Authors: Raymond Goldsworthy¹
¹University of Southern California
Background: Bilateral cochlear implant (CI) users typically exhibit poor sensitivity to interaural time differences (ITDs), largely due to degraded temporal fine-structure (TFS) encoding and limited exposure to consistent binaural timing cues. While laboratory systems can restore precise interaural synchronization, the extent to which users can learn to utilize these cues through extended experience remains unclear.
Method: We evaluated ITD sensitivity in bilateral CI users during a multi-week training protocol using synchronized research processors. Participants completed repeated adaptive ITD discrimination assessments at 110, 220, and 440 Hz without feedback, interleaved with training blocks at a single pulse rate that included feedback and performance-based progression. Thresholds were tracked longitudinally to analyze changes as a function of training exposure and stimulation rate.
Results: ITD discrimination thresholds decreased systematically with training, with the most significant and consistent improvements occurring at 110 Hz. Gains at mid-rate stimulation (220 Hz) were more variable and condition-specific, while high-rate stimulation (440 Hz) showed minimal improvement. Learning trajectories spanned multiple sessions, demonstrating gradual threshold reductions and partial generalization across conditions.
Conclusion: Extended exposure to synchronized TFS cues can enhance binaural temporal sensitivity in CI users, particularly at low stimulation rates. These results suggest that perceptual limitations in CI users may reflect a lack of consistent sensory experience as much as inherent encoding constraints. This supports the integration of structured, rate-specific training paradigms into future CI signal processing and rehabilitation strategies to improve spatial hearing outcomes.
