Assessing the benefits of anatomy-based fitting method among experienced adult cochlear implant users

Abstract

Cochlear implant (CI) electrode insertion in commercial CI systems does not occupy the whole length of the cochlea turn, leading to frequency-to-place (FPM) mismatch that could affect place pitch percept among CI users. To minimize FPM due to electrode insertion, the anatomy-based fitting (ABF) method has been introduced by one of the CI manufacturers. Hence, this study aims to assess the benefits of the ABF CI programming method among experienced adult CI users compared to the outcomes from the normally used conventional-based fitting (CBF) map. The study employed an experimental prospective study design that used purposive sampling to analyse the outcomes at baseline, three- and six months post-ABF. Pre-ABF, all participants were assessed using their CBF maps. Outcome measures include the following: Consonantvowel- consonant (CVC) scores in quiet and in +5dB signal-to-noise ratio (SNR), frequency discrimination thresholds at 500, 1000, 2000, and 4000 Hz, and subjective ratings. Participants’ quality of life was also measured with their CBF and at six months post-ABF using the Cochlear Implant Quality of Life (CI-QOL) instrument. During the outcome measures, all the stimuli were presented randomly via a loudspeaker positioned at zero degrees azimuth at 30 dB SL in a soundproof audiology room. Participants’ tasks were to repeat the presented phonemes verbally in the speech perception test, indicating present or not the difference in the tones presented in pairs for the frequency discrimination task, and finally listen to a recorded passage and subjectively rate listening comfort, speech understanding, and map preference of the map. Regarding the ABF map, the positions of each intracochlear electrode and their angular insertions were detected by a software called Otoplan using a postoperative computed tomography scan. Otoplan information was imported into the Maestro CI fitting software to generate an ABF map. The magnitude of the ABF’s center frequencies of the frequency allocation table in the speech processors shifted largely concerning their CBF maps, ranging from 619 Hz to 2050 Hz across participants, which indexed the FPM. The baseline assessment for the ABF map was performed after 14 days of ABF fitting, which was provided as a habituation period. The outcomes of speech perception scores for the baseline measurements were consistently higher in the ABF than in the CBF maps (p<0.05) in quiet and noise. Across time, the speech perception scores in quiet and in noise, frequency discrimination abilities for 1kHz, 2kHz, and 4kHz, and the subjective ratings of all three domains showed significantly better ratings in ABF than the CBF maps and between initial and at six months post- ABF (p<0.05). The overall CI-QOL score difference between CBF, and six months of ABF revealed a significant difference (p<0.05). The results suggest that audiologists should consider fitting the ABF map to improve hearing outcomes, especially for speech recognition in noise, at least among experienced adult CI users