Interaural time difference sensitivity with high rate electrical pulse trains in bilateral cochlear implant users

Abstract

Interaural time differences (ITDs) are an important cue for obtaining binaural hearing benefits. Bilateral cochlear implant (BiCI) users have shown poor ITD sensitivity when using clinical processors, but have some ITD sensitivity with carefully controlled stimuli presented using synchronized research processors. In BiCI users, low stimulation rates yield best ITD sensitivity, but declines as the stimulation rate increases. However, high rates are typically needed for good speech understanding, which poses a conundrum for maximizing the benefit of BiCIs. Aperiodic high-rate stimulation has been shown to promote ITD sensitivity. However, it is uncertain whether this improvement is due to changes in the loudness level, which may provide an envelope ITD cue. In this study, we tested this hypothesis by measuring ITD just noticeable differences (JNDs) with 4000-Hz electrical pulse trains. Pulse trains either had: (1) constant amplitude and rate; (2) aperiodic timing in the pulses; and (3) aperiodic timing + a random amplitude applied to each pulse. Results have implications in determining whether aperiodic high-rate stimulation can be useful for restoring ITD sensitivity. [Work supported by NIH-NIDCD (R01DC003083 to Ruth Litovsky) and NIH-NICHD (P30HD03352 to the Waisman Center).]