  Sensitivity to ITDs is important for sound localization. Normal-hearing
listeners benefit from across-frequency processing, as seen with improved ITD
thresholds when consistent ITD cues are presented over a range of frequency
channels compared to when ITD information is only presented in a single
frequency channel. This study aimed to clarify whether cochlear-implant (CI)
listeners can make use of similar processing when being stimulated with
multiple interaural electrode pairs transmitting consistent ITD information.
ITD thresholds for unmodulated, 100-pulse-per-second pulse trains were measured
in seven bilateral CI listeners using research interfaces. Consistent ITDs were
presented at either one or two electrode pairs at different current levels,
allowing for comparisons at either constant level per component electrode or
equal overall loudness. Different tonotopic distances between the pairs were
tested in order to clarify the potential influence of channel interaction.
Comparison of ITD thresholds between double pairs and the respective single
pairs revealed systematic effects of tonotopic separation and current level. At
constant levels, performance with double-pair stimulation improved compared to
single-pair stimulation, but only for large tonotopic separation. Comparisons
at equal overall loudness revealed no benefit from presenting ITD information
at two electrode pairs for any tonotopic spacing. Irrespective of
electrode-pair configuration, ITD sensitivity improved with increasing current
level. Hence, the improved ITD sensitivity for double pairs found for a large
tonotopic separation and constant current levels seems to be due to increased
loudness. The overall data suggest that CI listeners can benefit from combining
consistent ITD information across multiple electrodes, provided sufficient
stimulus levels and that stimulating electrode pairs are widely spaced.
