A DUCK WITH FOUR LEGS: INVESTIGATING THE STRUCTURE OF CONCEPTUAL KNOWLEDGE USING PICTURE DRAWING IN SEMANTIC DEMENTIA Sasha Bozeat MRC Cognition and Brain Sciences Unit, Cambridge, UK Matthew A. Lambon Ralph Manchester University, UK Kim S. Graham and Karalyn Patterson MRC Cognition and Brain Sciences Unit, Cambridge, UK Helen Wilkin and Josephine Rowland University of Cambridge, UK Timothy T. Rogers MRC Cognition and Brain Sciences Unit, Cambridge, UK John R. Hodges MRC Cognition and Brain Sciences Unit and Addenbrooke’s Hospital, Cambridge, UK In Study 1, six patients with semantic dementia were asked to produce drawings of concrete concepts from dictation of their names. The drawings were characterised by a loss of distinctive features. In the artefact domain, this feature loss resulted in representations that were increasingly box-like. In the living domain, as well as distinctive features being lost, there was a tendency for patients to include incorrect features that resulted in more familiar and “prototypical” representations. A second study included two further conditions in the drawing assessment: immediate and delayed copying of line drawings of concrete concepts. Analysis of the drawings produced by three patients with semantic dementia confirmed that overall performance was significantly influenced by the task condi- tion (immediate>delayed) and severity of disease. The rate of intruding features, but not of omitted ones, was influenced by the domain of the item, with a greater proportion of intrusions in the living than in the nonliving domain. There was also a significant effect of feature distinctiveness on the proportions of these error types: Intruded features were most likely to come from the pool of properties that are shared across domain. INTRODUCTION Semantic memory encompasses our knowledge about objects, facts, and concepts, as well as words and their meaning. The primary aim of this study was to extend previous investigations of the struc- ture and internal representation of visual concep- tual knowledge by analysing the rich database COGNITIVE NEUROPSYCHOLOGY, 2003, 20 (1), 27–47  2003 Psychology Press Ltd http://www.tandf.co.uk/journals/pp/02643294.html DOI:10.1080/02643290244000176 27 Requests for reprints should be addressed to Sasha Bozeat, MRC Cognition and Brain Sciences Unit, Elsworth House, Box 58, Addenbrooke’s Hospital, Cambridge CB2 2EF, UK (Tel: +(0) 1223 355294; Fax: +(0) 1223 359062; Email: sasha.bozeat@mrc-cbu.cam.ac.uk). Q0918–CN5400 / Jan 29, 03 (Wed)/ [21 pages, 7 tables, 7 figures, 1 footnotes] – S endings, c.f. [no comma]. DISK EDITED. Poor quality figures supplied. Figures files output from disk to scan