Neural circuitry of the bilingual mental lexicon: Effect of age of second language acquisition (original) (raw)
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Human Brain Mapping, 2003
We assessed the effects of age of acquisition and language exposure on the cerebral correlates of lexical retrieval in high-proficient, early-acquisition bilinguals. Functional MRI was used to study Spanish–Catalan bilinguals who acquired either Spanish or Catalan as a first language in the first years of life. Subjects were exposed to the second language at 3 years of age, and have used both languages in daily life since then. Subjects had a comparable level of proficiency in the comprehension of both languages. Lexical retrieval with the verbal fluency task resulted in the well-established pattern of left hemispheric activation centered on the inferior frontal region. The effect of age of acquisition was assessed by dividing the subjects into two groups, on the basis of the language acquired first (Catalan-born or Spanish-born bilinguals). Functional comparisons indicated that less extensive brain activation was associated with lexical retrieval in the language acquired earlier in life. The two groups were also different in language usage/exposure, as assessed with a specific questionnaire; in particular, the exposure to the second language (Spanish) was less intensive in the case of Catalans. This was reflected in a significant interaction, indicating a more extensive activation in Catalans during production in Spanish. Overall, these results indicate that, during a production task, both age of acquisition and language exposure affect the pattern of brain activation in bilinguals, even if both languages are acquired early and with a comparable level of proficiency. Hum. Brain Mapping 19:170–182, 2003. © 2003 Wiley-Liss, Inc.
The bilingual brain. Proficiency and age of acquisition of the second language
Brain, 1998
Functional imaging methods show differences in the pattern of cerebral activation associated with the subject's native language (L1) compared with a second language (L2). In a recent PET investigation on bilingualism we showed that auditory processing of stories in L1 (Italian) engages the temporal lobes and temporoparietal cortex more extensively than L2 (English). However, in that study the Italian subjects learned L2 late and attained a fair, but not an excellent command of this language (low proficiency, late acquisition bilinguals). Thus, the different patterns of activation could be ascribed either to age of acquisition or to proficiency level. In the current study we use a similar paradigm to evaluate the effect of early and late acquisition of L2 in highly proficient bilinguals.
Images of the multilingual brain: The impact of age and manner of L2 acquisition.
Is it the age of second language acquisition (AoA) that primarily determines the manner of cerebral representation of multiple languages in the brain, or is it proficiency? Here, we review recent neuroimaging studies that aimed at investigating AoA effects by comparing early with late (usually with L2 acquisition onset after 6 years of age) bilinguals during a variety of language tasks on a number of languages. Most studies did indeed report AoA effects. Of particular interest is that the region mainly found to functionally differ between early and late bilinguals is the left inferior frontal gyrus, which was modulated during syntactic processing, word generation, and sentence generation. Additionally, differences were observed in gray-matter density of the posterior parietal cortex as well as in right-hemisphere involvement. Interestingly, despite some convergence of findings from a localizational point of view, underlying causes of organizational and functional differences for the effect of AoA on bilingual language processing still remain to be uncovered. Hypotheses currently used for explaining activation differences are described (notably cortical efficiency, executive control, neuroanatomical changes, and right-hemisphere involvement) in relation to AoA and language proficiency.
Brain and Language, 2020
It is controversial as to how age of acquisition (AoA) and proficiency level of the second language influence the similarities and differences between the first (L1) and the second (L2) language brain networks. In this functional MRI study, we used representational similarity analysis to quantify the degree of neural similarity between L1 and L2 during sentence comprehension tasks in 26 adult Chinese-English bilinguals, who learned English as L2 at different ages and had different proficiency levels. We found that although L1 and L2 processing activated similar brain regions, greater neural pattern dissimilarity between L1 and L2 was associated with earlier AoA in the left inferior and middle frontal gyri after the effect of proficiency level was controlled. On the other hand, the association between proficiency level and the neural pattern dissimilarity between L1 and L2 was not significant when the effect of AoA was partialled out. The results suggest that the activity pattern of L2 is more distinct from that of L1 in bilingual individuals who acquired L2 earlier and that the contribution of AoA to the neural pattern dissimilarity is greater than that of proficiency level.
NeuroImage, 2003
The objective of the study was to explore differences in regional fMRI activation topography and lateralization between semantic and phonological tasks performed in English and Spanish in bilingual individuals. Eight bilingual (primary Spanish and secondary Englishspeaking) individuals performed fMRI noun-verb association and rhyming tasks in both Spanish and English. Functional dataset analysis within Statistical Parametric Mapping (SPM99) with overlay on T1-weighted anatomic images was performed. Significantly higher laterality indices were noted in the semantic tasks as compared with the phonological tasks in the anterior regions of interest comprising the frontal and superior temporal lobes. A task subtraction analysis demonstrated right hemispheric (inferior frontal gyrus and supramarginal gyrus) foci of significantly increased activation in the combined language phonological tasks compared to the combined language semantic tasks; similarly prominent right hemispheric activation was seen in the English phonological-English semantic subtraction, but the analogous Spanish task subtraction revealed no task-related differences. This divergence in activation topography between semantic and phonological tasks performed in the nonnative language, but not in the primary language, suggests that neural networks utilized for phonological and semantic language processing in the nonnative language may not be as similar as those in the primary language.
fMRI Study of Sentence Generation by Early Bilinguals Differing in Proficiency Level
The Neuroradiology Journal, 2001
The aim of this study was to identify the functional anatomy of the cerebral speech regions involved in speaking in native and foreign language in the same subject using functional magnetic resonance imaging. Experimental design consisted of two activation runs. Each of them included two kinds of tasks arranged in series of five blocks lasting for 30s. In the experimental condition of the first run subjects were required to speak in their native language and in the second run the task was to speak in the foreign language. In both runs, baseline condition was the same and subjects were supposed to lie silently inside the bore. We observed the influence of proficiency on brain activation. In subjects with equal proficiency in the first and the second language, differences were not observed. In the subjects with unequal proficiency in the first and the second language we observed two main effects. First was difference in the strength and extension of activation, the second effect was activation of new regions for the second language, in which proficiency was lower. Studio con RM funzionale della fraseologia in soggetti bilingue RIASSUNTO-Lo scopo di questo lavoro è quello di identificare l'anatomia funzionale delle regioni cerebrali del linguaggio coinvolte nell'uso della lingua madre e di una lingua straniera, nello stesso soggetto con l'impiego della risonanza magnetica funzionale. Il progetto sperimentale è basato su due sequenze di attivazione, entrambe comprendenti due generi di esercizi ordinate in serie di cinque blocchi della durata di 30 secondi. Nelle condizioni sperimentali della prima sequenza i soggetti sono pregati di parlare nella loro lingua madre, mentre nella seconda sequenza nella lingua straniera. In entrambe le sequenze, il livello di base è identico e i soggetti mantenevano la posizione sdraiata in silenzio nel tunnel. Abbiamo osservato l'influenza del livello di abilità sulla attivazione cerebrale. In soggetti con eguali capacità nelle due lingue non si sono osservate differenze significative. Nei soggetti con capacità diseguali nella prima e nella seconda lingua abbiamo effettuato due principali osservazioni: per prima la differenza in forza ed estensione dell'attivazione e per seconda l'attivazione di nuove regioni per la seconda lingua, nella quale l'abilità era inferiore.
Research has shown that semantic processing of sentences engages more activity in the bilingual com- pared to the monolingual brain and, more specifically, in the inferior frontal gyrus. The present study aims to extend those results and examines whether semantic and also grammatical sentence processing involve different cerebral structures when testing in the native language. In this regard, highly proficient Spanish/Catalan bilinguals and Spanish monolinguals made grammatical and semantic judgments in Spanish while being scanned. Results showed that both types of judgments recruited more cerebral activ- ity for bilinguals in language-related areas including the superior and middle temporal gyri. Such neural differences co-occurred with similar performance at the behavioral level. Taken together, these data sug- gest that early bilingualism shapes the brain and cognitive processes in sentence comprehension even in their native language; on the other hand, they indicate that brain over activation in bilinguals is not con- strained to a specific area.