Abstract
The anisotropy of angle illusion is already established. If the Muller-Lyer illusion is caused by angle illusion, it should be possible to observe the anisotropy of the Muller-Lyer illusion. The apparent length of the shaft lines of the Muller-Lyer figures (obliques-in, H-shape, and obliques-out figures) and the control figure, were estimated by twenty-two university students, when the orientation of each figure was varied in eight steps: 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5° counterclockwise from the horizontal. The anisotropy of the apparent length of the shaft line of each figure was observed, and these regression curves became quadratic functions. But the anisotropy of the Muller-Lyer illusion was not observed. It was concluded that the relationship between angle illusion theory and the Muller-Lyer illusion was doubtful.
