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Article

Working Memory as the Focus of the Bilingual Effect in Executive Functions

by
Jiejia Chen
1,2,
Zitong Li
3,
Zhiheng Xiong
4 and
Guangyuan Liu
1,2,*
1
School of Electronic and Information Engineering, Southwest University, Chongqing 400715, China
2
Key Laboratory of Cognition and Personality, Ministry of Education, Southwest University, Chongqing 400715, China
3
School of Foreign Language, BeiHang University, Beijing 100191, China
4
School of Humanities, Southeast University, Nanjing 211189, China
*
Author to whom correspondence should be addressed.
Behav. Sci. 2025, 15(2), 134; https://doi.org/10.3390/bs15020134
Submission received: 6 November 2024 / Revised: 23 December 2024 / Accepted: 20 January 2025 / Published: 26 January 2025
(This article belongs to the Special Issue Developing Cognitive and Executive Functions Across Lifespan)
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Abstract

:
The bilingual effect on executive functions (EFs) has garnered considerable attention, with most studies focusing on the visual domain and largely overlooking the auditory domain. Furthermore, research has predominantly concentrated on specific subcomponents of executive functions, with few studies systematically examining all three key subcomponents. This raises two important questions: (a) Is the bilingual effect specific to certain modalities (modality-specific), or a more general phenomenon (modality-general)? (b) Is the bilingual effect concentrated in a specific component of executive functions (process-specific), or does it extend to all three components (process-general)? To explore these questions, this study recruited monolingual Chinese and bilingual Chinese–English participants, using matched visual and auditory Stroop, N-back, and task-switching tasks to assess inhibitory control, working memory, and cognitive flexibility in both groups. The results showed that, after controlling for variables like intelligence, socioeconomic status, and age, bilingualism significantly predicted performance in both auditory and visual working memory tasks, explaining 34% and 19% of the variance, respectively. However, no evidence was found to support a bilingual effect in inhibitory control or cognitive flexibility. In conclusion, these results suggest that bilingual effects are not only process-specific (affecting only working memory) but also modality-general (providing advantages in both visual and auditory modalities).

1. Introduction

Executive functions (EFs) are a set of cognitive abilities that regulate people’s thoughts and behaviors (Chen et al., 2021; Diamond, 2013; Friedman & Miyake, 2017; Miyake et al., 2000). We rely on EFs to concentrate, switch between tasks, and suppress instinctive impulses in order to make rational choices. In other words, EFs are the cognitive foundation for managing daily life (Doebel, 2020; Nancy et al., 2008; Snyder, 2013). Individuals with weak EFs tend to have poor self-control and act impulsively, which can contribute to issues such as obesity, poor work performance, marital discord, and other self-management problems (Crescioni et al., 2011; Eakin et al., 2004). Since EFs are crucial for human development, improving them has become a widely discussed topic in psychology and neuroscience (Chen et al., 2020; Diamond & Ling, 2016; Frischen et al., 2021).
Learning a second language may be an effective way to improve executive functions (EFs) compared to other experiences, such as cognitive training with monotonous computer tasks. This cognitive advantage is referred to as the bilingual effect (Bialystok, 2017; Diamond, 2020; Thorell et al., 2009). The bilingual executive processing advantage hypothesis suggests that both language systems in the brain are activated when bilinguals process information. The brain then suppresses interference from the non-target language during this executive process, constantly monitoring, updating, and switching to the target language. This process likely involves a variety of cognitive functions, particularly EFs (Bialystok & Craik, 2022; Hannaway et al., 2019; Hilchey & Klein, 2011). Language use is one of the most intense, persistent, and integrated human experiences (Bialystok, 2017). Using language activates multiple brain regions, including the frontal, temporal, and parietal lobes (Bialystok & Craik, 2022; Friederici, 2011; Li et al., 2014). This extensive involvement of brain centers increases the likelihood that the experience-related effects of language use may generalize beyond language itself (Bialystok, 2017; Bialystok et al., 2012). Bilingual experience and EFs may recruit similar cognitive processes and brain networks, thereby facilitating the transfer of abilities between the two functions (Diamond & Ling, 2016; Miyake & Friedman, 2012).
However, research on the relationship between bilingual experience and executive functions (EFs) has produced inconsistent results, with some studies confirming a bilingual effect, while others have not (Anton et al., 2019; Blumenfeld & Marian, 2011; Keijzer, 2013; Privitera et al., 2022, 2023; Yang et al., 2018). EFs consist of three core components—inhibitory control, working memory, and cognitive flexibility (Diamond, 2013; Diamond & Ling, 2016). In terms of inhibitory control, Bialystok’s (Bialystok et al., 2014) study found that compared to monolinguals, bilinguals showed less interference in the visual Stroop task, suggesting an advantage in visual inhibitory control. However, recent studies have not found a significant difference in visual inhibitory control between bilinguals and monolinguals (Dick et al., 2019; Giguere et al., 2022). In terms of working memory, Anton et al. (2019) found that bilingual participants performed better in both visual and auditory reverse-order digit tasks compared to monolingual participants, suggesting that bilinguals have an advantage in both visual and auditory working memory. In contrast, other studies using the Working Memory Span Task revealed no visual working memory advantage for bilinguals (Keijzer, 2013; Ratiu & Azuma, 2014). For cognitive flexibility, the results of visual experiments are also controversial. Yang et al. (2018) found that bilinguals performed better in the Dimensional Change Card Sort task than monolinguals, indicating that bilinguals may possess stronger cognitive flexibility. However, Han et al.’s (2022) study found no relationship between visual cognitive flexibility and language switching ability.
To summarize, the inconsistent results of previous studies can be attributed to the following causes. First, although the auditory domain is more important in language acquisition and use than the visual domain, most studies have focused on the visual domain to examine the advantageous effects of bilingualism on executive functions (EFs). Few comparative studies on visual and auditory modalities exist. Most of this research has only examined the bilingual advantage in EFs within a single modality. Direct comparisons of the visual and auditory modalities are challenging due to differences in experimental paradigms, materials, procedures, and participants. As a result, the modality specificity or generality of this effect remains unclear. To our knowledge, no study has comprehensively examined the visual–auditory differences in the bilingual effect based on the three components of EFs (i.e., inhibitory control, working memory, and cognitive flexibility). Second, some studies did not appropriately control for additional variables that affect EFs, such as IQ and socioeconomic status (SES), which led to mixed effects from these extraneous variables in the bilingual effect (Antoniou, 2019; Paap et al., 2015; Xie & Pisano, 2019; Xie & Zhou, 2020). Specifically, IQ affects executive functions, with higher intelligence levels being associated with stronger executive functions (Xie & Pisano, 2019). Similarly, higher socioeconomic status (SES), which typically reflects better family conditions, is often linked to improved executive functions (Calvo & Bialystok, 2014). Third, studies used different criteria to select and assign participants as monolinguals or bilinguals (Bialystok et al., 2016; Zhou & Privitera, 2024). Moreover, most studies on bilingualism used self-report questionnaires to collect participants’ language information. However, the design and interpretation of such tools are vague and depend strongly on the validity of the participants’ subjective reports (Antoniou, 2019). These issues make cross-group comparisons difficult, and as a result, the relationship between bilingual experience and EFs remains unclear.
This study recruited bilingual and monolingual participants and investigated the relationship between executive functions (inhibitory control, working memory, and cognitive flexibility) and bilingual experience through auditory and visual tasks. The aim was to explore whether the bilingual effect on executive functions is modality-specific or modality-general, and whether it is process-specific or process-general. To address this, we matched the experimental procedures for both auditory and visual tasks to prevent potential interference arising from variations in the experimental design. Additionally, we incorporated a range of covariates, such as IQ, SES, and age, in our analysis to gain a more comprehensive understanding of the specific link between bilingual experience and executive functions. Furthermore, we used the outcomes of the International English Language Testing System, Class A (IELTS), and the College English Test Band 4 (CET-4, a national English proficiency test administered by China’s Higher Education Department) to measure participants’ proficiency in English as a second language (native Chinese). A language and social background questionnaire was also administered to assess the frequency of language use, which allowed for a more objective categorization of participants into bilinguals and monolinguals.
Based on this, this study systematically investigated the relationship between bilingual training and executive functions, focusing on the following two main research questions: Research Question a: Is the bilingual effect specific to certain modalities (modality-specific), or a more general phenomenon (modality-general)? If bilinguals outperform in either auditory or visual tasks, the bilingual effect on executive functions would be considered modality-specific. Conversely, if they outperform in both auditory and visual tasks, this would indicate a modality-general effect. Research Question b: Is the bilingual effect concentrated in a specific component of executive functions (process-specific), or does it extend to all three components (process-general)? If bilinguals demonstrate superiority in only one core component of executive functions (e.g., working memory) without a corresponding advantage in the other components, the bilingual effect would be process-specific. However, if the bilingual effect is observed across all three components, it would suggest a process-general effect.

2. Materials and Methods

2.1. Participants

In this experiment, 60 participants were divided into two groups: 30 bilinguals and 30 monolinguals. The bilinguals had a total IELTS score of 7.0 or above, indicating a good proficiency in English and the ability to communicate effectively in English, which improved the grouping validity. In contrast, all participants in the monolingual group failed the CET-4 test, scoring less than 350 out of 710, indicating a poor grasp of English and an inability to communicate in English.
All participants completed the simplified version of the Raven’s Advanced Intelligence Test (Arthur & Day, 1994) (12 questions, 1 point per question, with a total score of 12) and the Language and Social Background Questionnaire (Chinese version) (Anderson et al., 2018) to collect information about their bilingual experience (Table 1). Social background information included participants’ names, gender, age, and SES. Specifically, participants’ names were recorded solely for the purpose of matching their survey and behavioral experiment results. In accordance with privacy and confidentiality principles, all personal information was anonymized during data analysis. Gender was recorded as a categorical variable, with 0 for male and 1 for female. Age was reported by participants in years, rounded to the nearest integer. SES was measured by the highest level of education of their parents, scored on a 1–5 scale: “Elementary school or below” = 1; “Junior high school” = 2; “High school or vocational school” = 3; “University” = 4; “Postgraduate or above” = 5 (Chen et al., 2020).
All participants were right-handed, had no history of psychiatric or neurological illness, and were not taking medication at the time of the test. Participant data exceeding ± 3 standard deviations were excluded from the statistical analysis. This study was approved by the Ethics Committee of Southwest University, and the participants signed an informed consent form prior to the experiment onset and received a predetermined reward upon completion. After excluding four participants (one who failed to complete the experiment as required, and three whose results exceeded 3 standard deviations), twenty-eight participants from each group were included in the statistical analysis. Both groups were matched by age (t(54) = 0.65, p > 0.2), gender ( χ 2 (1) = 0.13, p > 0.2), SES (t(54) = 0.51, p > 0.05), and IQ (t(54) = 1.45, p > 0.05).

2.2. Materials

An experienced researcher conducted the experiment in a quiet laboratory and provided one-on-one guidance to the participants. Six well-known experimental paradigms were used to measure the three main components of executive functions (EFs) through visual and auditory channels: the visual Stroop test, auditory Stroop test, visual N-back task, auditory N-back task, visual task-switching test, and auditory task-switching test. The experiment was divided into three parts, with two tasks completed at a time (each lasting about 10–15 min), and a 15 to 20 min break between each part to prevent participant fatigue. The order of the six tasks was counterbalanced across participants. The participants completed the demographic information, language questionnaires, and intelligence tests after finishing the experimental tasks. The total duration of the experiment was approximately 2 to 2.5 h, including rest time.

2.2.1. Visual Stroop Task

The materials in the visual Stroop test consisted of 16 Chinese characters, which included the words “red”, “green”, “blue”, and “yellow” in four different colors. Stimuli were divided into word–color-consistent trials (congruent) and word–color-inconsistent trials (incongruent). Participants made judgments about the color of the word and ignored its meaning. In total, 160 trials were conducted, with 80 trials each for congruent and incongruent conditions. The instructions were presented before the experiment began. First, a black “+” appeared in the center of the screen for 500 ms. Next, a random blank screen flashed for 500–800 ms, and a stimulus appeared for 300 ms. The stimulus was followed by a blank response screen for 1000 ms and a random blank screen for 1000–1500 ms. The differences in accuracy and reaction times between the congruent and incongruent conditions represent the Stroop interference effect. A smaller effect indicates better inhibitory control in response to visual stimuli.

2.2.2. Auditory Stroop Task

The materials in the auditory Stroop test included eight pronunciations of the Chinese characters “big” and “small” at different volumes (70 dB/50 dB) in male or female voices. Based on whether the loudness matched the meaning, they were divided into consistent (congruent: 70 dB for “big” and 50 dB for “small”) and inconsistent trials (incongruent: 70 dB for “small” and 50 dB for “big”). The experimental process was the same as the visual Stroop test, and the presentation time for the sound stimulus was 300 ms. Before the main experiment, 30 college students with normal hearing were invited to evaluate the sound materials on a scale of 1–5. The results showed that all the sounds were clear and varied (M = 4.86, SD = 0.35), with neutral emotions (M = 4.80, SD = 0.41), and there was a significant difference in perceived volume between the two levels (M = 4.93, SD = 0.25).

2.2.3. Visual N-Back Task

The visual N-back task consisted of three blocks: 1-back, 2-back, and 3-back, presented in sequence. Each block included a practice session, followed by the formal experiment. A total of 180 trials were conducted, with 60 trials for each block. The procedure for each trial was as follows: the experimental instructions were presented at the start of the test, followed by a blank screen for 1000 ms, a visual stimulus for 300 ms, a black response screen for 1500 ms, and a random blank screen that lasted between 1000 ms and 1500 ms. Task accuracy (proportion of hits minus proportion of false alarms) under different working memory loads was used as the evaluation metric. Higher accuracy and shorter response times indicated stronger working memory performance under visual stimulation.

2.2.4. Auditory N-Back Task

The materials for the auditory N-back task consisted of the numbers 1–9 spoken in both male and female voices. The experimental procedure was the same as that of the visual N-back task, with a total of 180 trials, 60 trials in each block. All sound stimuli were clear, identifiable, and emotionally neutral, assessed using the same procedure as the auditory Stroop task.

2.2.5. Visual Task-Switching Paradigm

The materials for the visual task-switching paradigm consisted of visual presentations of the numbers 1–9. Participants were asked to respond to cues in two types of tasks. The ‘size’ cue task required participants to judge whether a number was greater than 5, pressing the F key for numbers less than 5 and the J key for numbers greater than 5. The number 5 did not appear in this task. The ‘parity’ cue task required participants to judge whether a number was odd or even, pressing the F key for odd numbers and the J key for even ones. The formal experiment consisted of two blocks, with a total of 122 mixed trials. The task requirements were switched randomly between trials, categorizing them into either switch (60 trials) or stay conditions (60 trials). A stay trial was when the task requirement was the same as the previous trial, whereas a switch trial differed from the previous trial. Each trial began with a 500 ms fixation point (“+”), followed by a 200 ms cue stimulus (“size” or “parity”) to remind participants of the current task, then a random blank screen for 300–500 ms. The visual stimulus was presented for 300 ms, followed by a blank response screen for 1500 ms, a random blank screen for 1000–1200 ms, and the next trial. Switch costs were the difference in accuracy between stay and switch trials. Smaller switch costs indicated better switching performance in response to visual stimulation.

2.2.6. Auditory Task-Switching Paradigm

The materials for the auditory task-switching paradigm consisted of the numbers 1–9 spoken in male and female voices. Each auditory stimulus lasted 300 ms and was clear, identifiable, and emotionally neutral. The experimental process was the same as the visual task-switching paradigm.

3. Results

SPSS Version 24.0 was used for the statistical analysis. This study systematically examined the relationship between bilingual experience and executive functions using three main methods: independent samples t-tests, correlation analysis, and multiple regression analysis. These methods aimed to address two key research questions: (a) Is the bilingual effect modality-specific or modality-general? (b) Is the bilingual effect process-specific or process-general?
First, to assess group differences, we conducted analysis of variance (ANOVA). For example, in the Stroop task, response time was analyzed using a two-factor variance ANOVA (2 × 2: conditions: congruent vs. inconsistent, participant type: bilingual vs. monolingual). Similarly, variance analysis was applied to the N-back task (3 × 2: conditions: 1-back, 2-back, 3-back, participant type: bilingual vs. monolingual) and the task-switching paradigm (2 × 2: conditions: stay vs. switch, participant type: bilingual vs. monolingual). The p-values that did not meet the sphericity assumption were corrected using the Greenhouse–Geisser method. The results of t-tests were corrected by the false discovery rate method. However, due to space constraints and the fact that the ANOVA results were not central to our research questions, we chose not to present them in detail. Instead, we focused on reporting the independent sample t-test results, which are the core findings of this study.
Next, correlation analysis was conducted to examine the relationships between bilingual experience and executive functions. Finally, multiple regression analysis was performed to evaluate the predictive power of bilingual experience on executive functions, controlling for potential confounding variables such as age, socioeconomic status (SES), and IQ.

3.1. Differences in EFs Between Bilingual and Monolingual Groups

Independent sample t-tests were used to compare bilingual and monolingual participants on the EF tasks (see Table 2). In terms of inhibitory control, no significant differences were found between the two groups on the visual Stroop task (ts(54) < 1.50, ps > 0.05). However, in the auditory domain, the bilingual group exhibited a significantly smaller Stroop effect compared to the monolingual group.
In terms of working memory, the bilingual group demonstrated significantly higher accuracy (proportion of hits minus proportion of false alarms) on both the visual and auditory tasks in the 2-back and 3-back conditions compared to the monolingual group (see Figure 1). However, the performance of the two groups was similar in the 1-back condition. These findings suggest that bilingual participants may possess superior working memory abilities in both the auditory and visual modalities.
Finally, in terms of cognitive flexibility, no significant differences were found between the two groups in terms of switch costs for both the auditory and visual task-switching paradigms (ts(54) < 1.50, ps > 0.05). These findings suggest that there is no evidence to support the existence of a bilingual effect in cognitive flexibility, either in the visual or auditory modality.

3.2. Correlation Analysis: Bilingualism and Executive Functions

The Pearson correlations presented in Figure 2 reveal potential associations between EF measures and bilingualism, suggesting that language proficiency may indeed be related to certain aspects of EF. Specifically, the results indicate that higher proficiency in the second language (L2) is predictive of improved performance on both auditory and visual working memory updating tasks. However, language proficiency does not appear to be linked with inhibitory control or cognitive flexibility. These findings suggest that the bilingual effect is more likely to manifest in the domain of working memory rather than in other cognitive abilities.

3.3. Multiple Regression Analyses

Both the group differences and correlation analyses did not account for potentially confounding variables that may influence EFs, such as age (Doebel, 2020), socioeconomic status (Hackman & Farah, 2009), and IQ (Hargreaves & Aksentijevic, 2011). To determine whether bilingualism can explain differences in EF task performance between the two groups, we conducted a multivariate multiple regression analysis on the six dependent measures (i.e., the six EF tasks: auditory and visual versions of inhibitory control, working memory, and cognitive flexibility), while accounting for the effects of age, socioeconomic status, and IQ. The results of the regression analysis were consistent with the correlation findings (see Table 3). Specifically, bilingualism can predict performance in both auditory and visual working memory tasks. However, it is not predictive of inhibitory control or cognitive flexibility abilities in either auditory or visual tasks.

4. Discussion

This study systematically explored the relationship between bilingual experience and executive functions (EFs) through matched visual and auditory tasks, aiming to determine whether the bilingual effect is modality-specific or modality-general (Research Question a), and whether it is process-specific or process-general (Research Question b). The correlation results showed a significant relationship between second-language experience and working memory, but no significant relationship was observed with inhibitory control or cognitive flexibility. Similarly, the regression analysis indicated that, after controlling for confounding variables such as intelligence, socioeconomic status, and age, bilingualism predicted performance in both auditory and visual working memory tasks. However, no bilingual advantage was found in inhibitory control or cognitive flexibility.
These findings addressed our first research question by demonstrating that the bilingual effect was modality-general, as it was observed in both auditory and visual working memory tasks. In response to our second research question, the results indicated that the bilingual effect was process-specific, as it was limited to working memory and did not extend to inhibitory control or cognitive flexibility. Thus, our study provided evidence that bilingualism can enhance working memory, but this effect is specific to the process of working memory and applies across modalities (auditory and visual). The following discusses this result from two perspectives.

4.1. Bilingual Experience Predicts Working Memory

Specifically, our research findings indicate that bilingual experience can predict performance in visual and auditory working memory tasks, highlighting advantages for bilingual individuals in both visual and auditory working memory. Previous studies have also reported similar findings (Alain et al., 2018; Dong & Liu, 2016; Monnier et al., 2021). As an illustration, Dong and Liu (2016) conducted a longitudinal study demonstrating a noteworthy enhancement in the visual working memory capability of college students following a semester of interpretation and translation training. Additionally, a comprehensive meta-analysis conducted by Monnier et al. (2021), incorporating findings from 116 independent studies, indicated a modest effect size of 0.12, favoring a higher working memory capacity for bilingual individuals compared to monolinguals.
This result suggests that the dual language experience might have strengthened the working memory capacity of bilinguals (Alain et al., 2018; Antoniou, 2019; Bialystok, 2017). Many cognitive psychologists argue that executive functions, particularly working memory, are not isolated modules, but rather domain-general capacities closely linked to individual experiences (MacDonald & Christiansen, 2002; Schwering & MacDonald, 2020). Therefore, the potential of bilingual experience to enhance working memory can be attributed to its unique intervention characteristics. Previous research has identified several key features for improving working memory: Characteristic (1): Only challenging and progressively difficult training tasks can enhance an individual’s working memory; repetitive or simple task repetition does not contribute to improving working memory (Diamond, 2016; Diamond & Lee, 2011). Characteristic (2): Persistent and consistent training is crucial; the improvement of working memory significantly depends on the duration of the training (Diamond & Lee, 2011; Thorell et al., 2009). It is evident that bilingual experience meets both of these key characteristics. The Bilingual Interactive Activation (BIA) model, proposed by Dijkstra and Van Heuven, posits that a key characteristic of bilingual cognition is the simultaneous activation of both languages (Bialystok, 2017; Bialystok et al., 2016; Dijkstra & Van Heuven, 2002). When bilinguals encounter a stimulus, such as hearing or seeing a word, the lexical representations of both languages are activated, regardless of which language the stimulus originates from (Dijkstra & Van Heuven, 2013; Dijkstra & Van Heuven, 2002). This activation is automatic and non-selective, meaning it occurs without the individual’s intention or conscious control (Dijkstra & Van Heuven, 2013; Dijkstra & Van Heuven, 2002). In order to successfully identify and use the correct language, bilinguals must manage the ongoing competition between both languages. This process undoubtedly demands significant working memory resources. This demand is particularly pronounced in the context of interpreting, where simultaneous interpreters must rapidly convey the speaker’s message while simultaneously processing incoming information (Antoniou, 2019; Bialystok et al., 2012; Diamond, 2013). Secondly, the learning of a second language inherently involves a progression from easy to difficult, following a cyclical and progressively challenging pattern that requires long-term commitment. Therefore, it is reasonable to assume that this training would enhance the working memory of bilingual individuals.
From a neuroscience perspective, the enhancement of working memory in bilinguals may stem from changes in the function and structure of brain regions involved in working memory. Functionally, Alain et al. (2018) utilized functional magnetic resonance imaging (fMRI) in conjunction with the N-back task and found that bilinguals exhibited an advantage in auditory working memory. Specifically, bilinguals showed lower activation in the prefrontal cortex compared to monolinguals, suggesting that bilinguals use neural resources more efficiently, thereby successfully engaging in the working memory task (Alain et al., 2018; Huang et al., 2013). Furthermore, bilinguals may exhibit greater functional connectivity within and across networks relevant to executive control, highlighting the more flexible and efficient coordination between different neural regions and networks facilitated by bilingual experience (Grady et al., 2015). Structurally, bilingual experience has been found to increase gray matter density in regions implicated in executive control, such as the dorsolateral prefrontal cortex (DLPFC), left caudate nucleus (LCN), and anterior cingulate cortex (ACC) (Hayakawa & Marian, 2019; Olulade et al., 2016). These brain regions and networks are crucial for supporting working memory. Therefore, the transfer effects of bilingual experience on working memory may result from changes in the function and structure of these key brain regions. These beneficial changes, in turn, can enhance language learning and other cognitive functions (Hayakawa & Marian, 2019).
Some studies, however, have not observed a working memory advantage in bilinguals (Keijzer, 2013; Ratiu & Azuma, 2014), which may be attributed to the relatively lower difficulty levels of their tasks. According to the characteristics of working memory training research, the training effects on working memory tend to manifest in tasks with moderate difficulty levels, as overly simplistic or overly challenging tasks can lead to ceiling or floor effects, thereby diminishing the training effects on working memory (Diamond, 2013; Diamond et al., 2007). For example, a study employing a straightforward task, with reaction times typically less than 500 ms, did not find evidence of a bilingual effect (Bialystok et al., 2014). This may be attributed to the task’s simplicity, leading to a lack of sufficient sensitivity (Antoniou, 2019; Diamond, 2013). In contrast, bilinguals are more prone to showcase an advantage in tasks of greater complexity. Ma et al. (2020) demonstrated that the advantageous effect of proficient bilinguals was more prominent under conditions of high memory load. Our study also yielded similar results, revealing that bilinguals demonstrated significantly higher accuracy than monolinguals in the 2-back and 3-back conditions. However, no significant difference between the two groups was observed in the 1-back condition, and this effect remained consistent in both visual and auditory tasks. In summary, we posit that under conditions of high memory load, a clear relationship between bilingual experience and working memory capacity becomes evident.

4.2. Weak Relationship Between Bilingual Experience and Inhibitory Control and Cognitive Flexibility

We found that proficiency in a second language was not significantly related to inhibitory control and cognitive flexibility. Moreover, after accounting for relevant confounding variables such as intelligence, socioeconomic status, and age, bilingual experience did not predict performance in auditory and visual inhibitory control and cognitive flexibility tasks. This may suggest that bilinguals do not exhibit advantages in inhibitory control and cognitive flexibility in both visual and auditory modalities. Previous research has also uncovered similar results (Dick et al., 2019; Hilchey & Klein, 2011; Lehtonen et al., 2018). For instance, recent studies have failed to identify a significant difference in visual inhibitory control between bilinguals and monolinguals, indicating the absence of an inhibitory control advantage in bilinguals (Dick et al., 2019; Giguere et al., 2022). Similarly, in a study utilizing event-related potentials (ERPs) to investigate cognitive flexibility, no significant differences were observed between monolinguals and bilinguals in the core ERP components N2 and P3b, indicating the absence of a cognitive flexibility advantage in bilinguals (Lopez Zunini et al., 2019).
Previous research has reported advantages for bilinguals in inhibitory control or cognitive flexibility; however, there may not have been sufficient control for confounding variables related to EFs (Paap et al., 2015). That is, this “bilingual effect” can be attributed to the interference of additional variables. For example, Morton and Harper (2007) (conducted a study using the same task, methodology, and design as Bialystok et al. (2004). However, Morton’s study accounted for the socioeconomic status (SES) balance between bilinguals and monolinguals, while Bialystok’s study did not control for SES (Bialystok et al., 2004; Morton & Harper, 2007). Interestingly, Bialystok reported a bilingual effect, while Morton found a weaker relationship between bilingual experience and inhibitory control (Bialystok et al., 2004; Morton & Harper, 2007). Similarly, a meta-analytics study revealed a minimal bilingual effect for cognitive flexibility, and this advantage disappeared after correcting for bias (Lehtonen et al., 2018). Our study also underscores the importance of controlling for additional variables related to EFs. Initially, we observed a reduced Stroop effect in bilinguals, suggesting a potential advantage in inhibitory control. However, this advantage disappeared once we accounted for additional variables such as age, IQ, and SES. These findings suggest that extra variables associated with EFs may contribute to the observation of a false “bilingual effect”, emphasizing the need for comprehensive control of these variables in experimental settings.

4.3. Limitation

This study has several limitations that should be considered. First, a cross-sectional design was employed, comparing bilinguals and monolinguals, which cannot establish a causal relationship between bilingual experience and executive functions (EFs) and does not fully control for inherent individual differences between the two groups. To address this, we controlled for additional variables influencing EFs, including age, intelligence, and socioeconomic status (SES). Future research could use a longitudinal design to investigate causal links between bilingual experiences and EFs in different sensory modalities. Second, some studies contradict our findings, possibly due to factors such as participants’ age and specific bilingual experiences. Therefore, future research should carefully consider these factors (Degirmenci et al., 2022; Dong & Liu, 2016; Goodrich et al., 2022). Third, this study explored the bilingual effect only at the behavioral level. Future research could utilize techniques such as ERP or fMRI to explore the cognitive neural mechanisms underlying the bilingual effect on EFs, especially in relation to differences between visual and auditory modalities.

5. Conclusions

Most research on bilingual experience and executive functions has focused primarily on the visual domain, leaving uncertainty regarding whether bilingual effects differ across visual and auditory channels. To fill this gap, the present study systematically explored the relationship between bilingual experience and executive functions, specifically examining three subcomponents: inhibitory control, working memory, and cognitive flexibility. We recruited both monolingual Chinese and bilingual Chinese–English participants and designed controlled visual and auditory tasks to assess their executive function performance. This study aimed to answer two key research questions: (a) Is the bilingual effect modality-specific or modality-general? (b) Is the bilingual effect process-specific or process-general? The results showed that, after controlling for variables like intelligence, socioeconomic status, and age, bilingualism significantly predicted performance on both auditory and visual working memory tasks, explaining 34% and 19% of the variance, respectively. However, no evidence was found to support the presence of a bilingual advantage in inhibitory control or cognitive flexibility. In conclusion, the bilingual effect observed in this study was both process-specific and modality-general: it enhanced working memory performance but did not extend to inhibitory control or cognitive flexibility, being evident in both auditory and visual modalities. These findings contribute to a deeper understanding of the bilingual effect on executive functions, offering valuable insights for the design of foreign language education and further research in cognitive development.

Author Contributions

Conceptualization, J.C. and G.L.; methodology and formal analysis, J.C. and Z.X.; data curation J.C. and Z.L.; writing—original draft J.C. and Z.L.; writing—review and editing, J.C. and G.L.; visualization, Z.X.; funding acquisition, G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China, grant number 61472330 and 61872301.

Institutional Review Board Statement

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of School of Electronic and Information Engineering at Southwest University (protocol code CEIE2023031001 and approved on 10 March 2023).

Informed Consent Statement

Informed consent was obtained from all subjects involved in this study.

Data Availability Statement

The data presented in this study are available on request from the corresponding author (the data are not publicly available due to privacy or ethical restrictions).

Acknowledgments

We would like to thank all participants who took part in this study. We thank the National Natural Science Foundation of China for funding the current research.

Conflicts of Interest

The authors declare no conflicts of interest.

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Behavsci 15 00134 g001
Figure 1. Accuracy rate and response time for bilinguals and monolinguals in the visual N-back task (left) and the auditory N-back task (right). ** p < 0.01; *** p < 0.001; n.s. not significant.
Figure 1. Accuracy rate and response time for bilinguals and monolinguals in the visual N-back task (left) and the auditory N-back task (right). ** p < 0.01; *** p < 0.001; n.s. not significant.
Behavsci 15 00134 g001
Behavsci 15 00134 g002
Figure 2. Scatter plots with correlation analysis between the proficiency in the second language and performances in six EF tasks. Stroop interference effect (Stroop task): incongruent minus congruent RTs. Accuracy (N-back task): proportion hits minus proportion false alarms). Switch costs (task-switch paradigms): switch minus stay RTs. ** p < 0.01.
Figure 2. Scatter plots with correlation analysis between the proficiency in the second language and performances in six EF tasks. Stroop interference effect (Stroop task): incongruent minus congruent RTs. Accuracy (N-back task): proportion hits minus proportion false alarms). Switch costs (task-switch paradigms): switch minus stay RTs. ** p < 0.01.
Behavsci 15 00134 g002
Table 1. Demographic and linguistic information of the Chinese monolingual and Chinese–English bilingual participants.
Table 1. Demographic and linguistic information of the Chinese monolingual and Chinese–English bilingual participants.
Bilinguals M (SD)Monolinguals M (SD)
Age20.21 (1.34)19.96 (1.58)
Gender4 males, 24 females5 males, 23 females
SES3.23 (0.40)3.18 (0.39)
Intelligence (out of 12)9.68 (1.66)9.36 (1.37)
L2 AoA5.61 (1.66)7.04 (0.64)
IELTS score (total)7.21 (0.36)--
IELTS score (understanding)7.81 (0.75)--
IELTS score (speaking)6.45 (0.48)--
IELTS score (reading)7.71 (0.64)--
IELTS score (writing)6.50 (0.45)--
Self-reported L2 understanding proficiency
(none: 1–fluent (native): 10)		7.50 (1.30)1.50 (0.69)
Self-reported L2 speaking proficiency
(none: 1–fluent (native): 10)		6.61 (0.96)1.43 (0.79)
Self-reported L2 reading proficiency
(none:1–fluent (native): 10)		7.43 (1.29)1.82 (0.82)
Self-reported L2 writing proficiency
(none: 1–fluent (native): 10)		6.79 (1.13)1.68 (0.86)
L2 use at home
(All L1: 0%–All L2: 100%)		16.07% (20.65%)--
L2 use in non-home situations (school)
(All L1: 0%–All L2: 100%)		41.07% (18.28%)--
Notes: SES: socioeconomic status; AoA: age of acquisition; L2: second language (English); and self-rated proficiency rated on a 10-point scale, where 1 is no ability at all, and 10 is fluent (native) ability. Language use was rated on a 5-point scale: 0%, 25%, 50%, 75%, and 100% of the time. Age of acquisition was reported for monolingual speakers because many received English instruction at school but never achieved fluency.
Table 2. Mean scores (M) and standard deviations (SD) of EFs measures in bilinguals and monolinguals.
Table 2. Mean scores (M) and standard deviations (SD) of EFs measures in bilinguals and monolinguals.
EFs MeasuresBilinguals
M (SD)		Monolinguals
M (SD)		p-Values
Inhibitory Control (response time in ms)
 Visual Stroop
 Congruent646 (72)614 (76)0.22
 Incongruent703 (75)689 (89)0.53
   Difference (Stroop effect)58 (45)76 (71)0.26
 Auditory Stroop
 Congruent610 (57)639 (75)0.10
 Incongruent648 (66)696 (86)0.03
   Difference (Stroop effect)39 (32)56 (33)0.05
Working Memory (accuracy: proportion of hits minus proportion of false alarms)
 Visual N-back
 1-back0.88 (0.09)0.84 (0.09)0.10
 2-back0.78 (0.11)0.67 (0.14)0.001
 3-back0.63 (0.16)0.47 (0.15)<0.001
   Combined0.76 (0.12)0.66 (0.11)0.001
 Auditory N-back
 1-back0.89 (0.06)0.86 (0.08)0.06
 2-back0.78 (0.11)0.69 (0.13)0.01
 3-back0.63 (0.16)0.47 (0.16)<0.001
   Combined0.77 (0.10)0.67 (0.11)0.001
Cognitive Flexibility (response time in ms)
 Visual Task-switching
 Stay813 (118)824 (109)0.71
 Switch864 (122)881 (112)0.71
   Difference (Switch costs)51 (32)56 (49)0.62
 Auditory Task-switching
 Stay861 (98)952 (79)<0.001
 Switch919 (128)1036 (79)<0.001
   Difference (Switch costs)57 (48)84 (66)0.09
Table 3. Summary of univariate regression analyses.
Table 3. Summary of univariate regression analyses.
PredictorsInhibitory Control (incongruent minus congruent RTs)
VisualAuditory
βtβt
Age−0.14−0.830.211.34
SES0.251.77−0.06−0.42
IQ0.020.11−0.19−1.28
Bilingualism−0.16−1.19−0.26−1.94
R 2 /adj. R 2 0.08/0.01 0.11/0.04
PredictorsWorking Memory (proportion hits minus proportion false alarms)
Visual Auditory
βtβt
Age0.110.84−0.02−0.16
SES−0.04−0.310.080.62
IQ0.423.32 **0.241.77
Bilingualism0.373.35 **0.393.20 **
R 2 /adj. R 2 0.39/0.34 0.25/0.19
PredictorsCognitive Flexibility (switch minus stay RTs)
Visual Auditory
βtβt
Age−0.13−0.820.030.22
SES−0.15−1.06−0.05−0.30
IQ0.020.13−0.11−0.75
Bilingualism−0.05−0.35−0.22−1.60
R 2 /adj. R 2 0.06/−0.02 0.07/−0.01
Bilingualism: 1 = bilingual participants; −1 = monolingual participants. ** p < 0.01.
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Chen, J.; Li, Z.; Xiong, Z.; Liu, G. Working Memory as the Focus of the Bilingual Effect in Executive Functions. Behav. Sci. 2025, 15, 134. https://doi.org/10.3390/bs15020134

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Chen J, Li Z, Xiong Z, Liu G. Working Memory as the Focus of the Bilingual Effect in Executive Functions. Behavioral Sciences. 2025; 15(2):134. https://doi.org/10.3390/bs15020134

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Chen, Jiejia, Zitong Li, Zhiheng Xiong, and Guangyuan Liu. 2025. "Working Memory as the Focus of the Bilingual Effect in Executive Functions" Behavioral Sciences 15, no. 2: 134. https://doi.org/10.3390/bs15020134

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Chen, J., Li, Z., Xiong, Z., & Liu, G. (2025). Working Memory as the Focus of the Bilingual Effect in Executive Functions. Behavioral Sciences, 15(2), 134. https://doi.org/10.3390/bs15020134

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