Perception puzzles, Visual Perception, Optical illusions and Paradoxes. This page illustrates that our visual perception cannot always be trusted.
The components of an object can distort the perception of the complete object. Our mind is the final arbiter of truth. Most optical illusions are the result of 1) incongruent design elements at opposite ends of parallel lines, 2) influence of background patterns on the overall design, 3) adjustment of our perception at the boundaries of areas of high contrast, 4) afterimages resulting from eye movements or from kinetic displays, or 5) inability to interpret the spatial structure of an object from the context provided by the picture.
The Parthenon. Color Survey Results « xkcd. Who in the rainbow can draw the line where the violet tint ends and the orange tint begins?
Distinctly we see the difference of the colors, but where exactly does the one first blendingly enter into the other? So with sanity and insanity. MRC CBU, Cambridge » Matt Davis.