Exhaustive neuropsychological assessment of mild cognitive impairment (MCI) subjects frequently identifies cognitive deficits other than memory. However, visuoperception has rarely been investigated in MCI. The 15-Objects Test (15-OT), a visual discrimination task based on the Poppelreuter Test, consists of 15 overlapping objects. Poppelreuter-type tests are frequently used to detect visual agnosia. However, more complex tests, such as the 15-OT, are required to detect visuoperceptual signs in those patients who perform correctly on simple tests. The aim of the present study was to investigate visuoperceptual deficits in MCI patients and to assess the usefulness of the 15-OT to discriminate Alzheimer's disease (AD) and MCI patients from controls. The 15-OT, and a neuropsychological battery included in the diagnostic assessment, was administered to 44 healthy controls, 44 MCI patients, and 44 mild AD patients. Performance on the 15-OT was significantly different between groups. MCI scored between AD and controls. When MCI and AD patients had relatively normal performance on simple tests (Poppelreuter), increased significant abnormalities were found by a more difficult visuoperceptual test (15-OT). Regression analyses showed that the 15-OT was a significant predictor of group membership, but the Poppelreuter Test did not significantly contribute to the models. Visuoperceptual processing is impaired early in the clinical course of AD. The 15-OT allows detection of visuoperceptual deficits in the preclinical and mild AD stages, when classical tests are still unable to detect subtle deficits. So, its inclusion in neuropsychological batteries that are nowadays used in the clinical practice would allow increasing their diagnostic potential.
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