Binaural sensitivity and processing of envelope-based interaural difference cues by bilateral cochlear implant users with perilingual and postlingual onset of deafness

Cochlear implants deliver binaural cues primarily in the signal envelope through two unsynchronized sound processors, presenting challenges to bilateral cochlear implant (BiCI) users to (re)gain binaural hearing. Using a custom-designed acoustic complex to elicit multi-channel stimulation through the cochlear implant sound processors, this study measured sensitivity to interaural time difference (ITD) and interaural level difference (ILD) using a discrimination task while concurrently tracking eye gaze positions to reveal decision-making delays during binaural processing. Two groups of BiCI users were tested with either perilingual or postlingual onset of deafness. Results show all BiCI users exhibited ILD sensitivity and a majority (67% of the perilingual and 78% of the postlingual) demonstrated ITD sensitivity, though those with perilingual onset showed higher (poorer) ITD sensitivity compared to postlingual users. Additionally, ILD processing at suprathreshold magnitudes led to faster decision making as accuracy increased for both groups. However, ITD processing was less salient, with faster ITD processing observed only in the postlingual group. These findings provide insights into the differences in binaural processing in users based on the timing of deafness onset.