Date of Award

2022

Document Type

Thesis

Degree Name

MA in Speech-Language Pathology

Department

Communication Sciences and Disorders

First Advisor

Yan H Yu

Abstract

We examined the possible modulatory effect of tDCS on the automatic processing of speech sounds by evaluating the components of two ERP waveforms (P1-N1-P2 and T-Complex. The P1-N1-P2 components were measured at frontocentral sites F3, F4, C3, C4, Cz, and Fz while the T-Complex components were measured at temporal cortices T7 and T8. A 64-channel sensor cap from Electrical Geodesics, Inc was placed on each of the participants’ scalp. The 17 young adults (12 females, 5 males) sat comfortably during the EEG measurements within an electrically shielded and sound-attenuated booth while watching a silenced movie with subtitles delivered through a handheld tablet computer. The two auditory stimulus conditions were presented to each participant across two time periods (pre and post tDCS) using over-the-ear headphones at a comfortable listening volume. A total of 1000 standard trials were delivered for both Step 3 (/I/) Step 9 (/ℇ/) at a rate of 650 ms (interstimulus interval of 450 ms). The auditory stimuli were delivered using E-prime 2 software (version 270 2.0.10.356). The EEG data were acquired and digitized via Netstation software version 5.4. Each participant received 1.0 mA (milliampere) of electrical current for a total of 10 continuous minutes. The anodes were placed at F3, F4, T7, and T8 and the cathode was placed at Cz. Our results suggested that tDCS modules the automatic processing of speech sounds, but with asymmetrical responses across different brain structures. The relatively small effects or lack of effects of tDCS on some P1-N1-P2 and T-Complex components could be attributable to experimental parameters such as the intensity, duration, frequency, and location of the tDCS across the scalp. It is crucial to understand the relationship between tDCS and speech sound processing and performance given that the current environment is considering tDCS as both a treatment for a wide-range of disorders and deficits as well as a tool for enhancing learning.

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