The question of how much language a child can learn by modelling the patterns she is exposed to in the environment represents an age-old and persistent controversy in language-acquisition research. On a number of occasions researchers felt confident enough to claim that the controversy had been resolved, in favour of their own viewpoint, of course. One such attempt was Skinner's (1957) behaviourist view of language development, which gave a prominent if not exclusive role to input and experience. After Chomsky's (1959) landmark review, however, Skinner's account was left in pieces and was not further pursued by many. A more recent attempt comes from usage-based accounts according to which children directly build linguistic categories and rules from the language they hear around them. Some believe that these accounts have resolved the controversy for good and have ‘overturned’ alternative less experience-driven approaches (e.g., Ibbotson & Tomasello, 2016; Dabrowska, 2015). Yet, casual inspection of recent research articles reveals that this announcement may be somewhat premature; see, for example, Everaert, Huybregts, Chomsky, Berwick and Bolhuis (2015), Boxell's (2016) rebuttal of Dabrowska (2015), and many acquisition studies published in the journal Language Acquisition.

A growing literature on bilingual development explores relationships between language exposure and learning outcomes. Vocabulary size and pace of grammar learning have been claimed to be causally related to amounts or types of exposure to each language. Strong claims are made about the role of exposure on bilingual outcomes. Some researchers posit a unique learning result: a ‘weak language’. In a critical review, I voice reasons for scepticism that quantity or quality of exposure alone will explain findings. Central constructs are not well defined; inappropriate research methods have been used; the right kind of data is not discussed. Crucially, authors prevaricate on the notion of language itself, switching between cognitive and environmental perspectives. Both are needed to interpret bilingual behaviours but play different roles in the construction of learner grammars.

In an ongoing debate, bilingual research currently discusses whether bilingualism enhances non-linguistic executive control. The goal of this study was to investigate the influence of language-switching experience, rather than language proficiency, on this bilingual executive control advantage. We compared the performance of unbalanced bilinguals, balanced non-switching, and balanced switching bilinguals on two executive control tasks, i.e. a flanker and a Simon task. We found that the balanced switching bilinguals outperformed both other groups in terms of executive control performance, whereas the unbalanced and balanced non-switching bilinguals did not differ. These findings indicate that language-switching experience, rather than high second-language proficiency, is the key determinant of the bilingual advantage in cognitive control processes related to interference resolution.

Idiom priming effects (faster processing compared to novel phrases) are generally robust in native speakers but not non-native speakers. This leads to the question of how idioms and other multiword units are represented and accessed in a first (L1) and second language (L2). We address this by investigating the processing of translated Chinese idioms to determine whether known L1 combinations show idiom priming effects in non-native speakers when encountered in the L2. In two eye-tracking experiments we compared reading times for idioms vs. control phrases (Experiment 1) and for figurative vs. literal uses of idioms (Experiment 2). Native speakers of Chinese showed recognition of the L1 form in the L2, but figurative meanings were read more slowly than literal meanings, suggesting that the non-compositional nature of idioms makes them problematic in a non-native language. We discuss the results as they relate to crosslinguistic priming at the multiword level.

Although international students experience lower attainment at university than home students (Morrison et al., 2005), reasons are poorly understood. Some question the role of language proficiency as international students come with required language qualifications. This study investigated language and literacy of international students who successfully met language entry requirements and those of home students, matched on non-verbal cognition, studying in their native language. In a sample of 63 Chinese and 64 British students at a UK university, large and significant group differences were found at entry and eight months later. Furthermore, language and literacy indicators explained 51% of variance in the Chinese group's grades, without predicting the home students’ achievement. Thus language proficiency appears predictive of academic outcomes only before a certain threshold is reached, and this threshold does not correspond to the minimum language entry requirements. This highlights a systematic disadvantage with which many international students pursue their education.

Previous studies have shown bilingually and monolingually developing children to differ in their sensitivity to referential pragmatic deixis in challenging tasks, with bilinguals exhibiting a higher sensitivity. The learning of adjectives is particularly challenging, but has rarely been investigated in bilingual children. In the present study we presented a pragmatic cue supporting the learning of novel adjectives to 32 Spanish–German bilingual and 28 German monolingual 5-year-olds. The children's responses to a descriptive hand gesture highlighting an object's property were measured behaviorally using a forced choice task and neurophysiologically through functional Near-Infrared Spectroscopy (fNIRS). While no group differences emerged on the behavioral level, fNIRS revealed a higher activation in bilingual than monolingual children in the vicinity of the posterior part of the right superior temporal sulcus (STS). This result supports the prominent role of the STS in processing pragmatic gestures and suggests heightened pragmatic sensitivity for bilingual children.

A growing body of research has investigated bilingual sentence processing. How to account for differences in native (L1) and non-native (L2) processing is controversial. Some explain L1/L2 differences in terms of different parsing mechanisms, and the hypothesis that L2 learners adopt ‘shallow’ parsing has received considerable attention. Others assume L1/L2 processing is similar, and explain L1/L2 differences in terms of capacity-based limitations being exceeded during L2 processing. More generally, the role that working memory plays in language acquisition and processing has garnered increasing interest. Based on research investigating L2 sentence processing, I claim that a primary source of L1/L2 differences lies in the ability to retrieve information constructed during sentence processing from memory. In contrast to describing L1/L2 differences in terms of shallow parsing or capacity limitations, I argue that L2 speakers are more susceptible to retrieval interference when successful comprehension requires access to information from memory.

Speaking more than one language demands a language control system that allows bilinguals to correctly use the intended language adjusting for possible interference from the non-target language. Understanding how the brain orchestrates the control of language has been a major focus of neuroimaging research on bilingualism and was central to our original neurocognitive language control model (Abutalebi & Green, 2007). We updated the network of language control (Green & Abutalebi, 2013) and here review the many new exciting findings based on functional and structural data that substantiate its core components. We discuss the language control network within the framework of the adaptive control hypothesis (Green & Abutalebi, 2013) that predicts adaptive changes specific to the control demands of the interactional contexts of language use. Adapting to such demands leads, we propose, to a neural reserve in the human brain.

Recent theories propose that language-switching in bilinguals influences executive control. We investigated whether switching behaviour, shaped by the bilingual's interactional context as well as personal preferences impacted attentional control. We compared four groups – (i) Edinburgh monolinguals, (ii) Edinburgh non-switching late bilinguals, (iii) Edinburgh non-switching early bilinguals, and (iv) Singapore switching early bilinguals – on two tasks of attentional control. Effects of interactional context were observed, with Singapore bilinguals performing better on conflict resolution in the Attention Network Task and Edinburgh late bilinguals on attentional switching in the Elevator reversal (Test of Everyday Attention) subtest. Our results suggest that the interactional context of bilinguals could impact attentional control differently.

The hypothesis that children surpass adults in long-term second-language proficiency is accepted as evidence for a critical period for language. However, the scope and nature of a critical period for language has been the subject of considerable debate. The controversy centers on whether the age-related decline in ultimate second-language proficiency is evidence for a critical period or something else. Here we argue that age-onset effects for first vs. second language outcome are largely different. We show this by examining psycholinguistic studies of ultimate attainment in L2 vs. L1 learners, longitudinal studies of adolescent L1 acquisition, and neurolinguistic studies of late L2 and L1 learners. This research indicates that L1 acquisition arises from post-natal brain development interacting with environmental linguistic experience. By contrast, L2 learning after early childhood is scaffolded by prior childhood L1 acquisition, both linguistically and neurally, making it a less clear test of the critical period for language.