Brain, Vol. 115, No. 3, 711-733, 1992
© 1992 Guarantors of Brain
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VISUOSPATIAL ATTENTION IN DEMENTIA OF THE ALZHEIMER TYPE
1Cognitive Science Laboratory and Department of Psychology, The Catholic University of America Washington, DC 2Laboratory of Neurosciences, National Institute on Aging Bethesda, MD, USA
Correspondence to:
Correspondence to: Raja Parasuraman, Department of Psychology, The Catholic University of America, Washington, DC 20064, USA.
Cue-directed shifts of spatial attention were examined for a letter-discrimination task in 15 patients with mild to moderate dementia of the Alzheimer type (DAT) and 15 healthy, age-matched controls. Spatial cues were valid, invalid or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7° to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200 ms and 2000 ms. Reaction time (RT) benefits conferred by valid cues did not differ between the DAT group and the controls. However, RT costs incurred by invalid cues were significantly greater in the DAT group than in the control group. Group differences in RT costs plus benefits occurred at short SOAs (<500 ms) for peripheral cues and at long SOAs (>500 ms) for central cues. Reaction time costs plus benefits were correlated with right-left asymmetry in resting levels of cerebral glucose metabolism in the superior parietal lobe for DAT patients but not for controls. The results indicate that focusing of attention to spatial location is intact in early DAT, whereas the disengagement of visuospatial attention is impaired. Automatic attention shifts elicited by peripheral cues reveal abnormalities earlier than attention shifts initiated ‘effortfully’ by central cues. Intact focusing and impaired disengagement of visuospatial attention may be linked to dysfunction in early DAT of cortico-cortical networks linking the posterior parietal and frontal lobes.
Received January 25, 1991. Revised October 30, 1991. Accepted February 2, 1992.
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