Undergraduate Honors Theses

Thesis Defended

Spring 2017

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Speech, Language & Hearing Sciences

First Advisor

Anu Sharma

Abstract

Auditory deprivation, as in hearing loss, appears to tax the brain, resulting in changes in cortical resource allocation. One form of cortical resource allocation in hearing loss is cross-modal reorganization, whereby cortical resources in the deprived modality are recruited and repurposed for processing by other sensory modalities. Cross-modal reorganization has been proposed as a source of variability underlying speech perception in patients receiving cochlear implants (CIs). Previous studies have documented cross-modal recruitment of auditory cortex for visual and somatosensory processing in hearing-impaired children with CIs. However, changes within the auditory modality have not been documented alongside visual and somatosensory cross-modal changes within the same subject group. Thus, the goal of this study was to examine cross modal reorganization across all three sensory modalities within a single group of CI children (n = 10) using high-density EEG. Behavioral correlates of speech perception in background noise were also measured. Amplitude and latency of cortical auditory, visual, and somatosensory evoked potentials were analyzed and source localization was performed to visualize cortical activation patterns within the entire group of CI children, and across groups of CI children exhibiting good vs. poor speech perception. Results suggest widespread changes in cortical resource allocation in CI children in all three sensory modalities. Further, frontal cortex activation was observed in response to auditory and visual stimulation in CI children, suggesting that frontal areas may be recruited as a means to help compensate in speech perception and/or higher-order cognitive processing tasks. CI children with good speech perception did not show recruitment of frontal cortex or cross-modal recruitment by visual processing, while the children with poor speech perception did. Taken together, results of this study reflect widespread changes in cortical networks in CI children, and it appears that these changes are correlated with functional performance.

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