Evaluating the use of Bunched-up pulses for objective determination of thresholds in Cochlear Implants Users

International audienceFitting a cochlear implant (CI) to a patient requires to determine detection thresholds and comfortably loud levels for all CI electrodes. This process is difficult to achieve behaviorally in infants, urging researchers to find alternative objective methods, such as electrically-evoked auditory brainstem responses (eABRs). Although eABR thresholds for low-rate pulse trains correlate strongly with behavioral thresholds measured at the same rate, this correlation is much weaker with behavioral thresholds measured at higher rates, such as used in clinical CIs. This weak correlation is probably due to the fact that short-time constant temporal processes influence detection thresholds. We recently introduced bunched-up-pulses (BUPS) as an alternative stimulus to measure eABRs in CI subjects in order to capture the contribution of some of these temporal processes. BUPS stimuli consist of groups of n ?bunched- up? pulses repeated at a low frame rate. Here we evaluate the hypothesis that eABR thresholds obtained for a BUPS stimulus with n=12 could be used as a predictor of clinical thresholds. 15 MED-EL cochlear implant recipients were tested on two electrodes (apical and medial one). For each electrode, behavioral thresholds were measured for the clinical stimulus, and for BUPS stimuli with n=1 and n=12. Results show that eABR thresholds are significantly closer to clinical psychophysical thresholds for n=12 compared to n=1. This suggests that eABRs to BUPS capture some aspects of short-time temporal integration. Across-subject correlations between eABR thresholds for BUPS and clinical thresholds were also significant for both electrodes and for both types of stimuli (n=1 and n=12). However, the correlation was not stronger for n=12. This suggests that additional temporal integration processes occur at a higher stage of the auditory system than the generation site of the eABR. In order to locate this mechanism, additional measures of cortical responses are currently under study