The study investigates priming effects in patients with Dementia of the Alzheimer Type (DAT) and Amnesia and relates these effects to perceptual learning ability and memory performance. Priming refers to a variety of phenomena whereby the presentation of one item (the prime) facilitates subsequent processing of either that same item or a different item related to the prime. Thus, priming reflects persistent consequences of perception and therefore represents some form of retention. Priming may be regarded as lying on the interface between perceptual and mnemonic functions and, therefore, allows memory defects to be investigated within a larger context of interacting perceptual and mnemonic processes. This is important in a comparison between relatively pure amnesia and DAT, where memory deficits occur in the setting of more generalized cognitive impairment. The present study will determine the extent and limits of priming in the two patient populations and relate these to theoretical interpretation of the syndromes. Both repetition priming (experiments 1 to 3) and semantic priming (experiments 4.5) will be assessed. Experiment 1 compares priming of items which have well established representations in lexical/semantic memory (real words) to priming of items for which such representations do not exist (nonsense syllables). Experiment 2 directly compares priming and perceptual skill learning and also introduces manipulations which are known to affect priming and recognition memory differently. In experiment 3, pictorial materials are employed, which allows priming of 'literal' representations to be compared to priming of representations at a more abstract level. Experiment 4 is an investigation of semantic priming where prime-target asynchrony (the time difference between the onset of prime and target stimulus) is manipulated such that the time course of semantic priming in the two populations can be determined and compared to that of normal subjects. In the final priming experiment, conditions are introduced where priming produces cost effects such that the relationship between automatic and attentional processes in priming can be determined. All experiments also involve measures of recognition memory.