Abstract
Op artist Hajime Ouchi's book on “Japanese Optical and Geometrical Art”, first published in 1973, featured a striking motion illusion in which a black-and-white checkered disk appeared to float and shift against a checkered background (1). The illusion languished in obscurity until vision scientist Lothar Spillmann stumbled upon it and introduced it to the vision research community (2), where it has enjoyed enormous popularity. Here we report a novel variant of the Ouchi-Spillmann illusion. Whereas in the classical version the disk pattern has an opposite orientation to that of the background, the new illusion consists of a single checkered pattern with an overlaid solid ring (that is either black or white). The ring's position becomes unstable upon observation, shifting from side to side if the checkered pattern is horizontal (i.e. in its longest orientation axis), or moving up and down if the checkered pattern is vertical. The strength of the illusion is enhanced for patterns made with elongated checks, and diminished for patterns with more symmetrical (i.e. square) checks. As in the classical Ouchi-Spillmann's illusion, the observer's head and eyes movements appear to facilitate the perception of motion. We propose that the original Ouchi-Spillmann illusion and the novel variant reported here are modulated by the observer's exploratory and fixational eye movements, including both saccades and microsaccades. Further, the illusory motion in the new variant may result from eye position changes along the same axis as the perceived direction of motion. (1) Ouchi H (1977) Japanese Optical and Geometrical Art. Dover, New York. (2) Spillmann L, Heitger F, Schuller S (1986) Apparent displacement and phase unlocking in checker-board patterns. 9th European Conference on Visual Perception, Bad Nauheim.
Barrow Neurological Foundation (to SMC and SLM) and National Science Foundation (awards 0643306 and 0852636 to SMC). JOM is a fellow of the Barrié de la Maza Foundation.