Implementing Short Interpulse Intervals (SIPIs) in Multi-channel Cochlear Implants

Abstract

Cochlear implants (CIs) are the only neuroprosthetic devices that can restore hearing to people with severe‐to‐profound deafness. Yet, bilateral CI listeners still struggle to exploit interaural time difference (ITD) cues for spatial hearing because the standard continuous interleaved sampling (CIS) strategy removes temporal fine structure, leaving only envelope ITDs. Prior attempts to reintroduce ITD cues—such as mixed rate, phantom cue, and envelope sharpening methods—failed to deliver additional ITD benefits without degrading speech quality in real time. The recently proposed Short Interpulse Interval (SIPI) strategy overcomes this trade-off by embedding sparse, low-rate pulses within an high-rate train, theoretically restoring microsecond-scale ITDs while preserving sound quality. Until now, however, SIPI had been tested only in single-channel settings. This research is the first to deploy SIPI on clinical multi-channel implants and evaluate its perceptual impact. Aim 1 assessed ITD sensitivity in eight experienced bilateral CI users for three SIPI pulse rates (50, 100, 200 pps) and three insertion methods (fixed, random, local maximum). Aim 2 compared phoneme recognition for each listener’s optimal SIPI setting versus standard CIS at two signal-to-noise ratios (+10 dB, 0 dB) and two binaural configurations (N₀S₀, N₀Sπ). The SIPI rate showed a significant main effect on lateralization accuracy, peaking at 50–100 pps and declining at 200 pps, while the insertion method had no significant main effect. The best SIPI configuration improved ITD discrimination by up to 22 percentage points relative to CIS. In speech testing, SIPI preserved baseline intelligibility (N₀S₀) and delivered significant additional binaural masking release of 11.2 % at +10 dB SNR and 6.5 % at 0 dB SNR. Gains were largest for stop consonants (which have abrupt temporal characteristics) and smallest for steady-state vowels. These findings showed that multi-channel SIPI can restore meaningful ITD cues without compromising speech quality, resolving a long-standing limitation of CI processing. This research indicated that the SIPI strategy has a promising future in clinical applications, providing CI users with both high intelligibility and improved spatial hearing.