According to usage-based approaches to language acquisition, linguistic constructions should display prototype effects, or graded category membership (e.g., Bybee, 2010). Using the prototype-plus-distortion methodology (Franks & Bransford, 1971), Ibbotson, Theakston, Lieven, and Tomasello (2012) have provided evidence for prototype effects in adult native English speakers, who had false-positive recognition of sentences with prototypical transitive semantics as having been previously encountered after being exposed to non-prototypical transitive semantics. In the current study, I adopted this methodology and investigated whether the effects can be replicated and additionally observed from English-as-a-second-language (ESL) learners. Results from two groups of adult native English speakers (N=20 and N=21), each exposed to a different stimuli set, suggested some, but not strong, effects and revealed the complexity of the use of this methodology with linguistic materials. Moreover, no effects were observed from advanced adult ESL learners (N=22), suggesting possible differences between first and second transitive semantic representations.

Mayberry and Kluender (2017) make an important contribution to our understanding of the CPL, reporting the striking differences in regions of brain activation in Martin, a deaf man with very late exposure to an L1, compared to other deaf individuals, when processing single signs of ASL. They conclude: “The unique effects of AoA . . . suggest that the hierarchical structure of language and the architecture of the brain language processing system arise from their interaction over the course of early childhood when brain maturation and language acquisition are temporally synchronized.”

This study newly investigates whether the functional weight of a prosodic cue in the native language predicts listeners’ learning and use of that cue in second-language speech segmentation. It compares English and Dutch listeners’ use of fundamental-frequency (F0) rise as a cue to word-final boundaries in French. F0 rise signals word-initial boundaries in English and Dutch, but has a weaker functional weight in English than Dutch because it is more strongly correlated with vowel quality in English than Dutch. English- and Dutch-speaking learners of French matched in French proficiency and experience, and native French listeners completed a visual-world eye-tracking experiment in French where they monitored words ending with/out an F0 rise (replication of Tremblay, Broersma, Coughlin & Choi, 2016). Dutch listeners made earlier/greater use of the F0 rise than English listeners, and in one condition they made greater use of F0 rise than French listeners, extending the cue-weighting theory to speech segmentation.

We thank the commentators for their thoughtful critiques, which we found both insightful and stimulating to our own thinking. Our first response is that, while debates about the CPL in theoretical contexts are important, the vigor and intensity of these debates should not overshadow the fact that the main goal of our article was to highlight a finding of vital importance: Sufficient language input in early childhood matters deeply because it has long-term consequences (Lillo-Martin, 2018). Woll sums up this point both succinctly and poignantly in her report of a similar case of very late L1 exposure in adulthood who had decades of experience: “For a [deaf] child who, even in the context of early intervention, does not acquire a spoken language, the danger is that they will never have native-like mastery of any L1.” This is what truly matters. Our hope is that our keynote article and the accompanying commentaries might have a positive effect on clinical practice, educational policy, and even parental choice in this regard. In what follows, we discuss the main issues arising from the commentaries. First we note the points of agreement followed by a clarification of what we did not claim in our article. Researchers continue to debate what the shape of the AoA function looks like and its theoretical implications, which we address third. We then address the issues raised as to whether late L1 acquisition and late L2 learning differ in degree or kind, and last we discuss what we mean when we say that language acquisition during post-natal brain growth creates the capacity to learn language.

This study extends research on morphological processing in late bilinguals to a rarely examined language type, Semitic, by reporting results from a masked-priming experiment with 58 non-native, advanced, second-language (L2) speakers of Hebrew in comparison with native (L1) speakers. We took advantage of a case of ‘pure morphology’ in Hebrew, the so-called binyanim, which represent (essentially arbitrary) morphological classes for verbs. Our results revealed a non-native priming pattern for the L2 group, with root-priming effects restricted to non-finite prime words irrespective of binyanim type. We conclude that root extraction in L2 Hebrew word recognition is less sensitive to both morphological and morphosyntactic cues than in the L1, in line with the Shallow-Structure Hypothesis of L2 processing.

Ikizer and Ramirez-Esparza (2017) reported a study suggesting that bilingualism may have a positive impact on people's social skills. They found that a) bilinguals scored higher on a scale that is supposed to reveal social flexibility, and that b) they also report having social interactions more frequently than monolinguals. The authors relate this advantage in social flexibility to the need of exercising language switching in bilingual speakers. In this commentary, we argue that their arguments are not theoretically sound and that their observations are not compelling enough to reach this conclusion.

Is bilingualism better than monolingualism? Previous work shows that bilinguals have an advantage over monolinguals in cognitive flexibility, the ability to shift between different mental sets. In this study, we explore if bilingualism also provides an advantage in social flexibility, which we define as the ability to (a) switch with ease and adapt between different social environments and (b) accurately read social cues in the environment. Data was collected from 465 monolinguals and 206 bilinguals. Bilinguals reported higher social flexibility than monolinguals. Mediation analyses demonstrated that bilinguals’ social flexibility gave them an advantage over monolinguals in the self-reported frequency of social interactions. This study reports the first evidence of a social flexibility advantage of bilinguals, and it suggests that as bilinguals alternate between two languages, they might also alternate between two cultural worlds, providing tools to adapt to different social environments and facilitating the frequency of social interactions.

It has been suggested that bilinguals learn additional languages ‘better’ than monolinguals. However, evidence is sparse, particularly for grammar. We examined behavioral and neural correlates of learning an additional (artificial) language in early Mandarin–English bilinguals, compared to English monolinguals. Following grammar instruction, participants practiced comprehension and production, and judged grammaticality at low and high proficiency while event-related potentials (ERPs) were acquired. Bilinguals and monolinguals did not differ on behavioral measures, but showed distinct ERP patterns. At low proficiency only bilinguals showed a P600, a common ERP correlate of syntactic processing in native speakers of languages. At high proficiency both groups showed P600s, though the monolinguals also evidenced an anterior positivity not typically found in native speakers of languages during syntactic processing. These findings suggest that, even without bilingual/monolingual behavioral differences, bilinguals show ERP patterns for an additional language that are more similar to those of native speakers of languages.

DTI is an established method to study cerebral white-matter microstructure. Two established measures of DTI are fractional anisotropy (FA) and mean diffusivity (MD) and both differ for bilingual and monolingual speakers. Less is known about differences in two other measures called radial (RD) and axial diffusivity (AD). We report differences in mean RD and AD-values in the right superior longitudinal fasciculus (SLF) and forceps minor between bilingual (Hindi–English) and monolingual (English) speakers as well as differences in mean FA-values in the anterior thalamic radiation, right inferior fronto-occipital and inferior longitudinal fasciculus (ILF) and mean MD-values in forceps minor and bilateral SLF. Noteworthy, a positive correlation between L2 proficiency and mean RD-values in the right SLF was observed. We suggest that changes in the geometry of white matter tracts reflect regular bilingual language experience and contend that neuroplasticity in right SLF results from demands on cognitive control for bilingual speakers.

The present study explores whether age of onset of exposure to the second language affects interference resolution at the grammatical gender level and whether cognitive functions contribute to interference resolution. Early and late successive Serbian–Greek bilinguals living in the second language context, along with monolinguals, performed a picture-word interference naming task in a single-language context and a non-verbal inhibition task. We found that gender interference from the first language was only present in late successive bilinguals. Early bilinguals exhibited no interference from the grammatical gender of their mother tongue and showed more enhanced inhibitory abilities than the rest of the groups in the non-verbal task. The distinct sizes of interference from the grammatical gender of the first language across the two bilingual groups is explained by early successive bilinguals’ more enhanced domain-general inhibitory processes in the resolution of between-language conflict at the grammatical gender level relative to late successive bilinguals.

Bilinguals often switch languages as a function of the language background of their addressee. The control mechanisms supporting bilinguals' ability to select the contextually appropriate language are heavily debated. Here we present four experiments in which unbalanced bilinguals named pictures in their first language Dutch and their second language English in mixed and blocked contexts. Immersive virtual reality technology was used to increase the ecological validity of the cued language-switching paradigm. Behaviorally, we consistently observed symmetrical switch costs, reversed language dominance, and asymmetrical mixing costs. These findings indicate that unbalanced bilinguals apply sustained inhibition to their dominant L1 in mixed language settings. Consequent enhanced processing costs for the L1 in a mixed versus a blocked context were reflected by a sustained positive component in event-related potentials. Methodologically, the use of virtual reality opens up a wide range of possibilities to study language and communication in bilingual and other communicative settings.

Little is known about the extent to which information encoding and retrieval differ between materials studied in first and second language (L1 and L2). In this study we compared memory for short, expository texts in L1 and L2, tested with a free recall test and a true/false judgement test. Our results show that students performed at the same level on the recognition test in both languages but not on the free recall test, with much lower performance in L2 than in L1, defined here as the dominant language. The L2 recall cost suggests that students’ performance may be underestimated if they are exclusively tested with essay-type exams in L2.

Code-switching is a common phenomenon that bilinguals engage in, including bilingual children. While many researchers have analyzed code-switching behaviors to better understand more about the language processes in bilingual children, few have examined how code-switching behavior affects a child's linguistic competence. This study thus sought to examine the relationship between code-switching and linguistic competency in bilingual children. Fifty-five English–Mandarin bilingual children aged 5 to 6 years were observed during classroom activities over five days (three hours each day). A number of different word roots and mean length of utterance for both languages, and a number of code-switched utterances for each child, were computed. English receptive vocabulary scores were also obtained. Additionally, teachers rated children's English and Mandarin language competencies approximately six months later. Correlational and hierarchical regression analyses support the argument that code-switching does not indicate linguistic incompetence. Instead, bilingual children's code-switching strongly suggests that it is a marker of linguistic competence.

We examined the influence of bilingualism on task switching by inspecting various markers for task-switching costs. English monolinguals and Korean–English bilinguals completed a modified Dimensional Change Card Sort task based on a nonverbal task-switching paradigm. We found advantages for Korean–English bilinguals in terms of smaller single-task (pure-block) switch costs and greater reactivation benefits than those of English monolinguals. However, bilingual advantages in mixing costs were relatively weak, and the two groups did not differ on local switch costs. Notably, when we approximated the cue-based priming effect in single-task (pure) blocks, we found no evidence that the locus of bilingual advantages in task-switching performance is attributable to a basic cue-priming effect. Taken together, our results suggest that bilingualism is conducive to task switching via facilitation in control processing, including inhibition of proactive interferences and efficient adaptation to abstract task-set reactivation.