Category-specific visual identification of filtered objects in Alzheimer's disease.

The category-specific deficit in object identification as function of spatial frequency (SF) content and priming effect was investigated. Twenty-two patients with Alzheimer Disease (AD) and 24 control subjects performed an object identification task. The objects belonged to living and nonliving categories. In the study phase an episodic trace of objects was created. In the identification phase, each object was revealed in a sequence of frames wherein the object was represented by an increasingly less and less filtered image up to complete version. A recall phase followed immediately after the identification phase. While the priming was preserved in mild-AD but not in moderate-AD, no difference was observed in the recall task. Moreover, although patients showed a decline in performance for both categories compared to controls, this decline was more rapid for living things especially in patients with more severe disease. Present results indicate a semantic memory deficit along with a disruption of perceptual representation. Data were discussed referring to perceptual/functional, domain-specific knowledge, and prefrontal cortex (PFC) theories.