Distortion of Spectral Ripples Through Cochlear Implants Has Major Implications for Interpreting Performance Scores.
Matthew B Winn, Gabrielle O'Brien
PMID 34966157WHAT IT FOUND
Spectral ripple scores above 2 ripples per octave are unreliable for cochlear implant users.
The device distorts these high-density signals, so a higher score does not prove better spectral resolution. Clinicians should ignore correlations involving these high thresholds.
Key findings
01For the Cochlear device, the critical limit for spectral aliasing is around 2 RPO, and the theoretical upper limit for complete saturation of the narrowest filter is 3.46 RPO.
02Scores above the limit might or might not indicate better resolution, and do not indicate that spectra with specific density can be discriminated.
03Correlation of ripple thresholds with word recognition reported by Winn et al. (2016) grew stronger when high ripple scores were omitted (r2 grew from 0.45 to 0.59).
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The analysis focused on Cochlear devices, though estimates for other manufacturers are provided. The simulation used idealized filters and did not account for all real-world processing steps like noise reduction or dynamic range optimization. The paper is a theoretical and retrospective analysis, not a new clinical trial with patients.
Declared interests
The authors declared no financial disclosures or conflicts of interest.
The easy way to misread this
Do not assume that a cochlear implant user who scores 5 RPO on a spectral ripple test has better hearing than one who scores 3 RPO. The device cannot accurately transmit signals above 2 RPO, so the higher score reflects signal distortion, not improved auditory resolution.