Frequency-to-Place Mismatch: Characterizing Variability and the Influence on Speech Perception Outcomes in Cochlear Implant Recipients.
Michael W Canfarotta, Margaret T Dillon, Emily Buss and 3 others
PMID 32205726WHAT IT FOUND
Default implant maps placed frequencies at different cochlear locations, with large individual variation.
For CI-alone users, better early word scores were linked to closer frequency matching and wider contact spacing, but five cases with mismatch above 9 semitones drove the result.
Key findings
01Frequency-to-place mismatch varied widely in CI-alone and EAS users, and partial insertions generally showed greater mismatch.
02For CI-alone users, smaller mismatch was associated with better word scores at 1, 3, and 6 months, and greater angular separation was associated with better scores at 1 and 6 months.
03The mismatch-word score association was not robust: removing five cases with mismatch above 9 semitones made it non-significant.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study measured existing implant positions and outcomes, so it cannot show that frequency-to-place mismatch caused poorer word recognition. The speech perception analysis included only CI-alone users who used default frequency filters and had no revision surgery or partial insertion, so it may not apply to patients whose maps were changed or whose arrays were partially inserted. The link between frequency mismatch and word scores was sensitive to five participants with mismatch above 9 semitones; after they were removed, the association was no longer significant. The predicted cochlear place frequency was based on an average spiral ganglion map, and the paper states that the exact frequency-to-place map for CI users remains unclear. Cochlear duct length estimates have current in vivo error of about 5%, and all imaging landmarks were determined by the first author. EAS outcomes involve residual acoustic hearing and electric mapping, and the paper states these effects are difficult to separate.
The easy way to misread this
Do not conclude that changing the map or choosing a longer array will improve speech perception. This study observed associations in people using default maps. The link between frequency mismatch and word scores disappeared when five cases with mismatch above 9 semitones were removed.