The smaller the frequency-to-place mismatch the better the hearing outcomes in cochlear implant recipients?

Objective To investigate the effect of frequency-to-place mismatch, i.e. the mismatch between the tonotopic frequency map in the cochlea and the frequency band that is assigned to an electrode contact of a cochlear implant (CI) at the same cochlear location on speech perception outcomes, using postoperative CT images. Study design Retrospective observational single-centre study. Methods Retrospective pre- and postoperative clinical CT data of 39 CI recipients with normal cochlear anatomy were analysed in an otological surgical planning software. The tonotopic frequency at each electrode position was estimated using the Greenwood function. For each patient, frequency-to-place mismatch between the tonotopic frequency and the fitted centre frequency for each electrode contact was calculated. The influence of frequency-to-place mismatch on speech perception in noise at 6 and 12 months after CI activation was studied. Results A significant linear correlation was found between the frequency-to-place mismatch and speech perception in noise 6 months after cochlear implantation (p < 0.05). The smaller the frequency-to-place mismatch, the better the initial speech perception in noise results of the CI recipients. The significant effect disappeared after 12 months CI experience. Conclusion The study findings support the idea of minimizing the frequency-to-place mismatch in CI recipients in order to pursue better initial speech perception in noise. Further research is needed to investigate the prospect of tonotopic fitting strategies based upon postoperative CT images of the exact locations of the electrode contacts.

Automated summary

The study demonstrates that there is a significant linear correlation between frequency-to-place mismatch and speech perception in noise six months after cochlear implantation. Minimizing this mismatch can lead to better initial speech perception outcomes for cochlear implant recipients. However, the effect seems to disappear after twelve months of experience with the cochlear implant. Additional research is needed to explore tonotopic fitting strategies based on postoperative CT images of electrode contact locations.