Authors:

BARENSE, M.D., Bussey, T.J., LEE, A.C.H., ROGERS, T.T., HODGES, J.R., Saksida, L.M., Murray, E.A. & GRAHAM, K.S.

Reference:

Year of publication:

2005

CBU number:

6091

Abstract:

Recent studies suggest that the perirhinal cortex may be involved in the perceptual discrimination of complex objects with a large number of overlapping features. To test this view, the performance of a group of semantic dementia (SD) patients, who have asymmetric focal atrophy to the anterolateral temporal lobe, including perirhinal cortex, was assessed on concurrent object discriminations similar to those used in monkeys (Bussey et al, 2002). Subjects learned a series of discriminations between objects with varying levels of perceptual overlap: (a) maximum feature ambiguity, in which all features were ambiguous (i.e., both rewarded and not rewarded); (b) intermediate feature ambiguity, in which half of the features were ambiguous; and (c) minimum feature ambiguity, in which no object features were explicitly ambiguous. Across conditions we manipulated the familiarity of stimuli: two ‘novel’ tasks in which stimuli were completely unknown (blobs and barcodes), and two ‘familiar’ tasks in which stimuli were comprised of meaningful features (bugs) and meaningful concepts (animals). As predicted, SD patients performed normally on all minimum feature ambiguity conditions. The patients were severely impaired, however, on the intermediate and maximum feature ambiguity conditions of bugs and animals, but showed equivalent performance to controls on all novel stimulus items (blobs and barcodes). These results are consistent with findings in patients with nonprogressive lesions to the MTL, including perirhinal cortex. In addition, they highlight the role played by semantic memory in perceptual discrimination. Funded by the Medical Research Council, UK and Alzheimer’s Research Trust, UK.