Test/Retest Variability of the eCAP Threshold in Advanced Bionics Cochlear Implant Users.
H Christiaan Stronks, Jan Dirk Biesheuvel, Johan J de Vos and 3 others
PMID 30946135WHAT IT FOUND
In Advanced Bionics cochlear implant users, noise-related repeated eCAP threshold measurements varied little, and the larger uncertainty came from extrapolating the response curve.
Key findings
01At the default 32 waveform averages, the median eCAP threshold variability was 2 to 3 μA when AP averaging was used.
02Doubling the number of waveform averages reduced the eCAP threshold variability by a factor of 1.52 and reduced background noise by a factor of 1.38.
03In the full data set, forward masking had eCAP threshold variability 2.33 times higher than AP averaging.
STILL TO COME
How it was doneWhat they found
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What it does not show
Only 13 subjects were analysed, and a 14th subject was excluded because no usable response curves were obtained. Only 31 of 39 electrode sites produced usable response curves. The subjects had relatively good speech perception, which may have produced smaller threshold variability than in poorer listeners. The study used a simulation that resampled the same recordings, not separate test and retest sessions. The reported variability reflects random background noise only. It does not include uncertainty from nonlinearities in the response curve or from extrapolating the curve. The finding of better precision toward the base came from a small sample and the authors say it may be a false positive. The authors did not adjust the statistical tests for multiple comparisons because the sample was small. The results apply only to Advanced Bionics devices, not to other cochlear implant systems. The study did not assess whether eCAP thresholds accurately match psychophysical thresholds.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not treat the 2 to 3 μA median spread as the full error of an eCAP threshold. The authors state that this noise-related test/retest variability is only a small fraction of the total variability introduced by extrapolating the amplitude growth curve.