This makes a specific prediction: interspersing discriminations of visually dissimilar objects between the high ambiguity discriminations should reduce interference in the ventral visual stream and restore perceptual ability. Barense et al. (2012) retested their amnesic subjects with blocks of discrimination problems configured to induce high or low degrees of interference between high ambiguity discrimination problems (Figure 1) to test this prediction. They found precisely the expected result: perceptual performance in the MTL amnesics deteriorated in the high interference

PLX-4720 chemical structure block but was normal in the low interference blocks given before and after. This remarkable finding shows that experimentally reducing interference recovers patient

performance to normal levels. Therefore, intact memory for irrelevant, lower-level features processed on previous trials can learn more impair perception in individuals with memory disorders. This supports the representational-hierarchical view, that representations for memory and perception are shared and are especially critical when the capacity of lower-level ventral visual stream regions is exceeded by repeating features. Moreover, the finding that intact visual memory impairs visual perception in individuals with MTL amnesia is fundamentally incompatible with the notion of a specialized MTL memory system. This view does not allow for the presence of visual, declarative memories outside of the MTL, whereas the current findings clearly show that such memories are present and can interfere with perceptual processes that depend on structures located within the MTL. The notion that overload of ventral visual stream structures with interfering

information gives rise to perceptual, and perhaps memory (McTighe et al., 2010), impairments in amnesia has some intriguing implications for cognitive rehabilitation. For instance, individuals with amnesia may function better in environments next that are designed to reduce interfering sensory information. The effects of environmental features, including “sensory comprehension,” which includes meaningful and discriminable sensory input, on behavioral outcomes in patients in Alzheimer’s special care units has been reported (Zeisel et al., 2003). The present data suggest a mechanism by which environmental design may enhance the ability of these individuals to function effectively. An as yet unanswered question concerns the nature of the memory deficits in individuals with selective hippocampal damage, who discriminate high ambiguity objects normally even under high interference conditions and yet still have severe amnesia. The resolution of this question will require further research, but the representational-hierarchical view posits that the function of the hippocampus can be understood in the same context as that of the perirhinal cortex.