The choice of stimulation strategy affects the ability to detect pure tone inter-aural time differences in children with early bilateral cochlear implantation

Objectives: To investigate if the interaural time difference (ITD) ability is dependent of stimulation strategy. To examine the correlation between ITD, interaural level differences (ILD) and the ability to localize different sounds. Methods: Thirty subjects aged 8-13 who were implanted bilaterally before 3 years of age were tested. Twenty of the subjects used processors programmed with fine structure (FS) strategy on both sides. ITD and ILD just noticeable difference (JND) of a 250 Hz pure tone was measured using their clinical processors. Furthermore, their ability to localize sound in the horizontal plane was measured using eye tracking. Results: Ten of the 20 subjects with FS obtained an ITD threshold compared to none in the group without FS (0/10). ILD JND was correlated to localization ability of the broadband {BB) sound. Mean absolute error of the localization of a low-frequency (LF) sound was larger than that of a BB sound. Conclusions: The ability to detect ITD was present only when the cochlear implant stimulation had FS. The LF sound was more difficult to localize than the BB sound and ITD ability of FS strategies did not affect the localization ability of either sound. A low ILD seems necessary to improve the localization ability.