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Cortical Temporal Processing in Cochlear Implant Users : Amplitude Modulation and Voice Onset Time

Han, JiHye, M.S.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234498

Abstract Details

2014, PhD, University of Cincinnati, Allied Health Sciences: Communication Sciences and Disorders.
Study I. N1 Responses to Amplitude Modulation Change: A Novel Method to Quantify Cortical Temporal Processing Objective: We examined auditory cortical potentials in normal hearing subjects to amplitude modulated (AM) stimuli as either a acoustic change complex (ACC) or as an onset burst of the AM stimuli. Methods: Auditory cortical potentials were recorded from scalp electrodes in ten normal hearing subjects in two conditions: (1) as a change (ACC) from white noise to 4, 40, 300 Hz AM, with varying AM depths of 100, 50, 25% lasting one second and (2) to AM busts (4, 40, 300 Hz) lasting one second. Subjects were awake and watching a movie. Results: The N1 response of the ACC was large to low frequency AM (4 and 40 Hz) and small to the 300 Hz change. The N1 to the AM burst was small at low frequency (4 Hz) and progressively increased as the AM rate increased. Dipole source analysis revealed a similar relationship as a function of AM rate, and similar magnitudes were seen in the left and right sided dipoles. In contrast to the dipole analysis, inverse source modeling showed substantial hemispheric asymmetry as well as prominent frontal sources. Conclusion: N1 responses to the ACC to AM change as a function of AM rate resembled a low pass filter function indicating poor sensitivity to high modulation rates and robust sensitivity to low modulation rates. This property is reminiscent of the temporal modulation transfer function. In contrast, the onset burst function with AM rate likely reflects the rise time of the stimulus. Significant differences were seen between inverse source modeling and dipoles suggesting that when there are multiple brain sources active, modeling with a single dipole may be overly simplistic. A striking right frontal source was observed 4 Hz ACC that is consistent with previous studies suggesting that the right frontal regions are associated with processing in the syllabic/prosody time scale. Significance: The ACC provides a novel approach to studying temporal processing at the cortical level that is not possible with typical transient stimuli. Study II. Auditory cortical activity in cochlear implant users to voice onset time Objective: To compare cortical auditory evoked potentials (CAEPs) to speech syllables varied in voice onset time (VOTs) between cochlear implant (CI) users and normal-hearing (NH) listeners. Methods: Ten CI subjects and 11 NH controls were tested on syllable identification tasks using a synthetic /ba/-/pa/ VOT continuum. CAEPs (N1-P2 complex) were recorded from scalp electrodes in `good’ and `poor’ cochlear implant groups, as well as NH group in response to /ba/-/pa/ continuum. Results: Compared to NH listeners and good CI users, poor CI users had more variable perception in temporal differences in /ba/-/pa/ VOT continuum. In addition, the N1 amplitudes decreased with the increase in VOT whereas no P2 amplitude change as a function of VOTs was shown for all groups. N1 and P2 latencies were prolonged for CI groups in response to stimuli with longer VOT durations, compared to NH group. N1-P2 peak-to-peak amplitudes and P2 amplitudes were significantly smaller for both good and poor CI groups than for NH group. Conclusion: The altered auditory cortical activity was reflected in CAEPs in CI user, suggesting the decreased neural synchrony and reduced responses of the auditory cortex. Based on findings from the good CI group who showed comparable categorical perception with NH control and decreased cortical responses, the CAEPs could be applied to identify which acoustic features are neurally coded. Significance: These data provide an insight into the potential CAEP as a clinical tool for measuring changes in temporal processing of VOTs for CI users.
Fawen Zhang, Ph.D. (Committee Chair)
Andrew Dimitrijevic, Ph.D. (Committee Member)
Chung-Yiu Chiu, Ph.D. (Committee Member)
Robert Keith, Ph.D. (Committee Member)
148 p.
Audiology
Temporal processing; Acoustic change complex; Amplitude modulation; Auditory evoked potential; Cochlear implant; Voice onset time

Recommended Citations

Citations

  • Han, J. (2014). Cortical Temporal Processing in Cochlear Implant Users : Amplitude Modulation and Voice Onset Time [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234498

    APA Style (7th edition)

  • Han, JiHye. Cortical Temporal Processing in Cochlear Implant Users : Amplitude Modulation and Voice Onset Time. 2014. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234498.

    MLA Style (8th edition)

  • Han, JiHye. "Cortical Temporal Processing in Cochlear Implant Users : Amplitude Modulation and Voice Onset Time." Doctoral dissertation, University of Cincinnati, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397234498

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.