Most of us would like to believe that the different patterns of language breakdown observed in aphasic patients reflect the way that the human mind and brain are organized for language. However, because so much modern research on aphasia has been carried out in English, it is difficult to separate universal mechanisms from language-specific content. Crosslinguistic com-parisons permit us to disentangle these confounds, while we address one of the most important issues in cognitive neurobiology, the issue of behavioral and neural plasticity: How many different forms can the language processor take under a range of normal and abnormal conditions? We must have an answer to this question if we want to understand what the neural mechanisms responsible for language

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.

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Double dissociations play an important role in neuropsychology, but they are often identified through subjective estimates of ‘‘high’ ’ versus ‘‘low’ ’ performance, without considering the probability that such an outcome might have occurred by chance. To determine whether two measures ‘‘come apart’ ’ in an interesting way in brain-damaged patients, it is important to know the degree to which variance in one measure can be predicted by variance in the other. This study introduces a statistical procedure to determine the probability of a double dissociation when the correlation between measures is taken into account. Different quantitative definitions of dissociations were compared in two large samples of neurological patients, and applied to four pairs of measures (two for language, two for hemispatial neglect) with different degrees of intercorrelation (ranging from þ.21 to þ.84). If the correlation between measures is not taken into account, large numbers of dissociated cases may be missed, especially for measures that are highly correlated. There are also qualitative differences between methods in the identity of those individuals who meet each definition. Early in the 19th century, investigators interested in the relations between brain and mental faculties became involved in the search for

and acquisition in this language. D 2004 Elsevier Inc. All rights reserved. Keywords: Noun; Verb; Chinese; fMRI Introduction A central issue in the cognitive neuroscience of language is how the brain represents linguistic categories such as nouns, verbs, and adjectives. Neuropsychological studies of brain-injured patients and neuroimaging studies of normal speakers have both suggested specific brain areas that respond to different linguistic categories, in particular, object names (nouns) and action names (verbs). For example, while Broca's aphasics have significant problems with action/verb naming, Wernicke's aphasics typically experience difficulties in producing nouns (Bates et al., 1991; Caramazza and Hillis, 1991; Miceli et al., 1988; Shapiro and Caramazza, 2003). PET studies reveal that nouns and verbs elicit responses from different regions of the brain: nouns or object names activate the posterior regions (occipitotemporal areas, including the visual cortex) while verbs or

Neuropsychological studies have demonstrated that the production of nouns and verbs can be dissociated in aphasia. These reports have been taken as evidence for separate representations of nouns and verbs in the human brain. We used whole-head magnetoencephalography to record cortical dynamics of action and object naming in 10 healthy adults and in 1 anomic patient with superior naming of verbs compared with nouns due to a left posterior parietal lesion. A single set of 100 line drawings was used for both action and object naming. In normal subjects, the activation sequences in action and object naming were essentially identical, advancing from the occipital to posterior temporoparietal and further to the left frontal cortex, without consistent involvement of the classical left inferior frontal (Broca) and temporal (Wernicke) language areas. In the anomic patient, pronounced differences between action and object naming emerged in the left hemisphere. The activation sequence was disrupted at the level of the damaged parietal cortex and did not reach the left frontal cortex even in the relatively easier action naming. The more severely impaired object naming was associated with exceptionally strong and early activation of the left inferior frontal cortex (Broca) and subsequent pronounced activation of the left middle temporal cortex, silent in action naming. Verb and noun retrieval thus utilized a spatiotemporally similar neuronal network in healthy individuals. A clear dissociation in cortical correlates of verb and noun retrieval only became evident in our anomic patient, in whom damage to the language network has resulted in disproportionately worse performance in object than action naming.

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We present a computational model of grammar learning that combines domain-general learning mechanisms with rich representations of linguistic knowledge, world knowledge and situational and discourse context. These representations support processes of language understanding and inference (including both constructional analysis and reference resolution) that help the learner make sense of utterances in context. The learner then draws on generalization and statistical induction techniques to form new constructions that better capture correlations between linguistically identified and contextually inferred information. Our work is part of the larger Neural Theory of Language (NTL) project, whose goal is to build models of cognition and language that satisfy convergent constraints from biology, psychology, linguistics and computation (Chang,