A MOTION ILLUSION FROM 2-DIMENSIONAL PERIODIC PATTERNS

The spatial properties of a motion illusion (the Ouchi illusion) that occurs in a stationary pattern were examined by means of a variety of two-dimensional periodic patterns (formed by multiplying pairs of vari ous one-dimensional periodic functions). In two experiments, observers rated the magnitude of the illusion. The results showed that (1) patt erns having large energy and steep saddle-shaped contrast gradients te nded to generate stronger illusions, (2) the composite pattern made up of the sum of the fundamental and harmonic components exhibited a str onger illusion than either the fundamental or the harmonic pattern, (3 ) patterns possessing an element orientation and phase shift similar t o those of a rectangular checkerboard, and with element sizes of 15-50 min in width and 4-8 min in height yielded a larger illusion, (4) equ iluminant colors largely abolished the effect, and (5) blurring the bo undary between the test and surround did not reduce the illusion. Inte ractions between spatially overlapping ON and OFF units was discussed as a possible underlying cause of this phenomenon.