4. Discussion
Language control exhibits its adaptability in two primary ways: firstly,
it can flexibly implement a set of cognitive control processes to meet
the demands of varying interactive contexts; secondly, it can
dynamically adjust to subsequent cognitive control processes, a
phenomenon commonly referred to as the cross-task conflict adaptation
effect. However, the available evidence is mostly incomplete and far
from conclusive. Manipulating switching contexts that approximates
switching situations in bilinguals’ daily lives, the present study aims
to investigate how the varying switching contexts modulate cross-task
conflict adaptation effect. Our findings yielded the following insights:
1) natural switching contexts caused a smaller N1 effect in
switch-incongruent trials compared to forced and voluntary switching
contexts; 2) the cross-domain interaction on the P3 effect, however,
revealed an atypical flanker effect in forced switching contexts only,
and P3 amplitude of incongruent trials in forced switching contexts was
smaller than both natural and voluntary switching contexts; 3) further,
the prediction models revealed robust brain-brain relationships between
language control and cognitive control in the forced switching context
only for both congruent and incongruent trials; 4) specification curve
analysis confirmed this predictability generalized to the behavioral
performance (i.e., RTs of congruent trials). Collectively, our findings
indicate the modulation effect of switching contexts on cross-task
adaptation effects. Especially, the forced switching context profoundly
exhibited a predictive effect on the domain-general control processing
in both conflict and non-conflict situations.
Our first research question concerned whether cross-task conflict
adaptation effect varied among distinct switching contexts. Although no
behavioral differences between the three contexts were found, the
results of the N1 and P3 components confirmed the differential effects
of the three switching contexts on domain-general cognitive control,
especially the forced and natural switching contexts. More specifically,
for N1 effect, switch-incongruent trials in the natural switching
context showed a smaller N1 compared to both the forced switching
context and voluntary switching context. However, there was no
significant difference between voluntary and forced switching context.
Instead of the N2 effect observed in previous studies (Bartholow et al.,
2005; Folstein & Van Petten, 2008; Jiao et al., 2019; Kopp & Mattler,
1996; Van Veen & Carter, 2002), a negative ongoing waveform in the
early time window of 120-220 ms was elicited in our study, which we
preferred to define as N1 effect. The N1 effect is assumed to be
indicative of persistent covert visual attention control and sensitive
to the level of visual attention intensity on the target stimuli (Di
Russo). The greater N1 amplitude for incongruent trials in forced and
voluntary switching contexts relative to corresponding condition in
natural switching context implied more attention allocated to the
conflict situation in the contexts of forced and voluntary switching
(Luck et al., 2000). This concentrated attention on conflict situation
may be indicated as an efficient harbinger of conflict adaptation (Liu
et al., 2022b; Yuan et al., 2021). The reduced N1 effect in
switch-incongruent trials in natural switching contexts compared to
forced and voluntary switching contexts suggests that brain activity in
the former indeed stays at a lower functional level.
Furthermore, the P3 amplitude of incongruent trials in the forced
switching context was smaller than both natural and voluntary switching
contexts. Importantly, an atypical flanker effect was detected on the P3
effect in the forced switching context, whereas such effect was not
found in the other two switching contexts. This pattern is consistent
with previous studies (Hsieh & Lin, 2014; Jiao et al., 2020a; Wu &
Thierry, 2013). In the pure flanker task, incongruent trials induced a
larger P3 effect compared to congruent trials, which has been
interpreted as a ‘leakage’ of response inhibition ability on the trials
involving conflict (Groom & Cragg, 2015). Nevertheless, our findings
indicated that constant monitoring of the appropriate language and the
local inhibition of the non-target language in forced switching context
resulted in a functional generalization of heightened inhibition and
monitoring capacities engaged in subsequent flanker trials. Unlike the
typical flanker effect, which indicates response competition in response
selection, the reversed flanker effect mirrors the enhancement of
perceptual processes (Hsieh & Lin, 2014; Rouder & King, 2003). These
findings suggest that forced switching may alleviate some cognitive
demands introduced by incongruent trials by strengthening the perceptual
differentiation to incongruent trials relative to congruent trials.
Bilingual participants were able to adaptatively generalize their
conflict monitoring and language control to domain-general cognitive
control, facilitated by more recruitment of inhibition and conflict
monitoring in the switching context. Similarly, in a dual-EEG study by
Liu et al. (2022), a reversed flanker effect was revealed in
mixed-language contexts, but not in single-L1 contexts. The authors thus
argued that the adaptation of language control was limited to a
situation involving similar control mechanisms.
Our second research question examined how the adaptive patterns
manifested in flanker trials. Concerning our predictive model results,
however, it is plausible to demonstrate that the cross-task conflict
adaptation effect is not limited to conflict situations. A set of RR
models using coding activities of language switching tasks across the
three contexts to predict processing in the flanker task revealed that
language control processing engaged in forced switching contexts
displayed the earliest and most stable (of all predictive models)
positive relationships in congruent trials. The positive correlation
emerged at -10ms before the congruent stimuli were presented, lasting
until 500ms. This suggests that forced switching offers cognitive
assistance for subsequent flanker tasks during early processing stages.
In the models for incongruent trials, negative brain-brain predictions
were detected starting at 272ms in forced switching context, suggesting
the effective enhancement of forced switching on conflict resolution.
The prediction outcomes indicate varying effects and strengths of forced
switching contexts on congruent and incongruent trials. Although in this
context, which relies on top-down control mechanisms such as conflict
monitoring, resolution, and inhibitory control, the contextual influence
differs notably between congruent and incongruent trials. The early
emergence of predictive relationships when processing congruent trials
suggests that the continuous monitoring of two activated languages in
forced switching contexts is swiftly generalized to executive control
processing, while inhibition exhibited a later effect. The specification
curve results corroboratively showed significant positive relationship
between the predicted values in the forced switching context and RTs of
congruent trials. However, no significant relationships were detected
for other specifications. It seems that the cross-task adaptation of
language control to domain-general cognitive control is reasonably
general and not limited to conflict situations.
As afore-introduced, previous studies have not reached a consensus. Some
studies suggest that this adaptation shifting was limited to conflict
situations (Liu et al., 2022b; Wu & Thierry, 2013), i.e.,
incongruent-specific facilitation, whereas other work has reported a
wider advantage for both incongruent and congruent trials (Jiao et al.,
2019; Liu et al., 2016). For example, in a behavioral study by Liu et
al. (2016), the performance of a group of bilinguals in a nonlinguistic
“faces” task was measured before and after completing a
language-switching task. Results showed that participants’ response
inhibition and interference suppression were both improved after
language switching. Similar results have been shown in research on
code-switching. For instance, Alder and Valdés Kroff (2020) used a
cross-task conflict-adaptation paradigm to examine whether reading
code-switched sentences would influence performance on subsequent
incongruent trials, and confirmed a behavioral enhancement introduced by
reading code-switched vs. non-code-switched sentences. The present
study, on the basis of previous research efforts, causally provides
predictive evidence for the cross-task adaptation of language control to
domain-general cognitive control. However, considering the predictive
effect in congruent trials were stronger and earlier than incongruent
trials, our findings, further substantiated through SCA analysis (a
significant brain-behavior relationship between predict value of
congruent trials and RTs in forced switching context only), suggest that
the promoting effect of forced switching on domain-general control
varies between congruent and incongruent conditions. The cross-task
adaptation from language control to domain-general control dynamically
adjusts the engagement of executive functions to adapt to current task
demands.
This finding is consistent with recent neuroimaging studies revealing
the overlap between language control and executive control, such as
conflict detection and monitoring, along with shifting and inhibitory
control (Abutalebi et al., 2012; D’Souza, & D’Souza, 2016; Hwang et
al., 2017; Wu et al., 2019; Yeo et al., 2016; Yuan et al., 2021). In a
study comparing the performance of English monolinguals, unimodal
bilinguals, and bimodal bilinguals (who acquired both English and
American Sign Language) in a flanker task, Emmorey and colleagues (2008)
found that unimodal bilinguals performed faster than monolinguals and
bimodal bilinguals, and that performance of bimodal bilinguals did not
differ from monolinguals. These findings traced the bilingual advantage
in executive control to bilinguals’ experience in switching languages
more frequently. Subsequent research has shown that a bilingual
advantage only emerged when the two languages were intermittently used
in mixed-language contexts compared to single-language contexts (Alder
and Valdés Kroff, 2020; Jiao et al., 2019; Jiao et al., 2020a; 2020b;
Liu et al., 2016; Liu et al., 2022b; Wu and Thierry, 2013; Yuan et al.,
2021). The constructs of language control and cognitive control share
multiple subsets, such as conflict monitoring and inhibition of
prepotent interference (Abutalebi et al., 2012; Blanco-Elorrieta &
Pylkkänen, 2016, 2017; Emmorey et al., 2008; Liu et al., 2022b).
Bilinguals need to trigger a stricter top-down control process depending
on the needs of forced switching contexts. Building upon these findings,
our study further indicates that different switching contexts distinctly
modulates the components engaged in a subsequent executive control task.