The importance of sound quality in cochlear implants (CIs) has gained significant attention in recent years. While many CI users achieve near-normal speech recognition in quiet conditions, they frequently report poor sound quality. Although the impact of CI technology on sound quality degradation is well-documented, less is known about the contribution of specific “frequency-to-place factors” such as the frequency-to-place mismatch (FTPM) and electrode-neuron interface (ENI). Our study aims to develop innovative testing methods to examine the relationship between sound quality and these individual frequency-to-place factors.

The first method involves frequency manipulation of different vowels: /ɜː/, /a:/, /u:/, and /i:/. Two types of manipulations were performed: in the first, the modification was restricted to the first formant, while in the second, it was applied to the entire vowel. Participants evaluated these shift configurations in terms of “overall preference” and recognition through paired comparisons using a preference rating scale. A Bradley-Terry-Luce model was used to determine the final ranking of the shifting configurations. These methods aim to reveal levels of adaptation to FTPM and ENI quality.

To further separate the effects of these factors, the second method assesses the quality of sound transmission across individual electrodes. This test uses a sound quality experiment based on chord comparisons. Participants were presented with pairs of chords and asked to rate the sound quality, comparing each chord with its inversion. Chord inversions varied by one note within the same harmonic framework, maintaining similar overall quality. These paired comparisons, conducted with various chord triads and their inversions, allow us to evaluate how individual electrodes may degrade sound quality in complex stimuli.

We tested 10 post-lingually deafened adult CI users with over 12 months of listening experience. Preliminary findings indicate good test-retest reliability for all three methods. Results from the vowel experiments show that some participants preferred a shifted configuration to enhance sound quality, though no clear link emerged between vowel and chord preference results. The chord comparisons revealed substantial differences in sound perception across electrodes, suggesting significant channel-to-channel variability, which appears to correlate with CI mapping settings.

These preliminary findings suggest that both testing approaches might provide valuable insights into frequency-to-place mapping and sound quality judgments in CI users. Further investigations are ongoing to examine the relationship with specific frequency-to-place factors. These methods show promise as clinical tools to guide CI setup adjustments, enhancing sound quality perception for CI users.