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Binaural timing sensitivity in multiple electrode stimulation

Authors Egger, K.
Year 2017
Thesis Type Doctoral thesis
Topic Psychoacoustics
Abstract Binaural hearing is important in everyday life. Listening with two ears facilitates the localization and segregation of sound sources. Accordingly, bilateral cochlear implantation has become the standard treatment for binaural severe-to-profound hearing loss. Listeners with bilateral cochlear implants (CIs) are able to regain some basic left-versus-right localization ability and show benefits in speech perception. Nevertheless, the CI listeners' performance in sound localization and speech understanding in noise is still limited compared to normal-hearing listeners. It is assumed that the limitations in performance are at least partly due to the poor sensitivity to interaural time dierences (ITDs). An ITD describes the delay between the signals arriving at the two ears when sound is coming from the side and arises because of the pathlength dierence between the ears. It can be assumed that the CI listeners' low sensitivity to ITDs is to some extent linked to the restricted access to ITD cues due to their suboptimal encoding with current bilateral CI systems. Therefore, this thesis focused on the systematic investigation of ITD sensitivity in electric hearing, with the emphasis on stimulation at multiple electrodes at low pulse rates. Overall, the results help to better understand the perception of binaural timing information with CIs and form a basis for the development of future stimulation strategies which potentially enable improved access to ITD cues for bilateral CI listeners. The main ndings suggest that CI listeners may benefit from combining consistent ITD information across multiple electrodes, provided that there is sufficient stimulus level and the stimulating electrode pairs are widely spaced. Further, it was shown that the ITD sensitivity deteriorates and the perceived auditory image widens when interaurally-uncorrelated pulse removal is applied to binaural pulse trains, as currently done in fine-structure coding strategies due to timing limitations imposed by the demands from stimulation at multiple electrodes. Last but not least, it was demonstrated that the loudness of the stimulus significantly affects the ITD sensitivity as well. While the sensitivity improves with increasing loudness up to an approximately medium (i.e., comfortable) level, higher loudness does not yield further improvement.
Supervisors Höldrich, R., Majdak, P.