Sensitivity to interaural timing differences using the advanced combinational encoder strategy

Abstract

When listening through clinical processors, sound localization in bilateral cochlear implant (BiCI) users is highly variable, and some patients perform rather poorly. While this is often ascribed to lack of access to temporal fine-structure interaural timing differences (ITDs), the potential role of envelope ITDs is often disregarded. Furthermore, sensitivity to ITDs alone has not been closely examined with the commonly used Advanced Combinational Encoder (ACE) strategy. In theory, envelope ITDs could be encoded with ACE and some BiCI users may be sensitive to this cue to locate sounds, which may explain why some BiCI users have better localization performance. ITD just noticeable differences (JNDs) were measured in 9 participants, using a novel setup of presenting whole-waveform-delayed words through the auxillary port of clinical processors. Listening with ACE, ITD JNDs ranged from 105-680 µs (unmeasurable in one listener). Localization root-mean-squared error ranged from 19-68 degrees. However, ITD sensitivity and sound localization were not significantly correlated (ρ = 0.5, p = 0.17). The unexplained range of sound localization performance in BiCI users is likely due to distorted and inconsistent binaural cues that arise from uncoordinated device programming and signal processing across the two ears. [Work supported by NIH-NIDCD (R03DC015321 to AK and R01DC003083 to RYL) and NIH-NICHD (P30HD03352 to Waisman Center).]