The past decade has witnessed some dramatic methodological changes in the wider disciplines of psycholinguistics, psychology, and experimental linguistics. One such set of changes comprises the development of open and transparent research practices, which have increasingly been adopted in response to concerns that empirical results often fail to replicate and may not generalise across samples and experimental conditions (Gibson & Fedorenko, 2013; Maxwell, Lau, & Howard, 2015; McElreath & Smaldino, 2015; Yarkoni, 2020). Another important set of changes concerns the use of sophisticated statistical techniques, such as mixed-effects models (Baayen, Davidson, & Bates, 2008) and Bayesian analyses (Vasishth, Nicenboim, Beckman, Li & Kong, 2018), which can provide much more information about magnitudes of effects and sources of variation than the more traditional statistical approaches.

The extent to which findings in bilingualism research are contingent on specific analytic choices, experimental designs, or operationalisations, is currently unknown. Poor availability of data, analysis code, and materials has hindered the development of cumulative lines of research. In this review, we survey current practices and advocate a credibility revolution in bilingualism research through the adoption of minimum standards of transparency. Full disclosure of data and code is necessary not only to assess the reproducibility of original findings, but also to test the robustness of these findings to different analytic specifications. Similarly, full provision of experimental materials and protocols underpins assessment of both the replicability of original findings, as well as their generalisability to different contexts and samples. We illustrate the review with examples where good practice has advanced the agenda in bilingualism research and highlight resources to help researchers get started.

Preregistration is an open science practice that requires the specification of research hypotheses and analysis plans before the data are inspected. Here, we discuss the benefits of preregistration for hypothesis-driven, confirmatory bilingualism research. Using examples from psycholinguistics and bilingualism, we illustrate how non-peer reviewed preregistrations can serve to implement a clean distinction between hypothesis testing and data exploration. This distinction helps researchers avoid casting post-hoc hypotheses and analyses as confirmatory ones. We argue that, in keeping with current best practices in the experimental sciences, preregistration, along with sharing data and code, should be an integral part of hypothesis-driven bilingualism research.

Low power in empirical studies can be compared to blurred vision. It makes the signal ambiguous, so that conclusions depend more on interpretation than on observation. Data patterns that look sensible are published as evidence for theoretical positions and unclear patterns are discarded as noise, whereas both could be due to sampling error or could be a perfect reflection of the population parameters. Simulations indicate that little research with sample sizes lower than 100 participants per group provides a picture of enough resolution to draw firm conclusions. This is particularly true for research comparing groups of people and involving interaction effects. As a result, it is to be feared that many findings in bilingualism research do not have a firm base, certainly not if they go beyond a simple comparison of two within-participants conditions.

Meta-analysis overcomes a number of the limitations of traditional literature reviews (Norris & Ortega, 2006). Consequently, the use of meta-analysis as a synthetic technique has been applied across a range of scientific disciplines in recent decades. This paper seeks to formally introduce the potential of meta-analysis to the field of bilingualism. In doing so, we first describe a number of advantages to the meta-analytic approach such as greater systematicity, objectivity, and transparency relative to narrative reviews. We also outline the major stages in conducting a meta-analysis, highlighting critical considerations encountered at each stage. These include (a) domain definition, (b) coding scheme development and implementation, (c) analysis, and (d) interpretation. The focus, however, is on providing a conceptual introduction rather than a full-length tutorial. Meta-analyses in bilingualism and nearby fields are referred to throughout in order to illustrate the points being made.

This paper introduces the generalized additive mixed model (GAMM) and the quantile generalized additive mixed model (QGAMM) through reanalyses of bilinguals’ lexical decision data from Dijkstra et al. (2010) and Miwa et al. (2014). We illustrate how regression splines can be used to test for nonlinear effects of cross-language similarity in form as well as for controlling experimental trial effects. We further illustrate the tensor product smooth for a nonlinear interaction between cross-language semantic similarity and word frequency. Finally, we show how the QGAMM helps clarify whether the effect of a particular predictor is constant across distributions of RTs.

Much work has shown that differences in the timecourse of language processing are central to comparing native (L1) and non-native (L2) speakers. However, estimating the onset of experimental effects in timecourse data presents several statistical problems including multiple comparisons and autocorrelation. We compare several approaches to tackling these problems and illustrate them using an L1-L2 visual world eye-tracking dataset. We then present a bootstrapping procedure that allows not only estimation of an effect onset, but also of a temporal confidence interval around this divergence point. We describe how divergence points can be used to demonstrate timecourse differences between speaker groups or between experimental manipulations, two important issues in evaluating L2 processing accounts. We discuss possible extensions of the bootstrapping procedure, including determining divergence points for individual speakers and correlating them with individual factors like L2 exposure and proficiency. Data and an analysis tutorial are available at https://osf.io/exbmk/.

Research in bilingualism often involves quantifying constructs of interest by the use of rating scales: for example, to measure language proficiency, dominance, or sentence acceptability. However, ratings are a type of ordinal data, which violates the assumptions of the statistical methods that are commonly used to analyse them. As a result, the validity of ratings is compromised and the ensuing statistical inferences can be seriously distorted. In this article, we describe the problem in detail and demonstrate its pervasiveness in bilingualism research. We then provide examples of how bilingualism researchers can employ an appropriate solution using Bayesian ordinal models. These models respect the inherent discreteness of ratings, easily accommodate non-normality, and allow modelling unequal psychological distances between response categories. As a result, they can provide more valid, accurate, and informative inferences about graded constructs such as language proficiency. Data and code are publicly available in an OSF repository at https://osf.io/grs8x.

Bilingual speakers are less accurate and slower than monolinguals in word production. This bilingual cost has been demonstrated primarily for nouns. This study compared verb and noun retrieval to better understand bilingual lexical representation and test alternate hypotheses about bilingual cost. Picture naming speeds from highly proficient English–Spanish bilinguals showed a smaller bilingual cost for verbs compared to nouns. In Experiment 1, picture naming speeds were influenced by name agreement, age-of-acquisition and word length. Additionally, noun (but not verb) naming speed was predicted by word frequency. Experiment 2 examined two potential explanations for the smaller bilingual cost for verbs: verbs experience weaker cross-language interference (measured by translation speed) and smaller frequency effects. Both these predictions were confirmed, showing crucial differences between verbs and nouns and suggesting that cross-language facilitation rather than interference influences bilingual lexical retrieval, and that the frequency lag account of bilingual cost is more applicable to nouns than to verbs. We propose a Bilingual Integrated Grammatical Category model for highly proficient bilinguals to represent lexical category differences.

First-language research suggests that new words, after initial episodic-memory encoding, are consolidated and hence become lexically integrated. We asked here if lexical consolidation, about word forms and meanings, occurs in a second language. Italian–English sequential bilinguals learned novel English-like words (e.g., apricon, taught to mean “stapler”). fMRI analyses failed to reveal a predicted shift, after consolidation time, from hippocampal to temporal neocortical activity. In a pause-detection task, responses to existing phonological competitors of learned words (e.g., apricot for apricon) were slowed down if the words had been learned two days earlier (i.e., after consolidation time) but not if they had been learned the same day. In a lexical-decision task, new words primed responses to semantically-related existing words (e.g., apricon-paper) whether the words were learned that day or two days earlier. Consolidation appears to support integration of words into the bilingual lexicon, possibly more rapidly for meanings than for forms.

Four hypotheses regarding the impact of discourse context on cross-language lexical activation were tested. Highly-proficient, Spanish–English bilinguals read all-English paragraphs containing non-identical and identical cognates or noncognate controls while their eye-movements were tracked. There were four paragraph conditions based on a full crossing of semantic bias from the topic sentence and sentence containing the critical word. In analyses in which cognate status was treated categorically there was an interaction between global bias and cognates status such that the observed inhibitory effects of cognate status were attenuated in global-neutral contexts. Follow-up analyses on the non-identical cognates in which orthographic overlap was treated continuously revealed a U-shaped function between orthographic overlap and processing time, which was more pronounced in global-neutral contexts. The overall pattern of findings is consistent with a combined operation of resonant-based and feature-restriction mechanisms of context effects.

The grain size of orthographic representations prompted by a consistent orthography (like Spanish or Basque) increases if reading is simultaneously learned in another language with an inconsistent orthography (like French). Here, we aimed to identify item properties that trigger this grain-size accommodation in bilingual reading. Twenty-five French–Basque and 25 Spanish–Basque bilingual children attending Grade 3 read Basque words and pseudowords containing “complex” letter clusters mapping to one sound in French but several sounds in Basque or Spanish, and “simple” letter clusters mapping to the same sound structure in all three languages. Only French speaking children read “complex” Basque words faster than “simple” ones, suggesting that they accessed multi-letter “French” units to boost lexical processing. A negative complexity effect was found for pseudowords across groups. We discuss the existence of flexible cross-linguistic transfer in bilingual reading, proposing that the grain size of orthographic representations adjusts to item-specific characteristics during reading.

Bilinguals’ two languages seem to be coactivated in parallel during reading, speaking, and listening. However, this coactivation in writing has been scarcely studied. This study aimed to assess orthographic coactivation during spelling-to-dictation. We took advantage of the presence of polyvalent graphemes in Spanish (one phonological representation with two orthographic specifications, e.g., / b /for both the graphemes v and b) to manipulate orthographic congruency. Spanish–English bilinguals were presented with cross-linguistic congruent (movement–movimiento) and incongruent words (government–gobierno) for a dictation task. The time and accuracy to initiate writing and to type the rest-of-word (lexical and sublexical processing) were recorded in both the native language (L1) and the second language (L2). Results revealed no differences between conditions in monolinguals. Bilinguals showed a congruency and language interaction with better performance for congruent stimuli, which was evident from the beginning of typing in L2. Language coactivation and lexical–sublexical interaction during bilinguals’ writing are discussed.

Mentalizing, a dynamic form of social cognition, is strengthened by language experience. Past research has found that bilingual children and adults outperform monolinguals on mentalizing tasks. However, bilingual experiences are multidimensional and diverse, and it is unclear how continuous individual differences in bilingual language experience relate to mentalizing. Here, we examine whether individual differences in bilingual language diversity, measured through language entropy, continuously pattern with mentalizing judgments among bilingual adults, and whether this relationship is constrained by first vs. second language reading. We tested sixty-one bilingual adults on a reading and inference task that compared mental state and logical inferences. We found that greater language diversity patterned with higher mentalizing judgments of mental state inferences across all readers, and that L2 readers attributed more mentalizing to logical inferences compared to L1 readers. Together, we found evidence of a positive relationship between continuous individual differences in bilingual language diversity and mentalizing.

We investigated conceptual representations for translation word pairs in bilinguals who learned their languages in different cultural contexts. Mandarin–English bilinguals were presented with a word, and then a picture, and decided if they matched. Both behavioural and ERP data were collected. In one session, words were in English and in another they were the Mandarin translations. Critical pictures matched the prior word and were either biased to Chinese or Canadian culture. There was an interaction of test language and picture type in RT and errors in the behavioural data, and in five components in the ERP data, indicating that the task was easier when the culture depicted in the picture was congruent with the language of the preceding word. These findings provide evidence that the specific perceptual experiences that bilinguals encounter when learning words in each language have an impact on the semantic features that are activated by those words.