An EEG study
Introduction
In day-to-day life, bilinguals manage two languages in one mind and switch language for a variety of reasons. For instance, bilinguals often encounter situations where they must switch into a language in response to situational demands or environmental cues (i.e., forced switching). They may also find themselves conversing with others who share the same languages, and thus, can freely switch between these languages at will (i.e., voluntary switching). According to Adaptive Control Hypothesis (ACH; Green & Abutalebi, 2013), the forced switching has been suggested to trigger (more) top-down control processes (such as monitoring, inhibitory control), whereas voluntary switching is at least partly driven by top-down control processes as a consequence of the decision process regarding whether or not to switch (Blanco-Elorrieta & Pylkkänen, 2016, 2017; Green & Abutalebi, 2013). However, sometimes, bilinguals exhibit a preference for using one language over another to name objects based on familiarity or cultural preference (i.e., natural switching). This latter switching situation is driven by lexical accessibility and has also been referred to as bottom-up switching (Dijkstra & van Heuven, 2002; Gollan et al., 2014; Kleinman & Gollan, 2016; Zhu et al., 2022).
Varying linguistic contexts have a wide influence on domain-general cognitive control. A growing body of research has repeatedly observed the modulation effect of linguistic contexts on domain-general control in both language production and comprehension (Green, 1986; Jiao et al., 2019, 2020; Linck et al., 2012; Liu et al., 2022a; Liu et al., 2022b). However, most of these have examined the relative “static” influence of linguistic contexts on domain-general cognitive control, such as behavioral performance (e.g., the flanker effect) and event-related potentials (ERPs), by comparing different contexts (Jiao et al., 2019, 2020; Linck et al., 2012; Liu et al., 2022b), or manipulating the task orders of language switching task and cognitive tasks (Liu et al., 2022a; Kang et al., 2017; Wu et al., 2018). In the present study, using a cross-task paradigm which flanker task was interleaved with language switching task trial-by-trial, we tried to reveal the dynamic modulation effect of various switching contexts on domain-general control.
There is a trial-to-trial upregulation effect in cross-task paradigm called cross-task conflict adaptation. Studies have found, compared with non-switching contexts (i.e., the single-language context), switching context (i.e., the mixed-language context) facilitated conflict resolution immediately (Jiao et al., 2019; Liu et al., 2022b; Wu & Thierry, 2013). Such conflict adaptation effect is well explained by the conflict monitoring theory (Botvinick et al., 2001), which argues that response conflict involved in incompatible trials causes them to be associated with a subsequent intensification of top-down control. Concerning the cross-task studies, this intensification adjustment is usually achieved by the dynamic adaptation of the increased cognitive demanding induced by language control to the subsequent domain-general control. Switching between language could heighten selective attention on task-relevant information and reduce interference from task-irrelevant information. That is, the cross-task conflict adaptation is a dynamically adaptive adjustment derived from homogeneous conflict resolution mechanisms (Liu et al., 2022b; Yuan et al., 2021). However, the relevant studies have yielded inconsistent findings.
In a seminal study by Wu and Thierry (2013), the flanker task was interleaved with target words. The authors manipulated the language context by intermittently presenting words in Welsh, English, or both. Results showed that in switching contexts, there was a reduced P3 effect for incongruent trials in the flanker task compared to the non-switching context. P3 amplitude, a positive deflection around 300-500 ms following stimulus onset, serves as a marker of response inhibition and is enhanced by response conflict (Clayson & Larson, 2011; Groom & Cragg, 2015; Kropotov et al., 2011; Smith et al., 2007). This reduced P3 effect emerged from the incidental presentation of words from two languages, enhancing executive functioning to assist in conflict resolution. Consistent with Wu and Thierry (2013), Liu et al. (2022) conducted a cross-task paradigm in an interpersonal situation and repeatedly found a reversed flanker effect (i.e., higher synchronization in incongruent trials relative to congruent trials) in switching context. The authors further argued that the conflict adaptation was merely reflected in the conflict situation induced by incongruent task-relevant stimulus features (Jiang et al., 2015; Liu et al., 2022b).
Nevertheless, findings on this issue have been mixed. In a series of ERP studies conducted by Jiao et al. (2019; 2020a; 2020b; 2022), a modified flanker task was interleaved with a language switching task in language production (i.e., picture-naming task) or comprehension (i.e., picture-word matching task). The results consistently revealed a larger N2 effect but a smaller P3 in switching contexts compared to non-switching contexts for both congruent and incongruent trials. The reduced P3 effects observed in both congruent and incongruent trials reflect the underlying mechanisms for conflict monitoring and conflict resolution (see also Jiao et al., 2019; Neuhaus et al., 2010). They suggested that ongoing monitoring and coordination during language switching should generalize equally to both incongruent trials, which induce conflict resolution, and congruent trials, which do not require interference inhibition (Coderre & van Heuven, 2014; Costa et al., 2009; Hilchey & Klein, 2011; Hannaway et al., 2017).
It seems that the empirical evidence fails to converge with respect to the conflict adaptation of language control on domain-general control. Furthermore, there is a lack of direct evidence to compare the impact of different switching contexts on conflict adaptation in cross-task paradigm. Previous cognitive studies primarily focused on the comparison between forced switching context and non-switching context, and failed to reach a consensus. Moreover, as aforementioned, there exist three switching modes in bilingual real-life, and the control processes that underpin these contexts are not fixed. Hence, these discrepancies motivate us to further investigate two main questions: (1) whether different switching contexts, regardless of the control processes involved, contribute differentially to domain-general control; (2) further, how different switching contexts dynamically modulate the cross-task conflict adaptation effect.
To this end, following previous research effort, the present study employed the cross-task paradigm of which flanker task was intermixed with picture-naming task trial-to-trial. Flanker trials were embedded in the forced, voluntary and natural switching contexts. In the forced switching context, participants were instructed to name the picture according to the language cues set by our experiment. While in voluntary context, bilinguals had full freedom to decide which language to use. Natural switching, on the other hand, is realized by the language-biased words acquired before the formal experiment (see Section 2.2 for a full description). The electrophysiological activities of the participants were recorded. Statistical analyses of behavioral response and brain activity, as well as Ridge regression prediction models were conducted to capture the dynamic and predictive effects of the three switching contexts on domain-general control. According to the introduced theoretical and empirical evidence, we hypothesized that if conflict adaptation effect in cross-task paradigm was merely dependent on higher cognitive demanding induced by previous trials, thus: (1) for both cognitive performance and predictive results, the forced switching context would promote the flanker’s performance compared to voluntary and natural switching contexts; (2) moreover, better performance in incongruent trials than congruent trials at least in the context of forced and voluntary contexts which involves the top-down control processes.