Investigating the relationship between perceptual categorization and recognition memory through induced profound amnesia

Are perceptual categorization and recognition memory subserved by a single memory system or by separate memory systems? A critical piece of evidence for multiple memory systems is that amnesics can categorize stimuli as well as normals but recognize those same stimuli significantly worse than normals (Knowlton & Squire, 1993). An extreme case is E.P., a profound amnesic who can categorize as well as normals but cannot recognize better than chance. This paper demonstrates that the paradigm used to test E.P. and other amnesics may be fundamentally flawed in that memory may not even be necessary to categorize the test stimuli in their paradigm. We "induced" profound amnesia in normals by telling them they had viewed subliminally presented stimuli that were never actually presented. Without any prior exposure to training stimuli, subjects' recognition performance was completely at chance, as expected, yet their categorization performance was quite good.