Müller-Lyer and Oppel-Kundt illusions compared

The modified Muller-Lyer and Oppel-Kundt stimuli possessing three spatial intervals were taken for psychophysical experiments in which subjects adjusted the length of the test interval (the middle one with inward wings or just empty) to be equal perceptually to that of the references (two lateral intervals with outward wings or fillings of spots, line segment, or stripes). The data obtained from thirty subjects showed the two well-known illusions being similar in their manifestation stiles.