Relationship Between Peripheral and Psychophysical Measures of Amplitude Modulation Detection in Cochlear Implant Users.

Only eight cochlear implant users were tested, and the authors note that small sample sizes can make significant correlations hard to detect. Some electrodes were excluded because ECAP recordings had excessive artifact, so some participants contributed only two electrodes. The nerve response measurements used a 15 ms stimulus, while the listening measurements used a 300 ms stimulus, so the two measures were not made with identical stimulus durations. Only four modulation frequencies were tested, and none were below 100 Hz, so a clear psychophysical cutoff frequency could not be determined. Correlations between nerve responses and perception were affected by participant S19L, who had unusually low thresholds and high nerve responses, and removing this participant changed the significant correlations. The modulation depth used for nerve responses varied across electrodes and participants because it was set from each person's threshold and uncomfortable level. Different pulse widths were used for some participants to meet voltage compliance limits, although each participant's peripheral and psychophysical measures used the same pulse width. Stimulus artifact was difficult to remove completely, data from some recordings were discarded, and other waveforms may still have had residual artifact. Speech perception was not correlated with modulation detection or growth function slope, in contrast to some earlier studies, so the relationship to everyday hearing is not established. The study did not test an intervention or programming change, so it cannot show that any treatment improves modulation detection or speech.

The supplied text does not include a conflict-of-interest or funding declaration. The methods note that participants had Cochlear Ltd. implants, Custom Sound EP was commercially available from Cochlear Ltd., and Cochlear Ltd. provided a research patch.

Do not conclude that stronger peripheral nerve responses to fast modulation mean better speech perception or that increasing modulation frequency will improve cochlear implant hearing. The listening thresholds were worse at high modulation rates, the peripheral and perceptual trends were opposite, and speech perception was not correlated with modulation detection in this small study.