory speech recognition task was administered in the presence of three incongruent visual stimuli (color-shift, random-dot motion and lip movement). For proficient cochlear implant users, auditory performance was equal to that of controls in the three experimental conditions where visual stimuli were presented simultaneously with auditory information. For non-proficient cochlear implant users, performance did not differ from that of matched controls when the auditory stimulus was paired with a visual stimulus that was color-shifted. However, significant differences were observed between the non-proficient cochlear implant users and their matched controls when the accompanying visual stimuli consisted of a moving random-dot pattern or incongruent lip movements. These findings raise several questions with regards to the rehabilitation of cochlear implant users.