Dissertations, Theses, and Capstone Projects

Date of Degree

9-2025

Document Type

Master's Thesis

Degree Name

Master of Arts

Program

Linguistics

Advisor

Valerie L. Shafer

Subject Categories

Cognitive Science | Psycholinguistics and Neurolinguistics

Keywords

Bilingualism, Diphthongs, Event-Related Potentials (ERPs), Acoustic Change Complex (ACC), Speech Perception, Electroencephalography (EEG)

Abstract

This study examines how native phonological experience influences the brain’s response to speech sounds in Turkish-English late bilinguals and English monolinguals. We asked whether neural responses reflecting encoding of auditory information would be sensitive to language specific experience. Using event-related potentials (ERPs), and specifically, the Acoustic Change Complex (ACC) we measured neural responses to four stimuli, /u/, /ua/, /iu/, and /ia/, where vowel quality changes for three of these. A change from /u/ to /a/ or /i/ to /a/ within a syllable (as in [ua] and [ia]) represents a clear vowel quality shift. All participants were expected to show sensitivity to a change in vowel quality, reflecting sensitivity to acoustic-phonetic information. However, these sequences also violate Turkish vowel harmony constraints because for many words in Turkish, the vowel in a second syllable conforms to certain features (front/back/round) of the first vowel. This is called vowel harmony. If the ACC reflects phonological processing, we predicted that Turkish-English bilinguals would show different cortical responses than American-English listeners to this change in vowel quality. ERPs to the vowels were identified in two time-windows, 400–500 ms and 500–600 ms, reflecting the P2 and N2 fronto-central ERPs to the vowel change, which occurred at approximately 200 ms after stimulus onset. ANOVAs revealed significant Condition × Time Window interactions for both the /u/ vs. /ua/ and /iu/ vs. /ia/ stimuli. However, no group differences were observed. Post-hoc tests following up the Condition by Time Window interactions did not yield significant pairwise differences. These results suggest that both groups were sensitive to acoustic changes in vowel transitions, but this sensitivity was not influenced by native-language phonology. This is the first study to show that general auditory mechanisms rather than language-specific phonological information are reflected by the ACC. This finding is promising because it indicates that this ACC measure may serve as a clinical measure of auditory deficits in bilingual populations.

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