Learning to read words in a new language shapes the neural organization of the prior languages

Processing negative emotion in two languages of bilinguals: Accommodation and assimilation of the neural pathways based on a meta-analysis

Numerous functional magnetic resonance imaging (fMRI) studies have examined the neural mechanisms of negative emotional words, but scarce evidence is available for the interactions among related brain regions from the functional brain connectivity perspective. Moreover, few studies have addressed the neural networks for negative word processing in bilinguals. To fill this gap, the current study examined the brain networks for processing negative words in the first language (L1) and the second language (L2) with Chinese-English bilinguals. To identify objective indicators associated with negative word processing, we first conducted a coordinate-based meta-analysis on contrasts between negative and neutral words (including 32 contrasts from 1589 participants) using the activation likelihood estimation method. Results showed that the left medial prefrontal cortex (mPFC), the left inferior frontal gyrus (IFG), the left posterior cingulate cortex (PCC), the left amygdala, the left inferior temporal gyrus (ITG), and the left thalamus were involved in processing negative words. Next, these six clusters were used as regions of interest in effective connectivity analyses using extended unified structural equation modeling to pinpoint the brain networks for bilingual negative word processing. Brain network results revealed two pathways for negative word processing in L1: a dorsal pathway consisting of the left IFG, the left mPFC, and the left PCC, and a ventral pathway involving the left amygdala, the left ITG, and the left thalamus. We further investigated the similarity and difference between brain networks for negative word processing in L1 and L2. The findings revealed similarities in the dorsal pathway, as well as differences primarily in the ventral pathway, indicating both neural assimilation and accommodation across processing negative emotion in two languages of bilinguals.

Task modulates the orthographic and phonological representations in the bilateral ventral Occipitotemporal cortex

As a key area in word reading, the left ventral occipitotemporal cortex is proposed for abstract orthographic processing, and its middle part has even been labeled as the visual word form area. Because the definition of the VWFA largely varies and the reading task differs across studies, the function of the left ventral occipitotemporal cortex in word reading is continuingly debated on whether this region is specific for orthographic processing or be involved in an interactive framework. By using representational similarity analysis (RSA), this study examined information representation in the VWFA at the individual level and the modulatory effect of reading task. Twenty-four subjects were scanned while performing the explicit (i.e., the naming task) and implicit (i.e., the perceptual task) reading tasks. Activation analysis showed that the naming task elicited greater activation in regions related to phonological processing (e.g., the bilateral prefrontal cortex and temporoparietal cortex), while the perceptual task recruited greater activation in visual cortex and default mode network (e.g., the bilateral middle frontal gyrus, angular gyrus, and the right middle temporal gyrus). More importantly, RSA also showed that task modulated information representation in the bilateral anterior occipitotemporal cortex and VWFA. Specifically, ROI-based RSA revealed enhanced orthographic and phonological representations in the bilateral anterior fusiform cortex and VWFA in the naming task relative to the perceptual task. These results suggest that lexical representation in the VWFA is influenced by the demand of phonological processing, which supports the interactive account of the VWFA.

Language distance in orthographic transparency affects cross-language pattern similarity between native and non-native languages

How native and non-native languages are represented in the brain is one of the most important questions in neurolinguistics. Much research has found that the similarity in neural activity of native and non-native languages are influenced by factors such as age of acquisition, language proficiency, and language exposure in the non-native language. Nevertheless, it is still unclear how the similarity between native and non-native languages in orthographic transparency, a key factor that affects the cognitive and neural mechanisms of phonological access, modulates the cross-language similarity in neural activation and which brain regions show the modulatory effects of language distance in orthographic transparency. To address these questions, the present study used representational similarity analysis (RSA) to precisely estimate the neural pattern similarity between native language and two non-native languages in Uyghur-Chinese-English trilinguals, whose third language (i.e., English) was more similar to the native language (i.e., Uyghur) in orthography than to their second language (i.e., Chinese). Behavioral results revealed that subjects responded faster to words in the non-native language with more similar orthography to their native language in the word naming task. More importantly, RSA revealed greater neural pattern similarity between Uyghur and English than between Uyghur and Chinese in select brain areas for phonological processing, especially in the left hemisphere. Further analysis confirmed that those brain regions represented phonological information. These results provide direct neuroimaging evidence for the modulatory effect of language distance in orthographic transparency on cross-language pattern similarity between native and non-native languages during word reading.

Mechanisms for Auditory Perception: A Neurocognitive Study of Second Language Learning of Mandarin Chinese

Speech perception is an important early skill for language learning. This study uses functional magnetic resonance imaging (fMRI) to examine the relationship between auditory perception abilities and second language (L2) vocabulary learning in an effort to explore behavior-brain correlations. Twenty-one English monolinguals learned 48 auditory Chinese pseudowords over six weeks. Their pre-training abilities in non-linguistic pitch and linguistic tone perception significantly and positively predicted their novel word-learning performance, which correlated with their brain response patterns in the left Heschl’s gyrus. Analyses of regions of interest (ROIs) showed coactivation of the frontal and temporal regions during novel lexical retrieval, and the non-linguistic pitch perception ability modulated brain activations in these regions. Effective connectivity analyses further indicated a collaboration of a ventral stream for speech perception and a dorsal stream for sensory-motor mapping in the L2 network. The ventral stream, compared with the dorsal stream, played a more dominant role in auditory word learning as the L2 proficiency increased. Better pitch and tone perception abilities strengthened the ventral pathways and decreased the reliance on frontal regions. These findings are discussed in light of current models of speech processing and L2 learning.

Lexical learning in a new language leads to neural pattern similarity with word reading in native language

Previous neuroimaging studies have suggested similar neural activations for word reading in native and second languages. However, such similarities were qualitatively determined (i.e., overlapping activation based on traditional univariate activation analysis). In this study, using representational similarity analysis and an artificial language training paradigm, we quantitatively computed cross-language neural pattern similarity to examine the modulatory effect of proficiency in the new language. Twenty-four native Chinese speakers were trained to learn 30 words in a logographic artificial language for 12 days and scanned while performing a semantic decision task after 4-day training and after 12-day training. Results showed that higher proficiency in the new language was associated with higher cross-language pattern similarity in select regions of the reading network.

Neural Pattern Similarity in the Left IFG and Fusiform Is Associated with Novel Word Learning

Previous studies have revealed that greater neural pattern similarity across repetitions is associated with better subsequent memory. In this study, we used an artificial language training paradigm and representational similarity analysis to examine whether neural pattern similarity across repetitions before training was associated with post-training behavioral performance. Twenty-four native Chinese speakers were trained to learn a logographic artificial language for 12 days and behavioral performance was recorded using the word naming and picture naming tasks. Participants were scanned while performing a passive viewing task before training, after 4-day training and after 12-day training. Results showed that pattern similarity in the left pars opercularis (PO) and fusiform gyrus (FG) before training was negatively associated with reaction time (RT) in both word naming and picture naming tasks after training. These results suggest that neural pattern similarity is an effective neurofunctional predictor of novel word learning in addition to word memory.

Native-Language Phonological Interference in Early Hakka-Mandarin Bilinguals' Visual Recognition of Chinese Two-Character Compounds: Evidence from the Semantic-Relatedness Decision Task

Previous research has indicated that, in viewing a visual word, the activated phonological representation in turn activates its homophone, causing semantic interference. Using this mechanism of phonological mediation, this study investigated native-language phonological interference in visual recognition of Chinese two-character compounds by early Hakka-Mandarin bilinguals. A visual semantic-relatedness decision task in Chinese was given to native Mandarin speakers and early Hakka-Mandarin bilinguals. Both participant groups made more false positive errors and responded more slowly to the pair of two-character compounds containing a homophone; but only Hakka-Mandarin bilinguals made more false positive errors and responded more slowly to the pair containing a near-homophone. We concluded that phonology is needed in both native and nonnative speakers' meaning access of Chinese two-character compounds and that native-language phonological interference is universal in L2 visual word recognition, not language type dependent; phonological and orthographic information are "interactive-compensatory" in helping Hakka readers' resolve the interference.

L1 and L2 processing in the bilingual brain: A meta-analysis of neuroimaging studies

Neuroimaging studies investigating bilingual processes have produced controversial results in determining similarities versus differences between L1 and L2 neural networks. The current meta-analytic study was conducted to examine what factors play a role in the similarities and differences between L1 and L2 networks with a focus on age of acquisition (AOA) and whether the orthographic transparency of L2 is more or less transparent than that of L1. Using activation likelihood estimation (ALE), we found L2 processing involved more additional regions than L1 for late bilinguals in comparison to early bilinguals, suggesting L2 processing is more demanding in late bilinguals. We also provide direct evidence that AOA of L2 influences L1 processing through the findings that early bilinguals had greater activation in the left fusiform gyrus than late bilinguals during L1 processing even when L1 languages were the same in the two groups, presumably due to greater co-activation of orthography in L1 and L2 in early bilinguals. In addition, we found that the same L2 languages evoked different brain activation patterns depending on whether it was more or less transparent than L1 in orthographic transparency. The bilateral auditory cortex and right precentral gyrus were more involved in shallower-than-L1 L2s, suggesting a "sound-out" strategy for a more regular language by involving the phonological regions and sensorimotor regions to a greater degree. In contrast, the left frontal cortex was more involved in the processing of deeper-than-L1 L2s, presumably due to the increased arbitrariness of mapping between orthography and phonology in L2.

Long-term experience with Chinese language shapes the fusiform asymmetry of English reading

Previous studies have suggested differential engagement of the bilateral fusiform gyrus in the processing of Chinese and English. The present study tested the possibility that long-term experience with Chinese language affects the fusiform laterality of English reading by comparing three samples: Chinese speakers, English speakers with Chinese experience, and English speakers without Chinese experience. We found that, when reading words in their respective native language, Chinese and English speakers without Chinese experience differed in functional laterality of the posterior fusiform region (right laterality for Chinese speakers, but left laterality for English speakers). More importantly, compared with English speakers without Chinese experience, English speakers with Chinese experience showed more recruitment of the right posterior fusiform cortex for English words and pseudowords, which is similar to how Chinese speakers processed Chinese. These results suggest that long-term experience with Chinese shapes the fusiform laterality of English reading and have important implications for our understanding of the cross-language influences in terms of neural organization and of the functions of different fusiform subregions in reading.