04 - Perception

04 - Perception - Perception Stop moving your eyes and the...

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1 Perception Stop moving your eyes and the illusion disappears. Fixate on the cross-hairs in the center. We can make the movement stop by taking out depth cues. The world may be perceived differently from what reality! Some Questions • Why is perception so complicated? Why do we normally not notice this? • How are objects recognized? • What is the role of knowledge and memory in perception? Perception Overview • is mediated through the senses. – Vision / hearing / smell / taste / touch / balance. • is selective (see „Attention‟). • depends on the environment , the perceiver , and the interaction of both. • involves hypotheses and representations .
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2 Why is perception tricky? Vision is hard as the pattern of light that falls on your retina is consistent with many different scenes. The inverse problem Use Knowledge and Context to resolve An Animal Behind Tree? Or Two Odd Stumps? We make assumptions about how to interpret what we see. Diamond or Square? A Vision Test Read as Quickly as You Can What are these?
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3 The last few example • Were demonstrations of “top down” effects -> the context and our knowledge determine what we perceive. Which is bigger? Object size and distance are indeterminate in a two dimensional representation. The images of the sun and moon seem the same size but they are at different distances and are different sizes. There are Many More Examples How Are Visual Ambiguities Resolved? • The visual system makes assumptions and relies on cues . • Data + Knowledge = Perception Top-down processing Have an idea of what to expect (Knowledge) Match input to expectations So we see what we expect to see Expectations may be built up by context Shape Object orientations are assumed not to be unusual Frame of Reference: The position or orientation of an object is defined relative to something else.
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4 Gestalt’s Law of Perceptual Organization Distance and Size • How can we determine the true size and distance of objects? • Three Cues in the Visual System – Accommodation – lens shape changes as you focus on objects – Convergence – angle of the eyes as you focus on objects – Stereopsis – based on retinal disparity, the difference in position of an object‟s image on each retina Random Dot Stereogram The Hidden 3D Picture Distance and Size - Continued Cues in the Environment Familiar Size Using one’s knowledge of the typical size of an object as a cue to the likely size and distance of an object. For example, if a child appears larger than an adult, it is likely that the child is closer to the observer. Distance and Size - Continued Cues in the Environment Pictorial Cues – Cues to distance that can be used in 2-dimensional pictures : o Occlusion : An object that occludes another is closer o Texture Gradient : A field is assumed to have a uniform texture gradient, so if more detail is visible in part of the field, it is assumed to be closer o Linear Perspective : Parallel lines converge in the
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This note was uploaded on 02/21/2012 for the course PYSC 405 taught by Professor Ferreira during the Fall '11 term at South Carolina.

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04 - Perception - Perception Stop moving your eyes and the...

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