International Congress on Cochlear Implants and Other Auditory Implantable Technologies edition:11th location:Stockholm, Sweden date:30 June - 3 July 2010
Background: Bilateral cochlear implants (CI) may offer deaf people a range of advantages compared to unilateral CI. However, speech perception in noise is mainly facilitated by better-ear effects and much less by interaural comparisons or true 'binaural' hearing. It is possible that binaural sensitivity exists but is not accessed due to technical limitations in electrical stimulation. With controlled, direct stimulation, binaural sensitivity has been demonstrated in bilaterally implanted adults (Long et al., 2006) and children (Van Deun et al., 2009). In these studies, a Binaural Masking Level Difference (BMLD) was measured for a narrowband signal presented to one electrode in each ear. In the present study, the BMLD experiments are extended to more clinically relevant signals and first steps are taken to bridge the gap between binaural detection of a sinusoid in a narrowband noise presented to one electrode and binaural speech perception in noise.
Methods: BMLDs are measured as the difference in detection threshold for a signal that is in phase (diotic) versus phase-reversed (dichotic) between two ears, in a diotic noise. Thresholds in both conditions are determined through an adaptive 3AFC procedure. Stimuli are presented to three adjacent electrodes at each ear, and stimulus parameters (frequencies, bandwidths, interaural delays) are varied to investigate their influence on the BMLD.
Results: Data of 10 CI listeners will be presented. A recent pilot study with 4 children showed that multi-channel BMLDs can be measured, but are more variable than single-channel BMLDs and may more heavily depend on stimulus parameters such as the noise bandwidth.
Conclusions and learning outcomes: The results of these multi-channel experiments will indicate whether binaural sensitivity can be supported in bilateral CI users by coordinating the stimulation at both ears and may have implications for future development of (binaural) speech processors.