What are illusions?

What are illusions?

1. a visual illusion is a conflict between reality and what we perceive

2. fiction illusions are caused when a figure is perceived even though it is not present in the stimulus

   • these often involve an illusory contour - a boundary that is perceived in a figure that is not present in the stimulus

3. after-effects are like fictions in the way that they involve perceiving something like movement or a shape that is not in the stimulus, this happens when we look at a stimulus for a long time and then look away

   • a motion after-effect is an illusion caused by paying attention to movement in one direction and perceiving movement in the opposite direction immediately afterwards
   • a colour after-effect is an illusion caused by focusing on a coloured stimulus and perceiving opposite colours immediately afterwards
   • the retina has red, blue and green cones, red and green cones tell us about yellow, these works in pairs, red and green, blue and yellow
     • looking at something red for a long time means the cells that detect red will get tired and the green cells will be more active

4. ambiguous figures are stimuli with 2 possible interpretations, in which it is possible to perceive only one of the alternatives at any time

   • eg. Leeper's Lady and the Necker Cube

5. distortion illusions are where our perception is deceived by some aspect of the stimulus, this can affect the shape or size of an object

   • eg. the Ponzo iIlusion, the Muller-Lyer illusion, the Herring illusion and the Ebbinghaus illusion

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