Question

The following image shows an illusion, named the Ponzo illusion. What is the illusion? What might account for the illusion? Use the size distance scaling equation (S = R * D) to explain why the top horizontal line looks longer. (Only answer this question after you have done the reading and gone through the powerpoint lecture).

Answer 1

PONZO ILLUSION Ponzo illusion is an optical illusion where a pair of converging lines distorts the perception of two identical sized lines. The ponzo illusion helps neuroscientists study the way the brain and visual system perceive and interpretimages. The ponzo illusion is often illustrated with two converging lines that mimic railroad tracks disappearing into the distance. The two horizontal lines or bars are placed across these tracks, one higher than the other, when looking at the image, viewers see the upper bar as larger than the lower bar, in reality the two bars are identical size. Size distance scaling The size distance scaling refers to an idea that the perceiver combines the size of an object formed on retina and its distance to perceive the actual size of the object. The perception of size depends closely on our perception of depth. If the size of an object in retinal image be R, the depth of the object be D and the focal length of eye, the perceived size Sis related to these by similar triangle equation.

SERXD Sis the perceived size, R is the retinal image size, D is the perceived distance After image on wall After image on back Retinal image on circle If you keep the retinal image size constant, changing the perceived distance should change the perceived size.

The effect of ponzo illusion is often attributed to linear perspective. The upper line looks longer because we interpret the converging sides as parallel lines receding into the distance. In this context we interpret the upper line as though it were farther away, so we see it as longer. The framing effect, where objects that appear to fill an enclosing border appear larger than the same object surrounded by a large frame, also contributes to the illusion. The difference in the separation or gap of the horizontal line from the framing converging lines helps to create the sense that the upper bar, which is closer to the bordering lines, is larger than the lower one.