Estimating the relative interaural place mismatch for bilateral cochlear-implant listeners

Abstract

Frequency-matched bilateral input is important for the optimum encoding of binaural cues to facilitate sound localization, auditory scene analysis, and speech understanding in noise. Current bilateral cochlear-implant (CI) programming procedures do not account for potential interaural place-of-stimulation mismatch. This study investigated whether a perceptual test of interaural-time-difference (ITD) sensitivity can effectively estimate relative interaural mismatch for bilateral CI listeners. Ten bilateral CI listeners were tested on a two-interval left-right ITD discrimination task. Loudness balanced 300-ms, 100 pulse-per-second constant-amplitude pulse trains were delivered to single-electrode pairs using direct stimulation. Measurements were made for five reference electrodes evenly distributed along the array in one ear, and for at least five closely spaced comparison electrodes in the other ear for each reference electrode. The pair with the smallest thresholds was assumed to be the most closely place matched. ITD sensitivity was variable across listeners, with thresholds ranging from 80-2000 μs. ITD tuning curves varied across and within listeners, ranging from widths of approximately one (sharp tuning) to eight electrodes (broad tuning). While cases with narrower tuning provide clear suggestions for frequency programming to minimize interaural mismatch, estimates of mismatch were difficult to ascertain for cases with broad tuning.