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Emmert’s law demonstrates how retinal size is determined by a combination of object size and viewing distance. It’s actually really difficult to guess how far away a visual object is since images close to the eye and far from the eye arrive in the same place in the retina, but as with many other visual problems, our visual system usually solves this easily.

Our brains have learned that retinal size is not an indication of actual object size, so we’re always reaching for other cues to figure out how big something is. The Ames room and Ponzo illusion demonstrate situations in which size perception breaks down because depth cues are strong.

An Ames room is a distorted room used to create an optical illusion of relative sizes (fig.10.12.1). Upon viewing people or objects within an Ames room, there is a loss of normal perspective. As a result of the optical illusion created by the distorted room, a person standing in one corner appears to the observer to be significantly larger than a person standing in the opposite corner while the room appears to be a normal rectangular shape. This is taken to indicate the significant role past experience has on our interpretation of our perceived world.

The Ponzo illusion is an optical illusion where a pair of converging lines distorts the perception of two identically sized lines. Like most visual and perceptual illusions, the Ponzo illusion helps neuroscientists study the way the brain and visual system perceive and interpret images. Artists have also utilized the illusion to great effect in their works.

Learn more about the Ames room illusion by watching this video!