In her keynote paper, Valian (Reference Valian2014) provides a comprehensive review of the literature that examines whether bilingual individuals outperform monolingual participants on various executive processing tasks. The author acknowledges that numerous factors contribute to the outcomes, such as variations in participants’ profile, differences in target functions, as well as variants of tasks and procedures. She also says in her review that, on the one hand, researchers use different tasks to measure similar functions; while, on the other hand, each of these tasks target somewhat different aspects of executive processing. The most widely used tasks, such as the Stroop or flanker tasks, measure several components of executive functions simultaneously.

In this commentary, I discuss two strongly related issues. The first one is the lack of comprehensive theoretical models that would integrate executive functions and language processing and reflect the dynamic nature of the bilingual experience. Although this issue has not been discussed in the keynote paper, it plays a major role behind the controversies in the bilingual literature and is closely related to the measurement problems. There are theoretical accounts of bilingual language processing (e.g., Kroll and Stewart, Reference Kroll and Stewart1994) and there are separate cognitive models of working memory and executive functions (e.g., Miyake, Friedman, Emerson, Witzki, Howerter & Wager, Reference Miyake, Friedman, Emerson, Witzki, Howerter and Wager2000) but there are no theoretical accounts that would integrate the cognitive and linguistic processes that determine the bilingual experience. Although Green's inhibitory control model (Abutalebi and Green, Reference Abutalebi and Green2007; Green, Reference Green1998) was developed to explain the interaction between language selection and inhibition, it does not provide a comprehensive model of executive functions and language processing. A comprehensive model would need to consider the role of other functions, such as shifting and updating, in addition to inhibition during language processing (Linck, Osthus, Koeth & Bunting, Reference Linck, Osthus, Koeth and Bunting2014). Thus, we are in need of theoretical models that show the links among different components of executive functions and bilingual language processing and capture the dynamic nature of these interactions across processes. Until then, we will have difficulty not only in understanding the basic interactions among executive functions and language processing but also in selecting the appropriate tasks to measure these associations. As Valian pointed out in her keynote paper, many of the currently used tasks measure various executive functions simultaneously. To provide an example, we reviewed the experimental literature on the Stroop task and found that Stroop himself claimed that the task measures interference (Stroop, 1935; MacLeod, Reference MacLeod1991, p. 164), whereas Mackin and colleagues suggest that it is an efficient measure of speed of processing (Mackin, Ayalon, Feliciano & Arean, Reference Mackin, Ayalon, Felliciano and Arean2010), while Houben and Wiers (Reference Houben and Wiers2009) suggest that the task measures automatic response inhibition. Furthermore, Kane and Engle (Reference Kane and Engle2003) propose that the Stroop interference is determined by goal maintenance and competition resolution, which in turn depends on working memory capacity. The fact that these tasks measure different processes simultaneously explains, at least to some extent, why the literature on the bilingual advantage is so contradictory. Those researchers who used different experimental manipulations, found more frequently superior performance in their bilingual groups compared to monolingual participants (e.g., Colzato, Bajo, van den Wildenber, Paolieri, Nieuwenhuis, Heiji & Hommel, Reference Colzato, Bajo, van den Wildenber, Paolieri, Nieuwenhuis, La Heij and Hommel2008; Hernandez, Martin, Barcelo & Costa, Reference Hernandez, Martin, Barcelo and Costa2013) than researchers who used global behavioral measures, such as the Simon, Stroop and flanker tasks. In well-controlled experiments we are able to manipulate only one aspect of executive control at a time, therefore a comparison across subtests may show the groups’ performance patterns for each targeted component of executive processing. In summary, there is an urgent need for comprehensive theoretical models of executive control and bilingual language processing and for theoretically driven experimental manipulations to clarify the areas in which bilingual individuals may show superior performance compared to monolingual individuals. If we had clear theoretical accounts describing how the different executive and language processes interact, then we could measure the different links with well-designed experiments where baseline measures of different processes could be compared to outcomes at more complex levels. Beyond the theoretical relevance, these questions also have significant clinical and educational implications.