Hering illusion, illustration. This illusion was created by the physiologist Edward Hering in the 19th century. It exploits the brain's understanding of perspective to fool it into thinking that the two horizontal lines bow outwards. In fact they are straight and parallel. This is achieved due to the presence of the grey lines radiating from a point. They give the illusion of depth. In this 2D representation of 3D space a straight line would be drawn curving slightly inwards, since the part in the middle seems lower than that at the side. So, similarly, a straight line in 2D space represents a slight outwards curve in 3D space.