Hemispheric asymmetry in a perceptual priming task: evidence from patients with unilateral brain damage

Disappearance of memory fragments in patients with Alzheimer's disease: evidence from a longitudinal study of visual priming

Previous studies suggested that perceptual memory as indexed by visual priming is normal in patients with Alzheimer's disease (AD). However, these studies did not specifically test the long-term effects of visual priming, which may differ significantly between Alzheimer's patients and normal subjects. To test this possibility, we examined long-term visual priming in AD patients, 1 hour, 1 month, and 3 months after training. Our results indicated a significant difference in visual priming between AD patients and normal subjects after 3 months, but not 1 month. For AD patients, there was a strong positive correlation between the 3-month priming effect and the Mini-Mental State Examination (MMSE) scores-severely demented patients were less likely to exhibit priming after 3 months. It appears that severe cortical degeneration may render AD patients unable to consolidate their perceptual memories. Our results suggest that lack of visual priming in AD patients is linked to the inability to maintain fragmented perceptual memories.

Lateral asymmetries in attentional priming during a semantic and a visuospatial task

This study tests the hypothesis that lateral cueing of attention activates the contralateral hemisphere and also that performance on a semantic and a visuospatial task will differentially be affected depending on the visual field (right or left) to which attention was drawn. In an experimental setting, 68 subjects performed both a semantic and a visuospatial discriminating task, whereby visual priming signals unbeknownst were presented to either the left or the right visual field. For the semantic task (which is believed to engage primarily the left hemisphere) priming signals enhanced performance more when they were presented to the right visual field. For the visuospatial task, no difference was found between priming signals presented in either visual field. While there may be several alternative explanations for the observed difference in the effects of the priming signals presented to different visual fields, the importance of separating the components inherent in the tasks is stressed. While the process of decision-making may involve different relative activation of the two hemispheres, depending on whether the stimuli are semantic or visuospatial in nature, performance on the task also involves manual coordination which will depend especially on motor activation in the left hemisphere.