A Study of the Relationship Between Code Switching and the Bilingual Advantage
Bilinguals sometimes outperform age-matched monolinguals on non-language tasks involving cognitive control. But the bilingual advantage is not consistently found in every experiment and may reflect specific attributes of the bilinguals tested. The goal of this dissertation was to determine if the way in which bilinguals use language, specifically switching between languages within a conversation (code switching) or refraining from this behavior, plays a role in the sporadic bilingual advantage.
The bilingual advantage may arise from managing interference from one language in order to stay in the other, or from inhibiting one language in order to switch into the other. If language switching engages a general inhibitory mechanism to stop speaking in one language and switch to the other, bilinguals who frequently code switch ("switchers") might outperform bilingual "non-switchers" on non-language inhibition tasks. Alternatively, if the bilingual advantage results from frequent inhibition of interference from one language to stay in the other, non-switchers might outperform switchers.
The Assessment of Code-Switching Experience Survey (ACSES) was created to obtain an objective, rapid, and reliable measure for Spanish-English bilinguals' code-switching frequency. Then, event-related potentials (ERPs) of bilinguals with varied code-switching frequency were measured during a language task, lending validity to the survey. Semantic violations in code-switched and non-switched words were embedded in sentences as probes to determine how code-switches are processed and whether processing of code-switches is modulated by code-switching experience. The amplitude of a code switching positivity (typically elicited to a code-switch), but not the amplitude of the N400 (typically elicited to a semantic anomaly), was modulated by code-switching frequency. This indicates that code-switching experience affects processing of a code-switch but not semantic retrieval.
During Simon and Flanker inhibition tasks, which require suppression of interference from incongruent stimulus cues, a larger N2 ERP was elicited for incongruent versus congruent trials. The amplitude of this N2 congruity effect is typically correlated with inhibitory control ability. The effect was carried by the non-switchers; switchers and monolinguals did not differ. Thus, a general bilingual advantage was not found. Rather, non-switchers manifested a larger neural response linked to inhibitory control of interference, which may result from inhibiting interference in one language in order to stay in the other. However, no difference between switchers, non-switchers, and monolinguals was found on inhibition tasks that required simple response inhibition in the absence of interference. Thus, language production may differentially tap into existing cognitive control mechanisms that are specific to the way in which we are using language. I have interpreted the non-switcher interference suppression advantage in terms of recent studies demonstrating switching benefits in switchers and spatial benefits in bilinguals who use sign language. I suggest refining the definition of the bilingual advantage to include multiple aspects of cognition that are differentially affected by language experience.