Speech, Timbre, and Pitch Perception in Cochlear Implant Users With Flat-Panel CT-Based Frequency Reallocations: A Longitudinal Prospective Study.

Hypothesis: To determine whether chronic use of experimental computed tomography (CT)-based frequency allocations would improve cochlear implant (CI) user performance in the areas of speech and music perception, as compared to the clinical default frequency mapping provided by the CI manufacturer.

Background: CIs utilize default frequency maps to distribute the frequency range important for speech perception across their electrode array. Clinical default frequency maps do not address the significant frequency-place mismatch that is inherent after cochlear implantation, nor the variability between individual anatomy or array lengths. Recent research has utilized postoperative high-resolution flat-panel CT imaging to measure the precise location of electrode contacts within an individual's cochlea, in order to generate a custom frequency map and decrease the frequency-place mismatch.

Methods: A cohort of 10 experienced CI users (14 CI ears) was recruited to receive CT scans and then use an experimental CT-based frequency map for 1 month. The efficacy of these maps was measured using a battery of speech and music tests.

Results: No change in speech or music performance between the Experimental and Clinical Maps was found at the group level, although there was large variability within the cohort. Greater benefit from the Experimental Map on speech in quiet tasks was correlated with better electrode array alignment in the apical (low frequency) region (rho14 = -0.55 to -0.72, p < 0.05).

Conclusion: This application of strict CT-based mapping was most beneficial for CI users with the least amount of apical-mid array frequency-place mismatch, and least beneficial for CI users with overly deep or shallow insertions. Results may be limited by long acclimation periods to clinical default frequency maps prior to CT map usage, intervention bias, and small sample size.