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.