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Sources of Illusions

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Sources of Illusions

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    1. Sources of Illusions Illusions occur because our perceptual system is structured to function as though our assumptions and hypotheses about the world around us are true. In situations where our assumptions appear to be true but are actually not, we automatically construct perceptions that bring some sense of meaning and order. These misperceptions are called illusions. Then we realize that there are alternative, incompatible, and equally valid perceptions in addition to the one we constructed.

    2. Visual Perception & Illusions

    3. Dark Adaptation Rods & cones contain photopigments Photopigments are bleached or burned out by light They eventually regenerate However, if you stare at a bright light such as the sun for long enough, some will burn out permanently Cones regenerate quicker (10 min) than rods (about 30 min) Eyes adapted to the dark are 100,000 times more sensitive to light.

    4. Gestalt Theory of Perception We impose order and structure on what we see. Our expectancies affect how we interpret sensory input. Hence, Gestalt is a top-down theory of perception.

    6. Figure-Ground Differentiation Major Gestalt principle of perceptual organization We divide world into 2 parts Figure Has shape & location in space Ground Has no definite shape and seems to continue beyond figure

    7. Bill or Monica?

    8. Find the Hidden Star

    9. Gestalt Laws of Perceptual Grouping – Top-Down How do we group objects perceptually? Several principles: Similarity Proximity Continuation Simplicity Closure

    10. Similarity

    11. Proximity

    12. Continuation

    13. Simplicity

    14. Closure

    15. Perceptual Constancies Does our perception of objects around you change if objects get closer or farther away, or if they are moving? No! No! No! No! No! No! No! Why? Because of perceptual constancies

    16. Size Constancy

    17. What happens when our perception fails? Illusions (incorrect perceptions) 2 major categories: Illusions of size size constancy at work (e.g., St. Louis Gateway, Ponzo Illusions) – objects higher in our visual field are perceived as more distant learning and past experience (e.g., Muller-Lyer illusion) Illusions of shape

    18. Distance and depth perception How do we judge distance and depth? We utilize a variety of cues!

    19. Ponzo Illusion: line in the distance appears larger

    22. Muller-Lyer illusion: which line is longer?

    25. Illusions of shape: the Moon illusion

    26. Just plain cool illusions!

    27. All lines below are straight; distorted pattern created by the tiny squares

    28. Café wall illusion

    33. Click here to go to a website about motion perception Motion sensing four-stroke motion motion aftereffect RDKs second-order motion 2-D integration motion capture direction repulsion plaid motion

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