How Do I See This Illusion?

Upon looking at the image, you will notice that the car on the right appears smaller than the car on the left. When you click on the "Draw Rectangles" button, two rectangles will appear across the brake lights on both cars. You may not believe it at first, but both of these rectangles are the same size! If you're still unconvinced, click the "Animate Shared Rectangle" button. This will move a new rectangle between the two previous rectangles to illustrate how they are the same size.

How Does This Illusion Work?

Our brains percieve distance in terms of perspective. When there's a horizon line that convereges in the distance, our brains understand that things that are farther away are smaller, and things closer are bigger. However, this image throws a wrench into this operation, because both cars are the same size. This non-normal mixing of perspective causes our brains to interpret the distances of the objects in reverse, so now the car father away is bigger than the car that is closer. This is called "inapproprite constancy".

This is a variant of the "Ponzo Illusion". Line B appears to be longer than line A, but in reality, both lines are the same size.