Brain Responses to Silent Lip Reading in Normal Hearing, CI Users, and CI Candidates

Background: Previous work in human and animals have shown that deafness is associated with auditory cortex activation in response to visual stimuli. In CI users, greater degrees of auditory cortex activation to visual stimuli were associated with poor speech perception outcomes.

Objective: The purpose of this study was to examine whether similar relationships exist in CI users and those waiting for a CI.

Methods: Normal hearing (NH), CI users, and those waiting for a CI (“pre-operative”) were tested on a speech lip-reading paradigm using a silent movie as a stimulus. The movie consisted of a person uttering a single syllable animal lasting approximately 2.5 sec. The task was to watch the movie clip and indicate via keyboard the perceived word. A 64-channel EEG (electroencephalogram) recorded while subjects performed the task.

Results: Evoked responses (P1/N1) were observed to the onset of the movie. Brain source analysis revealed that in NH and CI users, the visual cortex was maximally activated. In the pre-op population, the peak activity occurred in auditory temporal lobe regions. Time-frequency analysis indicated a robust alpha desynchronization that localized to occipital cortex in all three subject groups.

Conclusion: Cortical evoked potentials and brain oscillatory activity represent different aspects of neural processing. Evoked potentials appear to represent early sensory processing and show an abnormal generator in the pre-op population. No differences were observed in the brain oscillations between the groups suggesting similar post-sensory cognitive neural networks.