Alpha oscillatory activity reveals focused-attentional disparity between cochlear implant users and normal hearing listeners

Cochlear implants (CIs) allow hearing-impaired subjects to regain access to speech. However, the individual outcome variability remains high and unexplained. One contributing factor to the CI performance could be related to higher cognitive functions, which are not as well studied as in normal hearing (NH) populations. To study the cognitive processing in CI-users, in particular attentional processing, we compared the neural correlates of attention of a large cohort of CI-users (n = 37) to those of an age-matched group of NH-listeners (n = 37). The cognitive paradigm used here is a three-stimulus oddball paradigm in both passive and active listening conditions to isolate the attentional difference in unattended and attended task conditions. The addition of a third stimulus-type allowed us to specifically disentangling the attentional processing of task-relevant from the task-irrelevant stimuli. We expanded the previous ERP study by inspecting oscillatory activities. We localized the responsible brain areas and estimated local neural activities in three cortical regions: temporal transverse gyrus dorsolateral prefrontal cortex and inferior parietal lobule. We found alpha activity (8-12 Hz) to be the most relevant correlate of top-down auditory attention. The result on alpha activity suggests that CI-users may have directed their attention toward task-irrelevant stimuli, thereby impeding their focus on task-relevant stimuli. In sum, this study provides important insight into the cognitive attentional processing in CI-users; those may contribute in high listening effort and CI performance variability.