ITD sensitivity provided to bilateral cochlear implant listeners by a mixed-rate, real-time capable processing strategy

Abstract

Bilateral cochlear implant (CI) listeners have limited access to interaural time differences (ITDs) at low frequencies in part because clinical processors do not coordinate the timing of stimulation across the ears. Further, clinical strategies, which are optimized for good speech reception, operate at stimulation rates that are too high [∼1000 pulses per second (pps)] to enable ITD sensitivity from the timing of pulses. Our newly developed, real-time capable sound coding strategy, delivered using a bilaterally synchronized research processor, enables binaural coordination and pulse-timed ITD encoding. We employ a “mixed-rate” stimulation approach by maintaining the capacity to provide speech or envelope ITDs on high-rate channels while simultaneously providing ITDs in the pulse timing on low-rate (100 pps) channels. We hypothesized that a mixed-rate strategy encoding both high-rate envelope ITDs and pulse ITDs would yield better ITD sensitivity than a strategy encoding pulse ITDs or high-rate envelope ITDs only. This hypothesis was tested by measuring the perceived range of lateralized auditory images in bilateral CI listeners. Preliminary results indicate listeners may have ITD sensitivity with all conditions, though the mixed-rate strategy can provide better ITD sensitivity in some listeners. This demonstrates the potential of the mixed-rate strategy for improving binaural hearing outcomes.