Abstract
Changes in magnitude of Muller-Lyer illusion as a function of age were studied in 48 hyperactive and 48 nonhyperactive boys. As expected, a decreasing linear trend in magnitude of illusion was found with increasing age from 6 to 9 years for nonhyperactive boys. For hyperactive boys, illusion increased from 6 to 7 years and then decreased. Differences in illusion with age for hyperactives resembled Piaget's hypothesized developmental curve for primary illusion moved forward in years, supporting the notion of a lag rather than an aberrancy in perceptual development. Peak illusion was found for 6-year-old non-hyperactives and 7-year-old hyperactives. By ages 8 and 9, no significant differences were found between the two groups.
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