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abstract: Two groups of cochlear implant (CI) listeners were tested for sound source localization and for speech recognition in complex listening environments. One group (n=11) wore bilateral CIs and, potentially, had access to interaural level difference (ILD) cues, but not interaural timing difference (ITD) cues. The second group (n=12) wore a single CI and had low-frequency, acoustic hearing in both the ear contralateral to the CI and in the implanted ear. These `hearing preservation' listeners, potentially, had access to ITD cues but not to ILD cues. At issue in this dissertation was the value of the two types of information about sound sources, ITDs and ILDs, for localization and for speech perception when speech and noise sources were separated in space. For Experiment 1, normal hearing (NH) listeners and the two groups of CI listeners were tested for sound source localization using a 13 loudspeaker array. For the NH listeners, the mean RMS error for localization was 7 degrees, for the bilateral CI listeners, 20 degrees, and for the hearing preservation listeners, 23 degrees. The scores for the two CI groups did not differ significantly. Thus, both CI groups showed equivalent, but poorer than normal, localization. This outcome using the filtered noise bands for the normal hearing listeners, suggests ILD and ITD cues can support equivalent levels of localization. For Experiment 2, the two groups of CI listeners were tested for speech recognition in noise when the noise sources and targets were spatially separated in a simulated `restaurant' environment and in two versions of a `cocktail party' environment. At issue was whether either CI group would show benefits from binaural hearing, i.e., better performance when the noise and targets were separated in space. Neither of the CI groups showed spatial release from masking. However, both groups showed a significant binaural advantage (a combination of squelch and summation), which also maintained separation of the target and noise, indicating the presence of some binaural processing or `unmasking' of speech in noise. Finally, localization ability in Experiment 1 was not correlated with binaural advantage in Experiment 2. / Dissertation/Thesis / Ph.D. Speech and Hearing Science 2013

Although unilateral cochlear implants generally provide good speech understanding under quiet conditions, patients with unilateral cochlear implants frequently report difficulty in understanding speech in the presence of background noise and difficulty in localizing the source of sound. Since these two listening functions require binaural hearing in normal hearing individuals, there has been a growing interest in bilateral cochlear implants as intervention type for people with severe-to-profound bilateral hearing loss. This study investigated the outcomes of bilateral cochlear implants in all the adult recipients of the Pretoria Cochlear Implant Program. All the subjects with BCIs were asked to choose a significant other person to participate in the study. All the subjects (i.e. subjects with BCIs and their significant other people) were asked to participate in a semi-structured interview and to fill out a researcher-generated questionnaire. The subjects with BCIs also underwent audiometric testing. The majority of the subjects with BCIs were found to demonstrate improved ability to understand speech in the presence of background noise and, to some extent, in their ability to localize sound sources. As both quantitative and qualitative methods were used to determine the outcomes, it could be demonstrated that the majority of adult bilateral cochlear implant recipients gain from the auditory benefits in everyday listening situations. The majority of subjects and their significant other people conferred that their improved auditory skills allow them to be more participative in social, cultural, and other activities, which add to the quality of their lives. / Dissertation (MCommunication Pathology)--University of Pretoria, 2009. / Speech-Language Pathology and Audiology / Unrestricted

Thesis (MAud (Interdisciplinary Health Sciences. Speech-Language and Hearing Therapy)--Stellenbosch University, 2008. / Individuals are increasingly undergoing bilateral cochlear implantation in an attempt to benefit from binaural hearing. The main aim of the present study was to compare the speech recognition of children fitted with bilateral cochlear implants, under binaural and monaural listening conditions, in quiet and in noise. Ten children, ranging in age from 5 years 7 months to 15 years 4 months, were tested using the Children’s Realistic Index for Speech Perception (CRISP). All the children were implanted with Nucleus multi-channel cochlear implant systems in sequential operations and used the ACE coding strategy bilaterally. The duration of cochlear implant use ranged from 4 years to 8 years 11 months for the first implant and 7 months to 3 years 5 months for the second implant. Each child was tested in eight listening conditions, which included testing in the presence and absence of competing speech. Performance with bilateral cochlear implants was not statistically better than performance with the first cochlear implant, for both quiet and noisy listening conditions. A ceiling effect may have resulted in the lack of a significant finding as the scores obtained during unilateral conditions were already close to maximum. A positive correlation between the length of use of the second cochlear implant and speech recognition performance was established. The results of the present study strongly indicated the need for testing paradigms to be devised which are more sensitive and representative of the complex auditory environments in which cochlear implant users communicate.