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The role of constancy in the perception of illusion.

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The role of constancy in the perception of illusion. Perceptual constancy is the sensory information we receive from the environment around us. It is constantly changing around us yet we still see objects as relatively stable and unchanging despite these changes. Our brain applies perceptual constancies to see the world around us accurately, for example, when we look at something in the world around us, our brain picks out cues from the surrounding environment to enable it to make judgment about the distance an object is away from us. The brain applies size constancy (scale it up) to be able to perceive the size accurately. Cues in the environment enable us to accurately perceive size and depth. Visual illusions are specially designed 2D images, which are designed to make us misinterpret the 3D cues so that we see a 3D image for example Figure 1. ...read more.


However not everyone can see the illusion. The Zulu Tribes of Africa live in a very small insular environment. They are born, grow up, work and die within a tiny radius, so they have little or no linear perspective, the world they live in is small and round. This means their interpretations of the Muller-Lyer illusion in Figure 2. is not the same as your or my interpretation their visual past experience has not allowed their depth perception to develop in the same way as our has. Visual illusions are designed to have depth cues. As a result due to having lived in an environment that's rich in depth cues, we perceive these depth cues, apply size constancy and perceive the illusion. When we are in a familiar situation we expect to see or hear something based on our past experience of that situation. ...read more.


One way to illustrate this is to adapt the Muller-Lyer illusion by taking away the fins and replacing them with circles as shown in Figure 3. Figure 3. We have manipulated the illusion by taking away the depth cues, but our brain uses past knowledge and experience and still perceives the illusion. Line A still looks shorter than B even with the replacement of the fins with circles. In conclusion, research using visual illusions has led to knowledge of how depth cues cause 3D perception and how our brains apply perceptual constancies. Our past experience and expectations affect the way we see ambiguous drawings!1 1 Gregory's (1972) Top-Down Theory - The top-down process involves the brain 'sending down' stored information to the sensory system as it receives information from the stimulus, enabling a plausible hypothesis about the scene to be made without the need to analyse every feature of the stimulus. 2 Muller-Lyer illusion (1972) - an illusion to show perception, involving two lines the same size with different depth cues. ?? ?? ?? ?? ...read more.

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