Ponzo's illusion (T478/0428) Pillow

Ponzo's illusion. The vertical red line to the left of the image appears to be smaller than the one to the right. In fact they are the same length, but the brain perceives them differently due to the converging black lines. This illusion exploits the brain's understanding of perspective: imagine the converging lines are a representation of a wall going into the distance. The red line to the right then appears to span a greater width of what the brain interprets as parallel lines. Hence it concludes it is larger.