Binaural advantages of bimodal stimulation of cochlear implant users

Demiröz B. G., The Benefits of Binaural Hearing Provided by Bimodal Stimulation in Cochlear Implant Users, Hacettepe Üniversitesi Sağlık Bilimleri Enstitüsü Odyoloji Programı Doktora Tezi, Ankara, 2024. This study aimed to explore fundamental frequency (F0) and vocal-tract length (VTL) voice cue discrimination thresholds and performance scores of speech perception in single talker background noise among cochlear implanted (CI, N=23), Bimodal (N=18), and normal hearing (NH, N=29) participants aged 10-30 years. Additionally, a subgroup of bimodal participants (N=11) was retested to acoustic input benefits via hearing aids. Participants were tested with two specifically developed experiments for voice cue discrimination and speech perception, focusing specifically on F0 and VTL cues. Results revealed that, CI and bimodal children had lower sensitivity F0 and VTL discrimination thresholds compared to normal hearing peers, but performed better than postlingual CI adults. CI and Bimodal children performed better in speech perception tests, primarily benefiting from increasing TMR and voice cue differences. The CI and Bimodal children whose F0 thresholds overlapped with NH children were observed to have been implanted early. Test-retest analysis in Bimodal participants showed no significant effect of hearing condition on F0 and VTL sensitivity, hovewer, increasing TMR and using hearing aids (HAs) in the contralateral ear improved accuracy scores in some participants. In conclusion, although CI and Bimodal participants had lower voice cue discrimination thresholds compared to NH peers, they utilized degraded F0 cues to some extent for perception despite spectrotemporal challenges, while VTL cues were more challenging. Moreover, acoustic input via HAs had a benefit on speech perception in some participants. Further exploration of individual visual inspection and demographic details may offer deeper insights into influencing factors on individual variations and performance. Keywords: Voice cue perception, Speech perception, cochlear implant, hearing aid, Bimodal hearing