An Experimental Examination of the Size-Weight Illusion in Young Children1

Abstract

In a series of investigations of developmental aspects of the sizeweight illusion, almost all 144 Ss, 2 to 10 years, manifested the illusion after being trained to choose the heavier of two cylinders. Frequency of the illusion was unrelated to age, but its magnitude was greater in younger Ss. For 2-year-old Ss trained in finer weight discriminations, magnitude diminished in proportion to skill. The training procedures probably accounted for discrepancies with findings by previous investigators that the illusion increased with age. Present findings are consistent with Piaget's general theory of cognitive development, but not his specific notions concerning the illusion.