Optical Illusions

Optical Illusions

1. What is an optical illusion?

   • An optical illusion or also known as a visual illusion is a conflict/paradox between reality and what we perceive
     • An optical illusion tricks you into seeing something else; they an error in our perception of the illusion.
       • The arrangement of depth cues in an illusion result in us perceiving the information and image incorrectly thus seeing ambigious figures, images that are not present, moving images and more; also commonly referred to as illusions.

2. Types of Optical Illusions

   • There are 3 types of visual illusions
     • FIctions
       • A fiction illusion is an illusion caused when a figure is perceived even though it is not present in the stimulus
         • Kanizsa's Triangle: This is an example of a fiction illusion. It is an illusory contour; a boundary, the edge that is perceived in the in a figure but is not present in the stimulus
           • We visualise two triangles yet they are merely lines and and shapes. Our brain fills in the gaps which we then perceive as triangles.
         • Another example of a fiction is a after-effect
           • This is a motion after effect illusion: an llusion caused by paying attention to movement in one direction and perceiving movement in the opposite direction immediately afterwards
           • This however, is a colour- after effect illusion, whereby an illusion is caused by focusing on a coloured stimulus and perceiving opposite colours immediately afterwards
     • Ambiguous Figures
       • An ambiguous figure illusion is when a stimulus with two possible interpretations; which it is only possible to perceive only one of the alternatives at a time
         • Necker Cube: There are two various ways of looking at the cube as you can see from the image
         • Duck/Rabbit Illusion: There are ambiguous figures in this image (the duck, the rabbit) depending on your head positioning, if you look at the image you might see a duck whereas if you tilt you head left you might see a rabbit
         • The Face/Vase Illusion: Some might see two side angled faces whilst other might see a vase however you'll never see them simultaneously making it an ambiguous figure illusion
     • Distortion Illusions
       • A distortion illusion is where our perception is deceived by some aspects of the illusion. This can affect the size orshape of an object. Depth cues such as colour and size constancies are manipulated causing us to distort the image and perceive it incorrectly.
         • Muller Lyer illusion: The two lines are the same length, but the opposing direction of the arrow distorts the image thus we depict it as different lengths.
         • Ponzo Illusion: The two horizontal lines are the same size but the diagonal line distorts the image thus we see otherwise
         • Zollner Illusion: Initially we depict the horizontal lines as not being parallel as the diagonal lines on it (surrounding features) distort the image, however as time progesses and our brain corrects itself we see it as being parrellel

3. An illusion that doesn't fall into any of these categories is the Penrose stairs this is a paradox illusion and is an impossible image as the staircase is depicted as a continuas loop

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