Quantifying dynamic interaural level differences introduced in modulated electrical stimuli.

Abstract

Clinical mapping of bilateral cochlear implants (CIs) is often performed by measuring individual single-electrode currents that elicit threshold and comfortable loudness. This is done one ear at a time, where considerations for simultaneous bilateral stimulation are often disregarded. In contrast, synchronized bilateral stimulation of CIs in controlled research experiments often use constant-amplitude pulse trains to measure sensitivity to interaural level differences (ILDs) and interaural time differences. This is typically done using a single pair of subjectively pitch-matched electrodes, where the amplitudes of the electrical pulses elicit a near-comfortable loudness and produce a binaurally centered auditory image. Current clinical mapping of the processors do not consider possible ILDs introduced across the ears during simultaneous bilateral stimulation. Additionally, because loudness growth curves are often extremely variable across electrodes and ears, dynamic ILDs will possibly be introduced for modulated stimuli, like speech signals. Data will be shown that quantify the ILDs introduced by a typical bilateral clinical mapping, along with incoherence detection and binaural masking level difference threshold measurements, all in bilateral cochlear-implant listeners. Results will be considered in the context of theories regarding binaural processing and potential applications to clinical mapping strategies. [Support provided by the NIH Grant Nos. K99-DC010206 (J.G.) and R01-DC003083 (R.Y.L.).]