The bilingual-advantage hypothesis — that managing two languages improves domain-general executive functions such as inhibitory control, monitoring, and task switching — dominated bilingualism research for decades before losing consensus. A 2017 bibliometric study documented that publications challenging the behavioral advantage (CBA) rose sharply in 2014–2015 while publications supporting it (SBA) stagnated, and asked what this shift means: a true decline in empirical effect sizes, reduced publication bias against challenging results, the novelty of the challenging findings, or shifting researcher interests demanding a change of paradigm. This problem asks for a defensible account of the status of the bilingual executive-control advantage and of the post-2013 publication shift. Meta-analytic work since 2018 has largely settled the adult aggregate-effect question (near-zero after publication-bias correction) and points the same way for children, yet sign-count analyses reach the opposite conclusion, no study has determined the causes of the publication shift, the category-proportion follow-up beyond June 2016 has not been performed, and the methodological moderators driving disagreement remain unidentified. These surviving components constitute the open core.

Background

The bilingual-advantage (BA) hypothesis is the claim that people who regularly manage two languages (bilinguals) outperform monolinguals on executive functions — the domain-general processes controlling attention and behavior, including inhibitory control (suppressing irrelevant responses), cognitive/attentional monitoring, task switching, and working memory. Building on research from the 1980s onward, the hypothesis became one of the most influential and heavily studied claims in the psychology of bilingualism, and it feeds public arguments about bilingual education and cognitive aging. Beginning in the late 2000s the evidence fractured: Morton and Harper (2007) showed that an early, widely cited advantage on the Simon task (a conflict task requiring response inhibition) disappeared when socioeconomic status was controlled, and Paap and Greenberg (2013), testing young adults across several executive-control paradigms, reported no coherent advantage. de Bruin, Treccani, and Della Sala (2015) then documented publication bias directly: among conference abstracts on bilingualism and executive control from 1999–2012, studies fully supporting the advantage were the most likely to appear as journal articles, and studies challenging it the least. Sanchez-Azanza, López-Penadés, Buil-Legaz, Aguilar-Mediavilla, and Adrover-Roig (2017) added bibliometric evidence: of 139 articles published 2005–2015, classified from their abstracts as supporting (SBA), ambiguous (ABA), not mentioning (NMA), or challenging (CBA) the behavioral advantage, CBA publications rose sharply in 2014–2015 while SBA growth stayed flat, and from 2014 onward a new paper was roughly one and a half times more likely to fall in the CBA category (logistic regression); journal impact factors (a journal-level citation metric) and accumulated citations were otherwise equivalent across categories. Because bibliometric patterns cannot decide between candidate explanations — a decline effect (the tendency for an initially overestimated effect to shrink as replications accumulate), reduced publication bias against null results (challenging results were already available but were unlikely to be published under the previous literature framework), the novelty of the challenging results, or shifting researcher interests demanding a change of paradigm — the authors left open what the shift means, whether empirical effect sizes have systematically declined, whether the shift would persist beyond their June 2016 cut-off, and which methodological moderators (task variance, sample matching on socioeconomic status, convergent validity across tasks — whether different tasks intended to measure the same executive function actually agree) explain why supporting and challenging studies disagree. They called for formal meta-analysis and a mid-term bibliometric follow-up, and in their limitations acknowledged that abstract-only classification might be a source of confirmation bias while defending their classification criteria. Later work has transformed this landscape. Lehtonen et al. (2018) meta-analyzed 152 adult studies (891 effect sizes, including unpublished data): very small advantages in inhibition, shifting, and working memory before correcting for publication bias, and no advantage remaining after correction. For children, Dick et al. (2019) found no bilingual executive-function advantage in the nationally representative ABCD (Adolescent Brain Cognitive Development) sample of 4,524 nine- to ten-year-olds; Gunnerud et al. (2020) found only a marginal overall effect (Hedges' g = 0.06, where Hedges' g is a standardized mean-difference effect-size measure) with publication-bias indications and large unexplained heterogeneity; and Lowe et al. (2021) found g = 0.08 overall, indistinguishable from zero (g = −0.04) after publication-bias adjustment. Against this, Grundy (2020) re-analyzed 167 studies with a Bayesian sign-count approach — asking on how many comparisons bilinguals numerically outperform monolinguals, rather than averaging effect sizes — and found performance favors bilinguals far more often than chance, a result he showed was not explained by publication bias, year of publication, or sample size, reframing the question as when, rather than whether, bilinguals outperform. Yurtsever, Anderson, and Grundy (2023) extended this sign-count logic to children with the same qualitative conclusion, keeping the dispute alive. Van den Noort et al. (2019), reviewing studies to October 2018, reported that a majority of new original studies still found beneficial effects and attributed the persistent disagreement to design factors, while a comprehensive 50-year bibliometric follow-up by Privitera et al. (2026), covering 764 published and unpublished documents, maps the field's trajectory from early universal-advantage claims through empirical reconsideration toward experience-sensitive frameworks, but does not replicate the original SBA/CBA category proportions. The interpretive question posed in 2017 is therefore only partially answered: the aggregate adult effect-size question is largely settled, while the causes of the publication shift, the reconciliation of sign-count and effect-size evidence, the category-proportion follow-up, and the identification of moderators remain open.

Problem Statement

Determine what the post-2013 shift toward challenging findings means for the bilingual executive-control advantage — that is, establish whether, when, and why bilingualism modifies executive control, and whether the literature's trajectory reflects genuine scientific self-correction or changing publication practices. The overarching objective jointly requires the following linked results, only partially delivered by later work: (i) a meta-analytic synthesis of behavioral bilingual-versus-monolingual effect sizes on executive-control tasks across age groups, including unpublished data and explicit publication-bias correction, establishing whether the aggregate advantage is real (the adult case is largely settled at near-zero after correction; the child case remains contested); (ii) a test of whether empirical effect sizes declined over time (a decline effect, with publication year as a moderator) or were instead inflated in early work by publication bias, together with a reconciliation of the divergent conclusions of effect-size meta-analyses and sign-count analyses; (iii) an evidence-based account of the causes of the publication shift, weighing each of the candidate explanations raised by the source — a true decline in effect sizes (a decline effect), reduced publication bias against null results (challenging results were already available but were unlikely to be published under the previous literature framework), the novelty of the challenging results, and shifting researcher interests demanding a change of paradigm; (iv) a follow-up of the publication trend beyond June 2016 in the original supporting/ambiguous/challenging classification, deciding between the source's three scenarios (return to earlier proportions, continued dominance of challenging findings, or balanced coexistence); and (v) identification of the methodological moderators, considering each of the following four candidate families — participant selection and socioeconomic matching, task properties and convergent validity across tasks, sample size, and bilingualism measurement — and stating, with support, whether each explains why supporting and challenging studies disagree.

References

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