Ponzo's illusion. The figure of a man to the left of the image appears to be shorter than the one to the right. In fact they are the same height, but the brain perceives them differently due to the converging black lines. This illusion exploits the brain's understanding of perspective representation of a wall going into the distance. The man to the right then appears to span a greater height of what the brain interprets as parallel lines. Hence it concludes he is taller.