Although semantic memory impairment is well documented in patients with dementia of the Alzheimer's type, questions remain as to whether the deficit extends to other forms of dementia and whether it differentially affects different domains of knowledge. We examined category naming on two tasks (picture naming and naming-to-description) in patients with Alzheimer's disease (AD: n = 11), Lewy body dementia (DLB: n = 11) and healthy elderly matched controls (n = 22). The DLB and AD groups showed significantly worse naming on both tasks, although the AD patients were more impaired than the DLB patients. Like some AD patients, some DLB patients showed evidence of category-specific naming deficits, and strikingly, all 25 significant category dissociations were for living things. The latter finding accords with the preponderance of living deficits previously documented for AD patients, but extends this finding to DLB patients. The implications of this category bias is discussed in relation to relevant models of category specificity. (JINS, 2007, 13, 401–409.)

Although some studies have reported a category specific naming deficit in Alzheimer's patients (invariably for living things), others have failed to replicate this finding (Laws et al., in press). Inconsistencies may partly stem from the fact that category effects are hidden in group analyses because individual Alzheimer's patients show category deficits in opposing directions, namely, some living and some nonliving (Gonnerman et al., 1997). Additionally, category effects may depend upon the specific composition of living things, such as the ratio of animals to fruits and vegetables, though this has never been explicitly examined. To examine this, we conducted a more detailed fractionation of living and nonliving categories for individual patients.

Humphreys and Forde (H&F) propose that greater within- category structural similarity makes living things more difficult to name. However, recent studies show that normal subjects find it easier to name living than nonliving things when these are matched across category for potential artefacts. Additionally, at the level of single pixels, visual overlap appears to be greater for nonliving things.