Effects of Vocabulary Sizes on Semantic Processing to Chinese Characters between Fifth Graders and Adults

Purpose: Although many studies have focused on the effects of vocabulary sizes on orthographic and phonological processes to Chinese characters, few studies have explored the effects of vocabulary sizes on semantic processing. Experiments 1-3 used behavioral paradigms with an auditory semantic judgment to evaluate the differences between fifth graders and adults, as well as differences between fifth graders with different vocabulary sizes. In Experiment 4, functional Magnetic Resonance Imaging (fMRI) was used to examine the neural correlates of auditory semantic judgments to Chinese characters in a group of 10-21 year old Chinese participants. Methods: Semantic association strength was varied (stronger, weaker, and unrelated). Participants were asked to decide if two Chinese characters were semantically related. Results: In Experiments 1-3, lower accuracy and longer reaction time were found for weaker association, as compared to stronger association strength. The difference of stronger and weaker association strength was larger for adults than the difference of stronger and weaker association strength for fifth graders. Fifth graders with larger vocabulary sizes showed better performance for both stronger and weaker association strength, as compared to fifth graders with fewer vocabulary sizes. In Experiment 4, characters with stronger semantic association elicited greater activation in left inferior parietal lobule (IPL, BA 39, 40), and characters with weaker semantic association elicited activation in left inferior frontal gyrus (IFG, BA 45). Regarding developmental changes, increasing age was correlated with greater activation in left middle temporal gyrus (BA 21) and left IFG (BA 45) for related pairs, and in left IFG (BA47) for unrelated pairs. Conclusions: Effects of age and vocabulary sizes are related to semantic processing. Fifth graders show poorer search and integration of semantic features during semantic judgments as compared to adults. Fifth graders with fewer vocabulary sizes show deficient mappings among semantics, phonology, and orthography, producing poorer performance on meaning judgments as compared to fifth graders with larger vocabulary sizes. Characters with stronger semantic association elicited greater activation in left IPL(BA 39, 40) for semantic features integration, and characters with weaker semantic association elicited greater activation in left IFG (BA 45) for greater engagement of selection among homophones for Chinese characters. The developmental changes suggest greater integration of semantic and phonological processes to select the correct answer among homophones for related pairs, and demanding retrieval processes to judge unrelated pairs for older children.