Perceptual segmentations with illusory stratifications were studied by using silhouettes each composed of a circle and a figure having four sharp vertices. The silhouettes were perceptually segmented into the circular areas and the areas with four vertices. Circles are well known as the most typical good figures. We studied whether such a good figure was dominantly perceived as being in front of competitive segmentations. The length of illusory contours is a factor that makes perceptual segmentation difficult. Areas other than common ones in competitive segmentations are factors contributing to perceptual segmentations. The boundary conditions for competitive segmentations in stratification were clarified in terms of both the relative lengths of illusory contours and the relative sizes of areas other than the common ones. Experimental results showed that the areas with the sharp vertices were dominantly perceived as being in front of the circular areas.
