Explaining category-related effects in the retrieval of conceptual and lexical knowledge for concrete entities: operationalization and analysis of factors.

Category-related effects in the retrieval of conceptual and lexical knowledge for concrete entities have been well documented in lesion studies, and also with functional imaging and electrophysiological approaches. For example, brain-damaged subjects may be impaired in the ability to recognize or to name animals but not tools, or the opposite pattern may obtain. One reason for these dissociations is that different patterns of defects tend to be caused by distinct lesion profiles, suggesting a relative tendency for certain neural systems to be involved in category-related knowledge. But we and others have also hypothesized that a variety of traits of concrete entities co-determine category-related dissociations. Such traits ('factors') include homomorphy (similarity of form), familiarity, value to perceiver, manipulability, characteristic motion, characteristic sensory modality of transaction (vision, touch, hearing), and typical age of acquisition. It is our view that the mix of factors relative to different conceptual categories plays a key role in the neuroanatomical distribution of records for those different categories, and is thus behind the systematic correlations between certain retrieval defects and damage to certain neural systems [12, 52]. In this study, we operationalized these factors and analyzed their intercorrelations. Stimuli were slides of 215 items from the conceptual categories of animals, fruits/vegetables, tools/utensils, vehicles, and musical instruments. The factors were operationalized on the basis of ratings obtained from 227 normal control subjects and on the basis of computer analyses of the digitized outlines of the stimuli. Principal components analysis revealed that 81% of the variability across items could be accounted for by three components: Component 1 (practically useful, common items): high value to perceiver, tactile mode of transaction, high familiarity, low age of acquisition; Component 2 (homomorphic, non-manipulable items): high homomorphy, low characteristic motion and manipulability; Component 3 (items with characteristic sound): hearing mode of transaction, highly distinctive sounds. In another analysis, we found that the categories of animals versus tools/utensils differed significantly on the factors of homomorphy, familiarity, value, manipulability, characteristic motion, and touch. The factor structure we identified in this study may help explain category-related performance defects in brain-damaged subjects. The results lend support to our proposal that systematic differences in physical characteristics and contextual specification of concrete entities constitute a driving force behind the regionalization of neural systems related to the acquisition and retrieval of conceptual and lexical knowledge.