P38 Does reverberation affect the bimodal or audiovisual speech intelligibility benefit in cochlear implant users?
Cochlear implant (CI) users with access to contralateral acoustic hearing show better speech intelligibility in noise when using both ears simultaneously (bimodal benefit). Moreover, intelligibility is typically better when listeners have visual access to simultaneous articulatory movements of the speaker (audiovisual benefit). This study investigated the effect of reverberation on the amount of either bimodal or audiovisual speech intelligibility benefit. Therefore, seven CI listeners (five bimodal, two single-side deaf) and six normal-hearing listeners (as controls) were tested with the German HSM sentence test in noise at individually fixed signal-to-noise ratios using stationary noise with long-term speech spectrum. Speech stimuli were presented via loudspeaker either dry or reverberant, i.e., convolved with a room-impulse response with reverberation time of 1 ms. In addition to the acoustic stimuli, simultaneous visual stimuli were presented over a flatscreen monitor in half of the conditions. CI users listened to the stimuli in three different modalities: acoustic-only, electric-only and bimodal. Preliminary results showed significant average audiovisual benefits of 13.4% in CI users and 13.6% in normal-hearing listeners. Bimodal benefit in CI users was 31.6% with respect to electric-only listening, and 31.5% with respect to acoustic-only listening. In comparison to reverberant speech, non-reverberant speech was on average 26.9% better intelligible for CI listeners. Significant interactions between the factors reverberation and visual cues (p = 0.017), but not between reverberation and modality (p = 0.892) were found, indicating that audiovisual benefit was larger with dry speech, in particular with electric-only listening. In addition, this study found that bimodal benefit was governed by better-ear-listening in dry conditions. In contrast, speech intelligibility was significantly higher in bimodal conditions than in the better ear in the reverberant condition, indicating a combined benefit.