Frequency-Following Response (FFR) in cochlear implant users: a systematic review of acquisition parameters, analysis, and outcomes.
Leonardo Gleygson Angelo Venâncio, Mariana de Carvalho Leal, Laís Cristine Delgado da Hora and 2 others
PMID 35081198WHAT IT FOUND
No standardised way to record the brainstem response to speech in cochlear implant users exists.
Parameters varied widely, and the implant's own electrical noise was rarely removed, so the reported differences from normal hearing cannot be trusted as clinical findings.
Key findings
01The review found no standardised protocol for recording this response in implant users, and only six small studies met the inclusion criteria.
02All included studies had a high risk of bias due to low methodological quality, and the authors could not pool the results into a meta-analysis.
03The implant's electrical artifact was rarely controlled for, so the observed differences in response timing and strength may reflect machine noise rather than neural processing.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Only six studies were found, all observational, with samples of 10 to 40 participants and no sample-size calculations. Every included study was rated high risk of bias, with poor description of participants and settings and no identification or control of confounding factors. Recording parameters varied so widely that the authors could not assess the effect of different protocols, could not run a meta-analysis, and could not rate the certainty of the evidence. Most studies did not remove the implant's electrical artifact or account for the delay the processor introduces, so the neural origin of the recorded responses is uncertain. Five of the six studies used only children, and ages ranged from 2 to 60 years across the whole set, so results do not describe either group well.
Declared interests
Funded by CAPES (Brazil), Finance Code 001, a government research-support agency. No commercial conflicts are declared, and no implant manufacturer is reported as having designed, analysed or written up the work.
The easy way to misread this
Do not read the delayed latencies and smaller amplitudes in implant users as proof of a neural speech-processing deficit. The review states the implant artifact may have overshadowed the neural response and that these results have not proved to be reliable, so the differences may be electrical noise rather than a patient finding.