The dissociation between nouns and verbs in Broca's and Wernicke's aphasia: findings from Chinese

Studies in English and Italian have shown that non-fluent Broca's aphasics find it more difficult to produce verbs than nouns, while some fluent patients (including Wernicke's aphasics and anomics) show the opposite profile. Explanations for this double dissociation include grammatical accounts (e.g. verb deficits reflect differences in morphological and/or syntactic complexity), 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 'LOOK-BOOK' ('read') and VN compound nouns like 'STAND-GOOSE' ('penguin'). Hence words may be nouns at the lexical level, but they contain verbal elements at the sublexical level, providing a challenge to existing explanations for the noun-verb dissociation. 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, VNN nouns, NNN nouns and NN nouns). We replicate the noun-verb double dissociation at the whole-word level, and provide further evidence for a double dissociation at the sublexical level: Broca's err more often on the verb morpheme within VN nouns as well as VN verbs; Wernicke's err more often on noun morphemes, and they often produce verb morphemes where none are required (e.g. substituting VV for NN words). Hence explanations for the noun-verb dissociation must apply at both the lexical and the sublexical level, a problem for all current accounts.