Assuming a particular psychological function of optical gestalt perception,
its impairment would lead to a decreasing extent of gestalt related optica
l illusion. An increase of optical illusion would be expected in the case o
f a loss of adaptability and cognitive compensation, usually revising the p
henomenon of optical illusion. 16 demented out-patients were compared to 16
hospitalized schizophrenics by a 'Computerized Assessment of Change in Opt
ical Illusion' (CACOI), measuring the extent of optical illusion by patient
's assessment of 12 variations of the figure of Mueller-Lyer, differing in
baseline length. The results showed a significant increase of optical illus
ion in demented patients compared to the schizophrenic controls (p = 0.019)
. Taking into account that the extent of optical illusion by the figure of
Mueller-Lyer usually is decreasing with age and was found to be increased i
n schizophrenics, our results support the hypothesis of an early loss of ad
aptability and cognitive compensation in dementia.