Abstract: Measurements in Müller-Lyer illusion were taken in adults as well as subjects ranging ,sexdifferencefrom 6 to 18 years of age. The results indicated that: (1) The illusion shows no sex difference, but changes with different age levels, it decreases from 6—16 years of age; (2) Involvement of the thought process decreases the illusion; (3) Adults with different professional experiences showed some differences in the illusion.

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