Geometric Illusion Bends the Path of Apparent Motion and Introduction of the Liar-Muller Illusion

Michael K. McBeath

ABSTRACT

This study tests if the path of apparent motion can be bent due to a geometric illusion. The opening experiment uses the path of apparent motion as a test contour to explore if the Hering and Ehrenstein circle illusions are better explained in terms of contour interactions or space deformation. The contour interaction explanationn specifies that distortion is experienced because acute angles appear expanded. If angle expansion occurs, the path of apparent motion should appear to bend in the same direction as test contours in static and kinetic versions of the illusion. In contrast, the space deformation explantion specifies that if a test contour appears straight (as does the path typically favored in apparent motion), it must actually bend in the opposite direction as in static and kinetic versions of the illusion. Results confirmed the prediction of the space deformation explanation. In a following demonstration, apparent motion between alternately presented top and bottom test lines in the Hering illusion produced a "jump rope illusion" that appears as one bent line rotation in depth around the horizontal axis. The findings provide the first reported demonstrations of apparent kinetic geometric illusions, both in the picture plane and in depth. The Liar-Muller illusion is introduced as a kinetic geometric illusions, both in the picture plane and in depth. The Liar-Muller illusion is introduced as a static example in which distortion opposes the contour interaction description of the classic Muller-Lyer illusion.

Figure 2. Experiment 1 Stimulus Conditions		Figure 3. Experiment 1 Results
Figure 4. Experiment 2. Alternately presenting the top and bottom test line-segments appears like either a jump rope rotating out in depth, or a vibrating string deforming the picture plane.		Figure 5. Opposing Illusions The Muller-Lyer illusion (Brentano, 1892) The Liar-Muller illusion (McBeath, 1991)