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Object recognition under semantic impairment: The effects of conceptual regularities on perceptual decisions.
ROGERS, T.T.R., Lambon Ralph, M.A., HODGES, J.R. & PATTERSON, K.
In Proceedings of the 42nd annual meeting of the Psychonomic Society, Orlando, Florida, November 2001.
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Although patients with semantic deficits can sometimes show fairly good performance on tests of object decision, we present evidence that this pattern applies when nonsense-object stimuli do not respect the regularities of the domain. Eighteen patients with semantic dementia viewed pairs of line drawings, with a real and a chimeric animal side-by-side, and were asked to decide which was real. The chimera was either more prototypical (over-regular condition) or less prototypical (irregular condition) than the real animal. Performance in both conditions was modulated by the extent of the patients' semantic impairment; but regardless of severity, patients were less successful in the over-regular than the irregular condition. The most severe patients were no better than chance on over-regular stimuli, but above 80% correct on irregular stimuli. The results are consistent with a recurrent distributed model of conceptual knowledge, in which structured semantic representations emerge from the interaction of high-level perceptual representations.