Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Speech, Language & Hearing Sciences

First Advisor

Anu Sharma

Second Advisor

Kathryn Arehart

Third Advisor

Albert Kim

Fourth Advisor

Yuko Munakata

Fifth Advisor

Gail Ramsberger

Abstract

Background: In cross-modal reorganization, a well-known phenomenon that occurs in sensory deprivation, intact sensory modalities can recruit and repurpose cortices of deprived modalities. Cross-modal reorganization has been linked to behavioral outcomes in deaf, cochlear-implanted adults. However, there have been no efforts to directly investigate these phenomena in deaf children who receive cochlear implants, even though cross-modal reorganization could potentially shed light on the variability in speech and language outcomes observed in this population.

Purpose: The current study included the following aims: 1) To characterize maturation of cortical somatosensory evoked potentials using high-density EEG in normal hearing children, for use in comparison with children with cochlear implants; 2) To examine somatosensory-to-auditory cross-modal reorganization using high-density EEG in children with cochlear implants; 3) To investigate possible correlations between somatosensory-to-auditory cross-modal reorganization and speech perception in children with cochlear implants. We hypothesized that high-density EEG and estimation of the sources of cortical activity would reveal somatosensory cross-modal reorganization in children with CIs, and that these findings would be correlated with behavioral outcomes in these children.

Methods: Cortical somatosensory evoked potentials (CSEP) were recorded in response to vibrotactile stimulation of the right index finger in 5-19 year old children with normal hearing (NH) and cochlear implants (CI). Developmental changes were investigated by comparing CSEP latency and amplitude and cortical source estimates across age. Finally, results from a measure of speech perception in noise were correlated with CSEP responses in children with cochlear implants.

Results: Waveform morphology and cortical activation were stable across age in the NH group, though latency and amplitude comparisons across age revealed some developmental patterns for the NH children. CI children showed larger amplitudes and shorter latencies for some CSEP components, along with activation of auditory cortical areas in response to vibrotactile stimulation, suggestive of somatosensory cross-modal recruitment. CSEP waveform components were correlated with behavioral performance on a clinical measure of speech perception in background noise for CI children.

Conclusions: Overall, our data are suggestive of somatosensory cross-modal reorganization in children with cochlear implants, which may have bearing on their speech perception performance with these devices. Our findings indicate that somatosensory cross-modal reorganization may be a source of variability in CI outcomes, which deserves further investigation.

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