Discovery and a Preliminary Study of the Parallel Lines Illusion Change Effect

The parallel lines illusion change effect (discovered by the authors) was studied: When the plane of a parallel-lines illusion figure intersects obliquely with the line of vision and the figure is rotated, using an imaginary perpendicular line between the parallel lines as the axis, the smaller the intersecting angle, the more the illusory effect decreases, until it disappears. If the illusion figure is rotated and any one of the parallel lines is used as the axis, then the smaller the intersecting angle, the greater the illusory effect. The parallel lines illusion change effect may be applicable to the study of geometric-figure illusions.