Speech Comprehension In Cochlear Implant Users Assessed With Evoked Potentials And Response Times

Cochlear implant (CI) recipients differ greatly in their rehabilitation outcomes, including speech understanding in noise. Some of this variability is related to brain changes associated with intact senses taking over cortical areas from stimulation-deprived senses. Numerous studies have demonstrated such cross-modal reorganization in individuals with untreated hearing loss. However, how this is affected by the regular use of hearing devices, such as CIs, remains unclear. The current study aimed to investigate these effects by measuring cortical responses reflecting comprehension abilities in experienced CI users and normal-hearing controls. Using multichannel electroencephalography, we tested CI users who had used their devices for at least 12 months, and controls matched in terms of age, sex, and handedness (N = 2 x 13). Cortical responses
reflecting comprehension abilities – the N400 and late positive complex (LPC) components – were evoked using congruent and incongruent digit-triplet stimuli. The participants’ task was to assess digit triplet congruency by means of timed button presses. All measurements were performed in speech-shaped noise 15 dB above individually measured speech recognition thresholds. Three stimulus presentation modes were used: Auditory-only, visual-only, and visual-then-auditory. The analyses revealed no group differences in the N400 and LPC responses. In terms of response times, the CI users were slower and differentially affected by the three stimulus presentation modes relative to the controls. Overall, these results indicate that experienced CI users need longer to comprehend speech. Furthermore, they suggest that response times can serve as a proxy for speech comprehension in CI users.