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There are very numerous reports in the neuropsychological literature of patients showing, in naming and/or comprehension tasks, a disproportionate deficit for nouns in comparison with verbs or a disproportionate deficit for verbs in comparison with nouns. A number of authors advanced that, in at least some or even in every of these reported cases, the noun/verb dissociation in fact reflected an underlying conceptual deficit disproportionately affecting either object or action concepts. These patterns thus would put an additional constraint on theories of conceptual knowledge organization, which should be able to explain how brain damage could selectively disrupt the concepts of objects or the concepts of actions. We have reviewed 69 papers (published from 1984 to 2009) that reported a pattern of a noun or a verb disproportionate deficit in a single-case, multiple-case, or group study of brain-damaged patients with various aetiologies. From this review, we concluded that none of these studies provided compelling evidence in favour of the interpretation that the observed noun or verb disproportionate deficit arose at the conceptual processing level and, accordingly, that this level may be organized according to the "object/action" dimension. Furthermore, we argue that investigating conceptual impairments in brain-damaged patients according to the "object/action" dichotomy is not empirically fruitful if the purpose is to inform theories of conceptual knowledge organization. In order to provide evidence relevant to these theories, one needs to consider finer grained distinctions within both the object and the action category when investigating the scope of the patients' conceptual impairment.

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We report the results of a single-case study carried out with a brain-damaged patient, G.C., whose conceptual knowledge of living things (animals and plants) was significantly more impaired than his knowledge of artifacts and his knowledge of actions, which were similarly impaired. We examined whether this pattern of conceptual impairment could be accounted for by the "sensory/functional" or the "manipulability" account for category-specific conceptual impairments advocated within the feature-based organization theory. To this end, we assessed, first, the patient's knowledge of sensory compared to functional and motor features and, second, his knowledge of nonmanipulable compared to manipulable items. The findings showed that the patient's disproportionate impairment for living things compared to both artifacts and actions was not associated with a disproportionate impairment of sensory compared to functional or motor knowledge or with a relative sparing of manipulable compared to nonmanipulable items. We then discuss how alternative theories of conceptual knowledge organization could account for G.C.'s pattern of category-specific deficit.

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