Dissertations, Theses, and Capstone Projects

Date of Degree

9-2024

Document Type

Dissertation

Degree Name

Ph.D.

Program

Speech-Language-Hearing Sciences

Advisor

Klara Marton

Committee Members

Mira Goral

Patricia Brooks

Rachel Schiff

Subject Categories

Cognitive Science | First and Second Language Acquisition | Other Social and Behavioral Sciences

Keywords

Bilingualism, Cognitive Flexibility, Task Switching, Cognitive Control, Language Dominance, Multilingual Diversity

Abstract

Lifelong bilingual individuals develop expertise in language-switching, requiring a delicate balance between cognitive stability—safeguarding goals from interference—and cognitive flexibility—adapting goals to changing demands. While some studies demonstrate the transferability of these skills to non-linguistic tasks, signifying bilingualism's impact on cognitive processes, others find no direct correlation between non-linguistic task-switching and bilingualism. Our study investigated the cognitive processes underlying bilingual speakers' performance on a switching task, exploring whether varying degrees of bilingual experience in older adults result in different tendencies towards stability (e.g., lower mixing cost and response congruency effect) or flexibility (e.g., smaller switching costs). By treating the bilingual experience as a continuum and examining how individuals adapt to changing task demands, we aimed to gain valuable insights into the specific cognitive processes affected by bilingualism.

The study focused on older participants with lifelong bilingual experience, varying in language use and diversity. Examining language dominance and diversity in older adults, who have used multiple languages throughout their lives, may reveal which aspects of the bilingual experience contribute to cognitive flexibility and stability. We expected that carefully designed task-switching manipulations and a detailed characterization of the bilingual experience would advance our understanding of the interplay between bilingual language control and cognitive control.

Participants (n=33) completed a self-reported questionnaire, providing data used to compute scores reflecting dominance in the language of the environment relative to a second language and an index of multilingual diversity. The cued task-switching paradigm involved infrequent and frequent switch-trial manipulations, with controlled variables such as the number of consecutive switch/stay trials and congruency, allowing for a nuanced examination of the processes required to complete this task.

Mixed-regression analysis results revealed that participants with high relative dominance scores, compared with participants with more balanced language experience, had larger switching costs and a greater response congruency effect. Further analyses indicated that these participants exhibited stability during task performance, with faster stay trials leading to larger switching costs and faster performance on congruent (compared to incongruent) trials leading to a larger congruency effect. This suggests that older bilingual adults, who use their second language less frequently, require consistent control to suppress their nondominant language, ultimately gaining more experience in situations resembling stay-trials, enhancing stability during task switching.

Interestingly, participants with high multilingual diversity scores were slower on stay trials in mixed blocks than participants with lower multilingual diversity scores. Bilingually diverse individuals, accustomed to flexibility, may have found repeating the same tasks more challenging than switching to another task, indicating an increase in interference. Keeping several tasks active can increase cognitive flexibility, but repeating a task when the now non-relevant task is still activated can interfere with goal completion. Bilingualism seems to variably affect flexibility and stability, suggesting an experience-based impact on cognitive control. Our findings underscore a robust association between lifelong bilingual language use and non-linguistic task-switching performance.

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