Browsing by Subject "cochlear implant"

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    Neural Correlates of Phonetic Learning in Adult Listeners with Cochlear Implants
    (2015-08) Miller, Sharon
    Speech perception is a product of an individual's linguistic experience. Postlingually deafened cochlear implant (CI) recipients, persons who acquired speech and language with normal acoustic hearing, need to learn to remap degraded electric inputs provided by the implant to previously learned language patterns. The mechanisms underlying the perceptual remapping and whether formal auditory training can promote phonetic learning in CI users remain unclear. This dissertation used behavioral and auditory event-related potential (ERP) methods to examine phonetic learning of the difficult /ba/-/da/ and /wa/-/ja/ speech contrasts in adult CI recipients. Behavioral and neural measures were collected before and after high variability identification training. Behavioral experiments employed identification and discrimination tasks, and the ERP experiments used an oddball paradigm to elicit the mismatch negativity (MMN) response associated with preattentive phonetic categorization. The results indicated substantial neural plasticity for phonetic learning in adult postlingually deafened CI listeners can be induced by high variability identification training. The training protocol significantly improved perception of naturally produced speech in postlingually deafened CI recipients, and listeners generalized their learning to unfamiliar talkers. Fine scale behavioral and neural measures suggest enhanced phonetic categorization skills supported the observed improvements in phonetic perception. These findings have potential clinical implications related to the aural rehabilitation process following receipt of a cochlear implant device.
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    Using Binaural Beat Sensitivity To Describe Mechanisms That May Enhance Binaural Interactions In Single-Sided-Deafness Cochlear-Implant Patients
    (2020-04) Dirks, Coral
    Patients with single-sided deafness (SSD) have difficulty localizing sound and understanding speech in noisy backgrounds. Currently, if treated at all, SSD patients may be fitted with devices that route sounds from the deaf side to the better ear. These devices have two primary limitations: (1) they decrease the signal-to-noise ratio when target signals originate on the side with the normal-hearing ear, and (2) they do not restore spatial hearing (e.g., Kitterick, Smith, & Lucas, 2016). Recently, some SSD patients have received a cochlear implant (CI) in their deaf ear (SSD+CI). The aim of this thesis was to investigate the outcomes from the intervention, to determine the mechanisms underlying any observed improvements, and to test a novel CI fitting method designed to optimize the interactions between the normal-hearing ear and the CI. Data from the first study indicated that localization and speech understanding may improve after implantation, but the improvements are generally small and are primarily mediated by head-shadow effects. The lack of greater benefits of spatial hearing and spatial release from masking in speech experiments may be due in part to the poor match of spectral location between the two ears. Current fitting strategies attempt to maximize speech perception in the implant alone. However, SSD+CI patients may benefit more from a CI fitting approach that best complements information from the normal-hearing ear by providing a closer match in terms of the tonotopic maps in both ears. The second study explored ways to assess between-ear tonotopic matches using binaural interactions produced by dynamic interaural time differences in the temporal envelope. The final study tested the newly derived maps in terms of their success in improving sound localization and speech in noise perception. Outcomes suggest that frequency-to-place matching alone does not restore binaural integration of the NH and CI ears. Future work should determine whether correcting other mismatches in the time and amplitude-mapping domains, in combination with frequency-to-place matching, will improve speech perception and spatial hearing outcomes.