The semantic memory impairment of Alzheimer's disease: category-specific?

We addressed the question of whether Alzheimer's Disease (AD) causes a selective impairment for knowledge of living things. Although we replicated a previous finding that AD subjects name pictures of living things less accurately than pictures of nonliving things, we also failed to observe this selective impairment when we used two new stimulus sets, which more tightly controlled the overall naming difficulty of the living and nonliving items. We conclude that, whereas some individuals may have bona fide selective impairments in semantic memory as a result of herpes simplex encephalitis or head injury, AD does not generally give rise to selective impairments in knowledge of living things.