INTRODUCTION: Since the majority of cochlear implant users have been provided with a single device, there is little information available to date to determine the impact on speech perception and sound localisation with two implants. This study aims to determine the benefits that bilaterally implanted children receive from HiRes® 120 in comparison to a unilaterally implanted control group.

METHODS: Congenitally deaf children aged between 18 months and 4 years are included in the study and randomly assigned to either unilateral or bilateral implantation. 48 subjects, 24 per condition, will be enrolled in total across the three participating centres. The assessments take place before implantation followed by sessions at 3, 6, 12, 18, 24, 36, 48 and 60 months after first fitting. All patients are tested on speech detection, discrimination and identification (in quiet and in noise) and on sound localization. They are also assessed via parental questionnaires and via clinical observation scales on speech production and communication.

RESULTS: Subject recruitment is ongoing. So far, fifteen subjects have been implanted, eight bilaterals and seven unilaterals. They have reached various testing sessions from pre-implant to 18 months. According to the preliminary data obtained from scales and questionnaires, subjects with two implants seem to perform better than those with one, especially after 6 months of implant use: the bilaterals are progressing faster along the CAP (Categories of Auditory Performance); the MAIS or IT-MAIS (Infant Toddler - Meaningful Auditory Integration Scale) shows they have more auditory interactions with the environment; their localization ability appears better from the Spatial Rating Scale of the SSQ (Speech Sound Quality).

CONCLUSION: These results suggest a general tendency towards the benefits of bilateral implantation but more subjects and long term data including speech test results are now necessary to confirm these preliminary observations.