Developmental changes in the neural influence of sublexical information on semantic processing

Neural substrates of L2-L1 transfer effects on phonological awareness in young Chinese-English bilingual children

The growing trend of bilingual education between Chinese and English has contributed to a rise in the number of early bilingual children, who were exposed to L2 prior to formal language instruction of L1. The L2-L1 transfer effect in an L1-dominant environment has been well established. However, the threshold of L2 proficiency at which such transfer manifests remains unclear. This study investigated the behavioral and neural processes involved when manipulating phonemes in an auditory phonological task to uncover the transfer effect in young bilingual children. Sixty-two first graders from elementary schools in Taiwan were recruited in this study (29 Chinese monolinguals, 33 Chinese-English bilinguals). The brain activity was measured using fNIRS (functional near-infrared spectroscopy). Bilingual children showed right lateralization to process Chinese and left lateralization to process English, which supports more on the accommodation effect within the framework of the assimilation-accommodation hypothesis. Also, compared to monolinguals, bilingual children showed more bilateral frontal activation in Chinese, potentially reflecting a mixed influence from L2-L1 transfer effects and increased cognitive load of bilingual exposure. These results elucidate the developmental adjustments in the neural substrates associated with early bilingual exposure in phonological processing, offering valuable insights into the bilingual learning process.

Neural sensitivity to semantic neighbors is stable across the adult lifespan

As we age, language reflects patterns of both stability and change. On the one hand, vocabulary and semantic abilities are largely stable across the adult lifespan, yet lexical retrieval is often slower and less successful (i.e., slower picture naming times, increased tip of the tongue incidents). Although the behavioral bases of these effects have been well established, less is known about the brain regions that support these age-related differences. We used functional Magnetic Resonance Imaging (fMRI) to examine the neural basis of picture naming. Specifically, we were interested in whether older adults would be equally sensitive to semantic characteristics, specifically the number of semantic near neighbors. Near neighbors, defined here as items with a high degree of semantic feature overlap, were of interest as these are thought to elicit competition among potential candidates and increase naming difficulty. Consistent with prior reports, pictures with more semantic near neighbors were named more slowly and less accurately for all adults. Additionally, this interference for naming times was larger as age increased, starting around 30 years old. In contrast to the age-related behavioral slowing, the neural basis of these effects was stable across adulthood. Across all adults, a number of language-relevant regions including left posterior middle temporal gyrus and left inferior frontal gyrus, pars triangularis were sensitive to the number of near neighbors. Our results suggest that although middle-aged and older adults' picture naming is more slowed by increased semantic competition, the brain regions supporting semantic processes remain stable across the adult lifespan.

Neuro-Cognitive Differences in Semantic Processing Between Native Speakers and Proficient Learners of Mandarin Chinese

The present study aimed to investigate the neural mechanism underlying semantic processing in Mandarin Chinese adult learners, focusing on the learners who were Indo-European language speakers with advanced levels of proficiency in Mandarin Chinese. We used functional magnetic resonance imaging technique and a semantic judgment task to test 24 Mandarin Chinese adult learners (L2 group) and 26 Mandarin Chinese adult native speakers (L1 group) as a control group. In the task, participants were asked to indicate whether two-character pairs were related in meaning. Compared to the L1 group, the L2 group had greater activation in the bilateral occipital regions, including the fusiform gyrus and middle occipital gyrus, as well as the right superior parietal lobule. On the other hand, less activation in the bilateral temporal regions was found in the L2 group relative to the L1 group. Correlation analysis further revealed that, within the L2 group, increased activation in the left middle temporal gyrus/superior temporal gyrus (M/STG, BA 21) was correlated with higher accuracy in the semantic judgment task as well as better scores in the two vocabulary tests, the Assessment of Chinese character list for grade 3 to grade 9 (A39) and the Peabody Picture Vocabulary Test-Revised. In addition, functional connectivity analysis showed that connectivity strength between the left fusiform gyrus and left ventral inferior frontal gyrus (IFG, BA 47) was modulated by the accuracy in the semantic judgment task in the L1 group. By contrast, this modulation effect was weaker in the L2 group. Taken together, our study suggests that Mandarin Chinese adult learners rely on greater recruitment of the bilateral occipital regions to process orthographic information to access the meaning of Chinese characters. Also, our correlation results provide convergent evidence that the left M/STG (BA 21) plays a crucial role in the storage of semantic knowledge for readers to access to conceptual information. Moreover, the connectivity results indicate that the left ventral pathway (left fusiform gyrus-left ventral IFG) is associated with orthographic-semantic processing in Mandarin Chinese. However, this semantic-related ventral pathway might require more time and language experience to be developed, especially for the late adult learners of Mandarin Chinese.

Neural correlates of association strength and categorical relatedness in youths with autism spectrum disorder

Impaired language and communication are commonly observed in youths with autism spectrum disorders (ASDs). However, the organization of semantic knowledge in youths with ASD remains unclear compared to typically developing (TD) youths. The present study addresses this issue by using functional magnetic resonance imaging (fMRI) to examine the distinction between association strength and categorical relatedness of semantic knowledge. A sample of 31 male youths with ASD (mean age = 12.1 years, SD = 1.2) and 38 TD youths (mean age = 11.9 years, SD = 1.0) was recruited with matched age, gender, and handedness. Participants decided if two visually presented Chinese characters were semantically related during fMRI scanning. For weaker association strength, the ASD group showed greater left cuneus activation, which was positively correlated with the picture completion for visual perception, whereas the TD group showed greater middle temporal gyrus and inferior frontal gyrus activation. For higher categorical relatedness, the TD group showed greater activation than the ASD group in the occipitotemporal cortex and left precuneus, which was positively correlated with the similarities for concept formulation. Findings imply that the ASD group may use lower-level visual information for both association strength and categorical relatedness. The TD group showed higher-level controlled processes of more elaborate semantic representations for association strength and more elaborate features of categorical knowledge for semantic selection and integration. Autism Res 2019, 12: 1484-1494. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Individuals with autism spectrum disorder (ASD) often present language/communication impairments. Exploring the difference of semantic processing between youths with ASD and typically developing (TD) youths is crucial for understanding the organization of semantic knowledge. We found different neural substrates of semantic knowledge between these two groups. ASD youths may rely more on lower-level visual information during semantic judgments, whereas TD youths showed higher-level controlled processes of more elaborate semantic representations for selection and integration of words, phrases, and sentences.

Developmental changes of association strength and categorical relatedness on semantic processing in the brain

Semantic knowledge has thematic relations of contiguity based on association and taxonomic relations of similarity based on shared features to form categories. It is unknown if there are distinct brain networks between thematic and taxonomic organizations in children and if this distinction is related to changes in specialized brain regions with age and/or skill. We orthogonally manipulated association strength (strong, weak) and categorical relatedness (high, low) to examine 10- to 14-year-old children over a two-year interval. Moreover, we examined whether initial behavioral performance predicted brain activation changes. Weak versus strong association strength produced greater activation over time in left middle temporal gyrus and inferior frontal gyrus, and initial accuracy predicted activation changes in the latter. Moreover, high versus low categorical relatedness produced greater activation over time in left occipito-temporal cortex and precuneus, and initial accuracy predicted activation changes in the latter. These developmental findings suggest different organization for thematic and taxonomic relations.

Temporo-parietal connectivity uniquely predicts reading change from childhood to adolescence

Previous research has shown that left posterior middle temporal gyrus (pMTG) is a core node in the semantic network, and cross-sectional studies have shown that activation in this region changes developmentally and is related to skill measured concurrently. However, it is not known how functional connectivity with this region changes developmentally, and whether functional connectivity is related to future gains in reading. We conducted a longitudinal functional magnetic resonance imaging (fMRI) study in 30 typically developing children (aged 8-15) to examine whether initial brain measures, including activation and connectivity, can predict future behavioral improvement in a semantic judgment task. Participants were scanned on entering the study (time 1, T1) and a follow-up period of 2years (time 2, T2). Character pairs were arranged in a continuous variable according to association strength (i.e. strong versus weak), and participants were asked to determine if these visually presented pairs were related in meaning. Our results demonstrated greater developmental changes from time 1 to time 2 for weaker association pairs in the left pMTG for the children (aged 8-11) as compared to the adolescents (aged 12-15). Moreover, the results showed greater developmental changes from time 1 to time 2 for weaker association pairs in connectivity between the pMTG and inferior parietal lobule (IPL) for the children as compared to the adolescents. Furthermore, a hierarchical stepwise regression model revealed that connectivity between the pMTG and IPL in weak association pairs was uniquely predictive of behavioral improvement from time 1 to time 2 for the children, but not the adolescents. Taken together, the activation results suggest relatively rapid development before adolescence of semantic representations in the pMTG. Moreover, the connectivity results of pMTG with IPL tentatively suggest that early development of semantic representations may be facilitated by enhanced engagement of phonological short-term memory.