Perceptual organization in Alzheimer's disease

The ability of 16 AD patients and 16 age-matched control Ss to discriminate degraded forms was compared. Also examined were the effects of aging on perceptual organization by comparison of performance of normal Ss ranging in age from 20 to 86 years. Ss discriminated 2 forms, a circle and a square, each composed of randomly distributed dots concurrently embedded in visual noise. By means of a forced-choice procedure, the threshold signal-to-noise ratios at 4 levels of figure degradation were obtained, each presented at 3 durations. Performance by the normal Ss did not vary with age for long-duration stimuli, but did decline with age for briefly presented stimuli. Relative to age-matched control Ss, AD patients had significantly elevated thresholds at all form densities. Disruption of visual processing at the level of perceptual organization is likely a contributing factor to impairment of high-order visual function.