Visual saltation illusion induced by flashes of subjective contours.

The visual saltation illusion of a Kanizsa-type subjective triangle was demonstrated. After a subjective/real triangle was flashed twice at the same position, another subjective/real triangle was flashed at a displaced position. In a typical case, the second flash was perceived to occur midway between the first and third flash positions. This study showed that the rated illusion strength for the Kanizsa and real triangles largely depended on stimulus onset asynchrony and retinal eccentricity and that the illusion rating was the same between the Kanizsa and real gray triangles when they were presented on black disks (or inducers). When the real triangle was presented in isolation, the illusion rating was lower. Presenting flashes on disks appears to enhance the saltation illusion for both the Kanizsa and real triangles possibly due to a stronger crowding effect or shape changes of inducers enhancing the perception of object appearance and disappearance. Various types of saltation illusions with a Kanizsa triangle are demonstrated in a video.