An objective measure, not requiring a behavioral response, of speech recognition performance in individuals with cochlear implants (CIs) would be beneficial in directing clinical recommendations. Neuroimaging can be such a measure but is difficult in the CI population. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that is viable for CI recipients. This dissertation began to examine the potential of fNIRS in this population by determining the effects of speech recognition performance and stimulus intensity level on fNIRS recorded cortical activation. We hypothesized that fNIRS responses would be correlated with both intensity level and speech recognition performance.
Thirteen adults with bilateral CIs and 16 adults with normal hearing were included in the study. Experiment one used signal-correlated noise to determine the effect of intensity level in the range of soft to loud speech (45-75 dB SPL). Experiment two used both signal-correlated noise and sentences presented in background babble at three different signal-to-noise ratios to determine the effect of speech recognition performance on cortical activity. fNIRS data were recorded in the left hemisphere.
The experiment one showed a positive correlation of auditory cortical activation with stimulus intensity level in both groups. In contrast, experiment two revealed a difference between the groups. The adults with normal hearing had stronger activation in the auditory cortex, inferior frontal gyrus, and the inferior parietal lobe with higher speech recognition. In contrast, the CI group had the opposite effect with stronger activation in those same areas with lower speech recognition. The stimulus level results are consistent with the literature and out hypothesis. The results of the second experiment are consistent with our hypothesis and the literature in only the normal hearing group. This is the first study to use neuroimaging for speech recognition in noise in individuals with CIs. Research is needed to further examine cortical activation patterns for speech recognition in noise in these two groups.
These results support the potential of fNIRS as a measure of speech recognition performance at a group level. The individual variability was large, however, and might limit the potential of fNIRS at an individual level.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-03082016-193820 |
| Date | 09 March 2016 |
| Creators | Sheffield, Sterling Wilkinson |
| Contributors | Rene H. Gifford, Baxter Rogers, G. Christopher Stecker, Daniel H. Ashmead |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-03082016-193820/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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