Purpose: To understand the developmental changes of semantic processing is crucial to know the nature of the organization of semantic knowledge. Previous studies of semantic processing used cross-sectional approaches to examine developmental changes and did not make distinctions between semantic association and categorical relatedness in typically developing (TD) youths. Moreover, autism spectrum disorders (ASD) are a group of neuro-developmental disorders with communication and semantic processing deficits which have been demonstrated by aberrant neural activity during semantic processing. However, it is little known whether processing categorical relatedness would differ between youths with ASD and TD youths. Behavioral measures and functional magnetic resonance imaging (fMRI) were used to investigate the developmental changes of semantic association and categorical relatedness in TD youths, and to further examine the neural correlates of semantic judgments in the youths with ASD while processing categorical relatedness. Methods: Experiment 1 used a longitudinal approach to investigate the developmental changes of semantic association and categorical relatedness in TD youths. This study orthogonally manipulated the semantic association (strong, weak) and categorical relatedness (high, low) to examine the developmental changes of 12-year-old youths in a two-year interval. Sixteen youths were asked to indicate if character pairs were related in meaning while they underwent fMRI. Experiment 2 used fMRI to examine the neural correlates of semantic processing in youths with ASD and TD youths. Thirty-four male youths with ASD and thirty-five age-, sex-, intelligence quotient (IQ) and handedness-matched TD youths. They were asked to decide whether two visually-presented Chinese characters were semantically related. For the related pairs, categorical relatedness was item-level parametric modulator served as a continuous variable to determine if brain activation was systematically correlated with categorical relatedness.
Results: In Experiment 1, the weak versus the strong semantic association produced greater activation in left inferior frontal gyrus (IFG), and the high versus low categorical relatedness produced greater activation in the left precuneus. Moreover, in age 2, the weak versus strong semantic association produced greater activation in the left IFG, and the high versus low categorical relatedness produced greater activation in the left precuneus. In Experiment 2, for the ASD group, the lower categorical relatedness produced greater activation in the left middle temporal gyrus (BA 21) as compared to the TD group. For the TD group, the higher categorical relatedness produced greater activation in the right precuneus (BA 30) as compared to the ASD group.
Conclusion: First, older children may engage more thoroughly in controlled retrieval and selection of semantic knowledge. Moreover, they may become more adept in processing abstract relationship of categorical relatedness with comparing the overlapping semantic features. Second, our findings imply differential neural mechanisms of processing categorical relatedness between the ASD and the TD group. The ASD group may more rely on access to semantic representations for abstract semantic concepts. In contrast, the TD group may use more abstract and sophisticated manners to integrate different categorical relationships. Altogether, our findings suggest developmental changes in TD youths’ semantic processing by association strength and in the organization of semantic knowledge by categorical relatedness; furthermore, the youths with ASD and TD youths may use different manners for semantic judgments.
Keywords: Autism spectrum disorders (ASD), categorical relatedness, development, semantic association