Poster E105, Monday, March 27, 2:30 – 4:30 pm, Pacific Concourse
Rapid visual categorization reveals disrupted ventral stream processing in early Alzheimer’s disease
Leslie Y. Lai1, Elena K. Festa1, Thomas Serre1, Brian R. Ott2, William C. Heindel1; 1Brown University, 2Alpert Medical School of Brown University
Previous studies showed intact performance on standard object perception tests in early Alzheimer’s disease (AD) despite loss of connectivity within the ventral stream. Here we examined whether this disruption produced deficits on rapid categorization tasks imposing high demands on the visual system. Groups of healthy young, healthy elderly, and amnestic mild cognitive impairment (aMCI) patients performed two rapid categorization tasks. Exp.1 used a go/no-go task in which participants pressed a button as quickly as possible whenever an image contained an animal. Stimulus duration was adjusted on no-mask trials to equate performance across subjects using a staircase procedure, and a mask followed each image (SOA range: 21ms–63ms) on all remaining trials. Exp.2 used a forced-choice saccadic task in which participants were shown two images simultaneously, and made saccades as quickly as possible toward the image containing an animal. In Exp.1, young and elderly controls performed above chance on mask and no-mask trials (no-mask better than mask), with aMCI patients impaired only under masked conditions. In Exp.2, all groups performed better on trials with highly discriminable distractors. While performance also improved on trials with longer saccade latencies allowing greater recurrent processing, aMCI patients showed less improvement with low discriminable distractors. Results suggest that visual ventral stream processing is preserved in normal aging, but that aMCI patients’ performance may reflect subtle disruptions of cortico-cortical projections associated with preclinical AD. These findings serve as a critical first step in the development of a sensitive tool for early detection of neurocognitive changes in AD.
Topic Area: PERCEPTION & ACTION: Development & aging