A rapid measurement for the effect of interaural mismatch on interaural time difference sensitivity

Abstract

Cochlear implant (CI) users often have difficulties utilizing binaural cues such as interaural time difference (ITD) because of a mismatch in terms of the cochlear stimulation location in each ear. Methods for measuring this mismatch often rely on psychophysical approaches that can require hours of testing. The goal of this study was to evaluate a rapid method for measuring the effects of mismatch on ITD sensitivity. Seven normal hearing listeners were tested with a vocoder that simulated current spread. Participants were tested with a traditional adaptive ITD protocol and a rapid descending ITD protocol with fixed ITDs starting at 2000 μs and decreasing in two dB steps to approximately 50 μs. In both protocols, four stimuli were presented. The first and last stimuli always had an ITD of 0 μs. One of the two center stimuli had a non-zero ITD. Participants had to identify which had the non-zero ITD. The carriers were altered to simulate varying mismatch across ears. The preliminary results indicated a similar effect of mismatch for both protocols, with considerably shorter testing time for the descending ITD protocol. This suggests that the rapid descending ITD protocol is a valid method for assessing the effects of interaural mismatch.