At the edge of semantic space: The breakdown of coherent concepts in semantic dementia is constrained by typicality and severity but not modality

Emily J. Mayberry, Karen Sage, Matthew A. Lambon Ralph

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    Abstract

    Hub-and-spoke models of semantic representation suggest that coherent concepts are formed from the integration of multiple, modality-specific information sources with additional modality-invariant representations-most likely stored in the ventrolateral anterior temporal lobe (vATL). As well as providing the necessary computational mechanisms for the complexities of feature integration, these modality-invariant representations also license a key aspect of semantic memory-semantic-based generalization. Semantic dementia allows us to investigate this aspect of conceptual knowledge because (a) the patients have a selective and progressive semantic degradation and (b) this is associated with profound ventrolateral ATL atrophy. Specifically, the boundaries between concepts become degraded in semantic dementia and, when tested using the appropriate materials, the patients make simultaneous under- and overgeneralization errors. We found that the rate of these errors were a function of typicality and psuedotypicality of the items as well as the severity of the patients' semantic impairment. Following the modality-invariant nature of the vATL hub representation, we also confirmed that the patients were impaired on both verbal- and picture-based versions of the same task. © 2011 Massachusetts Institute of Technology.
    Original languageEnglish
    Pages (from-to)2240-2251
    Number of pages11
    JournalJournal of Cognitive Neuroscience
    Volume23
    Issue number9
    DOIs
    Publication statusPublished - Sept 2011

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