The organization of the conceptual system: The case of the “object versus action” dimension

Abstract

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.

Keywords:

• Organization of conceptual knowledge
• Object concepts
• Action concepts

Acknowledgments

We are indebted to David Kemmerer and an anonymous reviewer for their thoughtful and detailed comments on a previous version of this paper. This research was supported by the Fonds National de la Recherche Scientifique (FNRS) Grants 1.5.193.01 and 1.5.191.04 to Agnesa Pillon.

Notes

¹ Another interpretation has been suggested for these patterns of grammatical category-specific deficits that were found in only one, spoken or written, word processing modality. This interpretation assumed that the conceptual representations of actions and objects are subserved by spatially segregated systems. Damage to the pathway from one of these systems to one modality-specific lexical system would result in a modality-specific deficit for either actions—that is, typically, verbs—or objects—that is, typically, nouns (e.g., Damasio & Tranel, 1993; Rapp & Caramazza, 1998). Although this account cannot be rejected, it needs independent evidence supporting its initial assumption—namely, that the concepts of actions and objects are subserved by segregated systems—just the evidence we are arguing here is lacking.

² Admittedly, any pattern of noun/verb dissociation that is inconsistent across tasks or processing modalities does not necessarily result or does not result only from a deficit located at a nonsemantic (lexical or visual) level of processing. To begin with, inconsistencies could result from an insufficient control of the extraneous variables affecting the performance in each task or processing modality. Furthermore, inconsistencies could be due to some modality- or task-specific processing demands that interact with grammatical category. For instance, it could be argued that performance in a comprehension task is facilitated when probed from pictures compared to words but only for objects (nouns), not for actions (verbs), because, say, in the case of objects but not of actions, the visual-to-conceptual mapping is less arbitrary than the word-to-conceptual mapping (i.e., in the picture modality, the visual properties of an object, but not of an action, could directly activate some of its conceptual properties). However, maintaining a semantic account for the noun/verb dissociation in such cases would require a developed analysis of the task demands and a motivated hypothesis about why these would differ according to grammatical category—an approach that was not attempted in the studies reported.

³ Except that Boswell could not retrieve the concepts of animals (but only these concepts within the noun set; the concepts of vegetables and tools/utensils were not impaired).

⁴ Let us mention that, within the domain-specific knowledge theory (Caramazza & Shelton, 1998; Mahon & Caramazza, 2009) as well, the concepts of tools could dissociate from the concepts of other artifacts (i.e., furniture, vehicles, clothing) in the case of brain damage, although for another principled reason. Tools, like conspecifics, animals, and plants, would be a category of objects whose efficient recognition and use had fitness value in human evolution and, hence, would be processed by a dedicated domain-specific conceptual system. This theory is silent, however, on the status of action concepts within the conceptual system.