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Introduction
Currently prevailing theories of bilingual language processing propose that words from both of a bilingual's languages share common conceptual representations and that lexical access is non-selective, meaning that both languages are activated in parallel during language processing (Dijkstra & van Heuven, 2002; Green, 1998; van Heuven & Dijkstra, 2010). Evidence for this non-selective access comes from research demonstrating significant effects of the second language (L2) on processing in the first language (L1; see reviews in Brysbaert & Duyck, 2010; Dijkstra & van Heuven, 2002; Kroll, Bobb & Wodniecka, 2006; Kroll, Dussias, Bogulski & Valdes Kroff, 2012). This evidence demonstrates that the non-target language can interfere with the target language during production or comprehension, even in completely monolingual contexts. Thus, bilinguals cannot completely 'turn off' one language: both are activated in parallel and can interact with each other, to the detriment, or advantage, of the bilingual language processing system.
The parallel activation of both languages in bilingual language processing necessitates executive control mechanisms in order to manage these cross-linguistic influences. Executive control is a key feature of the human cognitive system, referring to a variety of cognitive situations in which distracting information must be ignored, a specific response must be inhibited, or one must execute cognitive flexibility by switching between task goals. These processes require a number of cognitive functions including working memory, decision making, task maintenance, response selection and/or suppression, conflict detection/resolution, and inhibitory control. For example, task- and goal-switching paradigms assess cognitive control by indexing the ability to overcome the previous task goal. The flanker task (e.g., Bunge, Dudukovic, Thomason, Vaidya & Gabrieli, 2002; Eriksen & Eriksen, 1974; Luk, Anderson, Craik, Grady & Bialystok, 2010), which is utilized in the current study, presents directional arrows surrounded by other arrows that either point in the same direction (a congruent condition) or the opposite direction (an incongruent condition). Incongruent conditions generally elicit longer response times (RTs) than congruent or control trials. The difference in RTs between incongruent and congruent conditions (the flanker effect) or incongruent and control conditions (the interference effect) provides a measure of the ability to overcome cognitive conflict.
A number of brain areas are involved in executive control, mainly localized to the prefrontal and parietal cortices (see Nee, Wager & Jonides,...