Neural Mechanism Of Morphological Processing Of Ambiguous Morphemes In Chinese Word Recognition: An FMRI Study

Visual word recognition is a seemingly simple but actually a complex cognitive process.It needs to map any visual symbol to the corresponding semantics.Reading effectively requires perception,cognition and language processes,one of which is morphological processing.In the past,the literature mainly used alphabetic language(derived words or inflection words,but not compound words)to examine morphological processing,trying to explore the independent role of morphemes.However,the available results are mixed and inconsistent.And,to the best of our knowledge,no research has been conducted to clarify the specific role of morphological processing in visual word recognition.The “morphemic ambiguity” phenomenon that exists widely in Chinese(for example,"月",which can mean either “the moon” or “the month”)is very suitable for investigating the nature of morphological processing,because by exploring the activation patterns of ambiguous morphemes with different morphemic meanings,the issue of independent representation of morphemes can be well solved.However,there are great differences in the morphemic meaning frequency of ambiguous morphemes,and the morphemic meaning activation patterns of different types of ambiguous morphemes are likely to be very different.Therefore,this paper adopted Chinese ambiguous morphemes as experimental corpus,and uses balanced ambiguous morphemes(there is no significant difference in the frequency of morphemic meaning)and biased ambiguous morphemes(with dominant meanings)as experimental data by functional magnetic resonance imaging(f MRI),respectively,in an attempt to reveal the neural mechanism of semantic activation of morphemes and the specific role of morphological processing in word recognition.This dissertation consists four studies.Firstly,we examined comprehensively whether balanced ambiguous morphemes differed from biased ambiguous morphemes in morph-semantic activation pattern(Study 1: Behavioral study).The results of ACC showed that the interaction between the ambiguous morpheme types and the prime words type.When the target word contains balanced ambiguous morphemes,the ACC of M+S+(the word pair shared the same ambiguous morpheme with the same meaning)and M+S-(the word pair shared the same ambiguous morpheme but with the different meaning)is significantly higher than that of control condition.When the target word contains biased ambiguous morphemes,it is only found that the ACC of M+S+ is significantly higher than that of M+S-,and the ACC of related conditions of M-S+(word pairs shared the whole-word level meanings)is significantly higher than that of control condition.It shows that the ambiguous morphemes of balanced type and biased type do have different behavior patterns,and contextual information has a greater impact on balanced ambiguous morphemes.Secondly,based on the results of Study 1,the neural patterns of morpheme activation of each ambiguous morpheme were investigated separately.The second study investigated the neural activation patterns of morpheme semantic processing in the process of vocabulary recognition when Chinese compound words contained balanced ambiguity morphemes(Study 2: f MRI study).Compared to the unrelated control condition,the context-supported morphemic meaning was associated with increased activity in the left SFG and bilateral MTG and this priming effect could be dissociated from that of the lexical-level semantic-related condition.In broader brain regions,including the left SFG,bilateral MTG,left STG,right IOG,and left precuneus,the context-unsupported meaning condition showed decreased activity compared with the unrelated control condition.These findings indicate that both the context-supported and-unsupported meanings evoke significant priming effects,however,they differ from each other with different brain basis,providing new insight into the neural correlates of ambiguous morpheme processing.Thirdly,the biased ambiguous morphemes were adopted as experimental materials,we investigated the neural activation pattern of morpho-semantic processing during the Chinese compound words recognition(Study 3: f MRI study).The whole brain analysis’ s results showed that only the left middle frontal gyrus was sensitive to morpho-semantic processing,the context-unsupported meaning condition showed decreased activity compared with the unrelated control condition,but no effect on the context-unsupported meaning(Experiment A).In Experiment B,we investigated the effect of individual differences in words recognition abilities,we found that morphological awareness,reading fluency,productive fluency,phonological awareness and sublexical morphological awareness all played an important role in the morpho-semantic processing,which is reflected in the left middle frontal gyrus,left precuneus lobe and left superior frontal gyrus.Finally,combining to the brain function localization task and prior meta-analysis,based on Dynamic Causal Model,we explored the role of morphological processing during the words recognition(Study 4: f MRI study).When the target word and the priming word have the same morpheme meaning(i.e.,morpheme and whole words share both form and meaning),the condition modulate the “orthography-phonologymeaning” pathway from the visual word form area to the inferior frontal gyrus and then to the left middle temporal gyrus.In addition,the condition also modulates the“orthography-meaning” pathway from the visual word form area to the left middle temporal gyrus.When the target word and the prime word have different morpheme meanings(i.e.,morpheme and whole words share form only),this condition only modulate the “orthography-phonology-meaning” pathway from the visual morphology area to the inferior frontal gyrus and then to the left middle temporal gyrus.When the target word and the prime word have the lexical-level semantic-related,this condition modulates the functional connection of the visual word form area to the left middle temporal gyrus.Take together;the present study explored the neural mechanism of morphosemantic processing during the Chinese compound word recognition.These findings indicate that balanced ambiguous morphemes are more affected by context information than biased ambiguous morphemes,they differ from each other with different brain basis,and it also supported morphological function exist an independent representation,providing new insight into the neural substrates of ambiguous morpheme processing.Additionally,the results are the strongest neuroimaging evidence to date that morphological processing contributes to the dorsal pathway of the "orthography-phonology-meaning" pathway.