Optical illusion

Optical illusions and other visual anomalies result from the way the human visual system processes information.

Types of illusion include:

Physical illusions

Physical illusions seem to be hard-wired into the way that the human eye and brain process visual stimuli. Examples include:

  • The Sun and Moon appear much larger when close to the horizon than when high in the sky.
  • Rainbows are composed of a continuous range of wavelengths across the visible spectrum but appear to be formed from bands of colour.
Physiological illusions

Physiological illusions are often connected with the different attributes of visual perception and occur when a visual stimulation is beyond our eyes’/brain’s processing ability. Examples include:

  • The effects of excessive stimulation produced by brightness or hue that result in after-images.
  • Moiré patterns are produced when an area of parallel dark lines with interspersed white spaces is overlaid on another similar pattern that is slightly displaced or rotated.
Cognitive illusions

Cognitive illusions intentionally or accidentally induce ambiguity or confusion about how a visual stimulus should be interpreted. Examples include:

  • Ambiguous illusions are pictures or objects that elicit a perceptual “switch” between alternative interpretations.
  • Distorting or geometrical illusions are characterized by size, length, position or curvature distortions.
  • Paradox illusions are generated by objects that contain visual clues that contradict one another or conflict with deeply embedded ways that we understand the visual world.
  • Fictions are a type of illusion produced when a visual stimulus creates the impression of additional visual content beyond what is present in a scene.