| Studies of inflectional languages have demonstrated that Broca's aphasics find it more difficult to produce verbs than nouns, while Wernicke's aphasics show the opposite profile. Explanations for this double dissociation include several single-factor accounts such as grammatical accounts (e.g., verb deficits reflect the greater morphological or syntactic complexity of verbs), semantic-conceptual accounts (e.g., verbs are based on action meanings, which are stored in anterior motor regions; nouns are based on object meanings, which are stored in sensory cortex), and lexical accounts (verbs and nouns are stored in separate regions of the brain, independent of their semantic content). In Chinese, many words are compounds with a complex internal structure, including VN compound verbs like "SHUI-JIAO" (literally sleep-sleep, meaning "to sleep") and VN compound nouns like "FEI-JI" (literally fly-machine, meaning "airplane"). Hence, noun-verb dissociations between Broca's aphasics and Wernicke's aphasics may occur at the lexical level and the sublexical level. Such sublexical dissociation would provide a challenge to existing explanations. To explore this possibility, an object and action naming study was conducted with Chinese Broca's and Wernicke's aphasics, designed to elicit several different compound types (VN nouns, VN verbs, NN nouns, VNN nouns, and NNN nouns). Results of the present study demonstrate both lexical and sublexical noun-verb dissociations between Broca's aphasics and Wernicke's aphasics, and provide evidence for the interaction of sublexical noun-verb dissociations with word structure frequency, e.g., sublexical noun-verb dissociations are significant in non-major word types but are insignificant in major word types. Additionally, a frequency effect is observed in the access of whole words, components, and word structures, e.g., the more complex two-morpheme word structure has higher accessibility than the simpler single-morpheme word structure. The presence of noun-verb dissociations at the lexical and the intra-lexical levels and their interaction with frequency effects cannot be explained by any single-factor account discussed above. However, the complex phenomenon observed in Chinese aphasia can be accounted for by connectionist models such as the Competition Model, which consider the interaction of relevant factors at both lexical and intra-lexical levels. |
