Visual illusions

Overview

Ambiguity, misinterpreted depth cues, fiction and size constancy as explanations, and the Ponzo, Müller-Lyer, Rubin's vase, Ames Room, Kanizsa triangle and Necker cube illusions.

What you need to know

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Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a visual illusion?

   Model answer

   A visual illusion is an image that is perceived differently from how it really is. Illusions show that perception involves interpretation.

2. 2

   How does ambiguity explain some visual illusions?

   Model answer

   An ambiguous figure can be interpreted in more than one way. The brain switches between the possible interpretations but cannot see both at once.

3. 3

   How can misinterpreted depth cues cause a visual illusion?

   Model answer

   A flat image may contain depth cues, such as converging lines. The brain reads these as three-dimensional and misjudges the size or length of what it sees.

4. 4

   What is meant by fiction as an explanation of visual illusions?

   Model answer

   Fiction is when the brain perceives something that is not actually present in the image. The brain fills gaps to create a shape or edge from incomplete information.

5. 5

   How can size constancy lead to a visual illusion?

   Model answer

   The brain automatically enlarges objects it believes are further away. A flat image that fakes distance can therefore make identical objects look different sizes.

6. 6

   Describe the Ponzo illusion.

   Model answer

   The Ponzo illusion shows two identical horizontal lines placed between two lines that converge, like railway tracks. The upper line looks longer than the lower one.

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