Effect of orientation on judgments of line length.

This study investigated how the parameters of the power function of line judgments by 68 college undergraduates were affected by orientation of line. Exponents of the power functions did not vary as a function of orientation, but the scaling factors varied substantially. These results suggest that the horizontal-vertical illusion is best described as about a 12% illusion. Also, results are inconsistent with the hypothesis that the horizontal-vertical illusion affects the exponent of power functions for judgments of area and volume.