Thursday, Feb. 16th, 2017
It is well documented that bilingual speakers, regardless of age, exhibit enhanced cognitive control capacity (e.g., interference control) as compared with their monolingual peers. Behavior and imaging studies suggest that these effects are the result of a shared neural network recruited by both linguistic processing and general-purpose cognitive control in bilinguals. The majority of studies on bilingual cognitive control examine two groups—an early bilingual group (individuals who have been exposed to two languages from a very early age) vs. a monolingual control group. Late bilinguals (i.e., people who acquire a second language later in life) are often excluded in studies of bilingual cognitive control. Yet, it is precisely this population that makes up the majority of bilinguals in United States. This dissertation study compares an early bilingual group with two late bilingual groups in order to examine whether the cognitive processing advantage observed in bilinguals was associated with age of acquisition (AOA) or language proficiency. Data on cognitive control capacity were collected through three lab tasks that measured working memory capacity (WMC), response inhibition, and interference control, respectively. Results found that successful inhibition of prepotent responses was associated with higher WMC, later AOA, and higher language proficiency, while successful interference suppression was associated with higher WMC, earlier AOA and higher language proficiency. An efficient speed-accuracy trade-off pattern was also observed in early bilinguals. Findings from this study are discussed under the framework of the adaptive control hypothesis.