Color, Depth, and Size

106 Size Illusions

Learning Objectives

Understand the concept of retinal size and why it is not reliable for perceiving size.

Be able to give at least 2 examples where size perception strongly relies on depth cues (e.g. Ponzo illusion).

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.

Fig.10.12.1. Ames room. This is an example of how a distorted room creates an optical illusion. (Provided by: The New World Encyclopedia. License: CC-BY-SA. )

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



New world encyclopedia, Ames Room
License of original source: CC-BY-SA 3.0

New world encyclopedia, Ponzo illusion
License of original source: CC-BY-SA 3.0

Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
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License of original source: CC Attribution 4.0


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Introduction to Sensation and Perception Copyright © 2022 by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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