ABSTRACT
This study investigated the issue of categoryspecific semantic differences with reference to neuropsychological data of patients with semantic dementia. Six patients with mild to moderate semantic impairment were studied. One of the six (patient KH) had presented an emerging category-specific advantage for man-made over living concepts. A battery of neuropsychological tasks was used to compare KH directly with the other semantic dementia patients and to test various accounts of category-specificity. KH demonstrated a consistent domain difference across all semantic tests both for receptive tasks (wordpicture matching and definition-to-picture matching) and expressive tasks (various picture naming tests, and naming to definition). The difference between living and nonliving concepts remained even when other possible confounding factors such as familiarity and frequency were controlled. In contrast, none of the remaining patients exhibited a consistent category-specific difference. A patient would occasionally demonstrate a difference on one test that either was removed when confounding variables were controlled or failed to be replicated with another test even of the same type-e.g., on two picture naming tasks. In other aspects, all six patients, including KH, produced homogeneous results. As in previous investigations of factors that affect semantic performance (Bozeat et al., 2000; Funnell, 1995; Lambon Ralph et al., 1998a), each individual and the group as a whole were affected by concept familiarity. In addition, all patients exhibited a relative preservation of functional over sensory features when asked to provide verbal definitions, name to definition, and match definitions to pictures.
