Importance of relative width differences and instructions on shape constancy performance.

Adult subjects were instructed to select either the wider physical or the wider perspective shape of two rotated rectangles. With equal differences between the physical and perspective widths, responses were governed by instructions and by the magnitude of the differences between widths of the forms. However, with unequal differences between physical and perspective widths of the two rectangles, responses were governed primarily by the magnitude of the differences. Regardless of instructions, responses were to the dimension with the greater difference between widths. The results suggest that performance in the shape constancy experiment is a function of relative dimensional discriminability, as defined by instructions, and relative differences of widths between forms presented for comparison.