Are living and non-living category-specific deficits causally linked to impaired perceptual or associative knowledge? Evidence from a category-specific double dissociation

Perhaps the most influential view of category-specific deficits is one in which the dissociation between living and non-living kinds reflects differential reliance on, or weighting of visual or associative-functional attributes. We present data collected from two patients, which question the apparent relationship between category-specific deficits and loss of specific attribute types. One patient with dementia of Alzheimer's type presented with relatively poor performance on living things but failed to show a difference between knowledge of visual and associative-functional information. The other patient with semantic dementia demonstrated relatively poor knowledge of visual attributes but failed to exhibit a category-specific impairment for animate kinds. In fact her comprehension and naming were slightly but significantly better for living things. The data are discussed with reference to various theories of category-specific impairment. We suggest that category-specific deficits for living things probably results from a combination of atrophy to medial and neocortical temporal structures, including the inferior temporal lobe. It is proposed that at the behavioural level, category-specific deficits arise when both critical identifying attributes of knowledge are lost and the intercorrelation between features causes disintegration of the category such that each exemplar 'regresses' towards a category prototype.