Electrophysiological Correlates of Dichotic Streaming in Bilateral CI Users

Background: Previous work in normal hearing (NH) humans has shown selective attention to left versus right concurrent auditory streams are associated with specific neural markers: 1) increased “neural tracking” to the attend stream compared to the ignore stream and 2) alpha event-related synchronization (ERS) ipsilateral to the attend side. Neural tracking measures include cross correlation and temporal response functions between the EEG (electroencephalogram) and the speech envelope.

Objective: The purpose of this study was to examine whether similar relationships exist in bilateral CI users.

Methods: Two speakers positioned at +/- 45 degrees and at 1.5 meters away from the CI users were used for stimulus presentation. The stimuli consisted of 4 to 7 pairs of digits presented to each speaker. Prior to each trial, a cue indicated which side the participant was instructed to attend to. The number of digits and attend side varied randomly across trials. The task was to recall the last digit presented on the cued side. A 64-channel EEG (electroencephalogram) recorded while subjects performed the task. Temporal response functions between the speech envelope and the EEG were separately performed for attend and ignore stimuli. Time-frequency analysis was also separately performed.

Results: CI users performed the task at 80-90% behavioural accuracy. Neural tracking measures indicated that the attend stream evoked larger responses than the ignore stream. We also observed a cue-evoked alpha ERS in the ipsilateral hemisphere.

Conclusion: Our results indicate similar neural signatures in bilateral CI users to previously published data on normal hearing subjects.