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 kn owledge for concrete entities have been well documented in lesion stud ies, and also with functional imaging and electrophysiological approac hes. For example, brain-damaged subjects may be impaired in the abilit y to recognize or to name animals but not tools, or the opposite patte rn may obtain. One reason for these dissociations is that different pa tterns of defects tend to be caused by distinct lesion profiles, sugge sting 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-re lated dissociations. Such traits ('factors') include homomorphy (simil arity of form), familiarity, value to perceiver, manipulability, chara cteristic motion, characteristic sensory modality of transaction (visi on, touch, hearing), and typical age of acquisition. It is our view th at the mix of factors relative to different conceptual categories play s a key role in the neuroanatomical distribution of records for those different categories, and is thus behind the systematic correlations b etween 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 co nceptual categories of animals, fruits/vegetables; tools/utensils, veh icles, and musical instruments. The factors were operationalized on th e basis of ratings obtained from 227 normal control subjects and on th e basis of computer analyses of the digitized outlines of the stimuli. Principal components analysis revealed that 81% of the variability ac ross items could be accounted for by three components: Component 1 (pr actically 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 characteri stic motion and manipulability; Component 3 (items with characteristic sound): hearing mode of transaction, highly distinctive sounds. In an other analysis, we found that the categories of animals versus tools/u tensils differed significantly on the factors of homomorphy, familiari ty, value, manipulability, characteristic motion, and touch. The facto r structure we identified in this study may help explain category-rela ted performance defects in brain-damaged subjects. The results lend su pport to our proposal that systematic differences in physical characte ristics 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. (C ) 1997 Elsevier Science Ltd.