The organization of conceptual knowledge: the evidence from category-specific semantic deficits

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Abstract

Questions about the organization of conceptual knowledge in the human brain can be addressed by studying patients with category-specific semantic deficits: disproportionate and even selective impairment of conceptual knowledge of one category of objects compared with other categories. Recently, consensus has emerged regarding the basic facts of category-specific semantic deficits: (1) the categories that can be disproportionately impaired or spared are ‘animals’, ‘fruit/vegetables’, and ‘artifacts’; and (2) category-specific semantic deficits are not associated with disproportionate deficits for a type or modality of knowledge. Together with findings in functional neuroimaging, these data indicate a complex organization of conceptual knowledge characterized by several independent dimensions of organization.

Section snippets

The Sensory/Functional theory

The original formulation of the Sensory/Functional theory by Warrington and collaborators 1, 2, 3 made two basic assumptions: (1) the semantic system is organized into modality-specific semantic subsystems (e.g. visual/perceptual, functional/associative); and (2) the ability to recognize/name living things differentially depends on visual/perceptual information, whereas the ability to recognize/name non-living things differentially depends on functional/associative information (for related

The Organized-Unitary-Content hypothesis

Although early discussions of the organization of the conceptual system focused on the assumption that conceptual knowledge is organized into modality-specific subsystems [32], some authors argued against this hypothesis and in favor of a unitary, amodal system of conceptual organization 33, 34, 35. The Organized-Unitary-Content hypothesis (OUCH) [34] is one such proposal. OUCH makes two basic assumptions: (1) conceptual features corresponding to object properties that often co-occur will be

Interim summary and directions

The three proposals reviewed above (the Sensory/Functional theory, the Domain-Specific hypothesis, and the Conceptual-Structure account) are contrary hypotheses of the causes of category-specific semantic deficits. However, the individual assumptions that comprise each account are not necessarily mutually contrary. For instance, whereas the Sensory/Functional theory can be rejected as a viable hypothesis of the causes of category-specific semantic deficits, it remains an open question as to

Clues from functional neuroimaging

In this section we address two questions: (1) Is there evidence from functional neuroimaging that different areas of the brain are differentially involved in processing/storing information corresponding to different categories of objects? (2) If so, do such data motivate the assumption that one constraint on the physical distribution of conceptual information in the brain is type or modality of information? We note at the outset that the scope of the empirical review to follow is limited to an

Conclusion

We have evaluated three hypotheses of the causes of category-specific semantic deficits. The basic predictions made by the Sensory/Functional theory 1, 2, 3, which was until recently the received view, are at variance with the facts of category-specific semantic deficits. The OUCH model [33] is not inconsistent with the facts of category-specific deficits but is too underdeveloped to provide a useful framework for interpreting those facts. When OUCH-type models have been elaborated to the point

Acknowledgements

The preparation of this article was supported in part by NIH grant DC 04542 to Alfonso Caramazza. We thank Erminio Capitani, Argye Hillis, Marcella Laiacona, and Jenni Shelton Young for sharing with us their ideas on the nature of category-specific semantic deficits, and Alex Martin and Lauren Moo for helping us to understand the neuroimaging data on conceptual knowledge. We also thank Joe Devlin and the anonymous reviewers for helpful comments on an earlier version of this paper.

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