Binaural sensitivity in bilateral cochlear implant users and normal hearing listeners

Extraction of cues that underlie spatial hearing begins in the "binaural system." This dissertation examined binaural sensitivity in human listeners over a range of testing conditions and stimuli from a relatively realistic cocktail party environment, in which the stimuli were both highly variable and not readily amenable to simple analytic descriptions, to an electrical pulse train delivered to a single electrode pair in bilateral cochlear implant (BiCI) users at a known pulse rate, width and amplitude.;Chapters 2 and 3 examined speech intelligibility and spatial release from masking (SRM) in a cocktail party environment. The results of experiments reported in Chapter 2 did not support the hypothesis that speech intelligibility and SRM would increase with increasing predictability of the number or locations of maskers. Results of experiments reported in Chapter 3 supported the hypotheses of greater SRM with speech maskers than with noise maskers and diminishing growth of SRM in bilaterally symmetric arrays with increasing angular separation of maskers from the target within the frontal hemifield. Results were not consistent with predictions of existing models of SRM and binaural unmasking.;The experiments reported in Chapter 4 explored sensitivity to interaural timing differences (ITDs) and interaural level differences (ILDs) in a relatively large cohort of BiCI users with widely varying hearing histories. Results supported the hypothesis that sensitivity to binaural cues is subject to a critical period, and this was particularly evident for sensitivity to ITD. Across subjects, examples of good sensitivity to ITD or ILD could be found at the base, middle or apex of the electrode array. Chapters 5 and 6 explored effects of channel interactions on binaural sensitivity in BiCI users and in normal hearing listeners, respectively. Results supported the hypothesis that sensitivity to ITD of the probe would be degraded in the presence of a conflicting ITD, but in normal hearing listeners this only occurred when the onset delay between the click trains was 5 ms. Results of these experiments suggest that the effects of interactions on binaural sensitivity are primarily at a perceptual level.