Neon colour spreading in three-dimensional illusory objects in humans

We studied whether neon spreading can be induced within three-dimensional i llusory triangles. Kanizsa triangles were induced by black pacman disks con sisting of red sectors with curved sides. Viewing our stimuli monocularly p roduced two-dimensional illusory contours and surfaces as well as neon spre ading in each figure. Triangles appeared concave or convex under stereoscop ical viewing. Neon colour spreading was induced within illusory figures ben ding in three-dimensional space, suggesting that neural contour completion and surface filling-in interact across depth. Surprisingly, neon spreading was induced above the intervening surface even when the inducers were below the surface. Neon colour and illusory configuration were preserved behind the intervening surface only when it appeared transparent, (C) 2000 Elsevie r Science Ireland Ltd. All rights reserved.