The effect of signal processing time synchronization on speech discrimination in noise for bimodal cochlear implant users

Hearing aid amplification and cochlear implant application, which are used in the rehabilitation of hearing loss, increase the auditory and speech perception performance of the user, thanks to the new technologies developed. Studies have shown that bimodal users benefit from the benefits of binaural hearing. These advantages may be different for each individual. One of the reasons for this is explained by the amount of residual hearing present in the non-implanted ear. One of the problems that arise in bimodal use is the delay incompatibility caused by these two different applications. This delay mismatch time can vary between 3 and 11ms. MED-EL cochlear implant technology seeks a solution to the problem caused by signal processing delay incompatibility in hearing aids with the Full Bimodal Synchronization feature used in new processor models. In our study, the effect of Full Bimodal Synchronization mode on speech discrimination in noise was evaluated. In our study, the evaluation was performed with Turkish Matrix Test in cochlear implant, bimodal and Full Bimodal Synchronization mode. When the obtained critical Signal to Noise Ratio (SNR) values are compared; There was a statistically significant difference between bimodal stimulation and use with cochlear implants (p<0.01). These results support the studies in the literature. When the critical SNR values obtained in Bimodal stimulation and Full Bimodal Synchronization mode were compared, no statistically significant difference was found (p=0.204; p>0.05). However, the critical SNR values in the Full Bimodal Synchronization mode were obtained lower than in bimodal stimulation(Critical SNR with cochlear implants: 18.14±12.89, Bimodal critical SNR: 9.49±12.25, Critical SNR in the Full Bimodal Synchronization mode: 6.26±8.45). The scores obtained from the Speech Discrimination test (SD), which was performed in quietness in free field in Full Bimodal Synchronization mode, showed a statistically significant difference compared to the SD scores performed with cochlear implants and bimodal stimulation (p=0.001; p<0.01). It was observed that SD scores increased in the Full Bimodal Synchronization mode. In the same way, there was a statistically significant difference when the SD scores of cochlear implant and bimodal stimulation were compared(p=0.001; p<0.01). The results of the study are that the Full Bimodal Synchronization mode in noise and quietness increases the ability to discriminition speech. However, due to limitations in the study, further research needs to be done. Keywords: Cochlear implant, hearing aid, bimodal stimulation, Full Bimodal Synchronization, kritik Signal Noise Ratio, Turkish matrix test