Constancy & Illusions - Georgia Institute of...
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Constancy & Illusions Do You Believe in Magic… April 12, 2020 PSYCH 4041 / 6014
Transcript of Constancy & Illusions - Georgia Institute of...
Constancy & Illusions
Do You Believe in Magic…
April 12, 2020 PSYCH 4041 / 6014
April 12, 2020 PSYCH 4041 / 6014
OverviewØConstancyØIllusionsØUpcoming
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ConstancyØIntro
v Despite great variations, we perceive the world as largely constant
v Heuristics help us simplify our worldv Constancies are the result of several of these
heuristicsv Illusions are often consistencies (or heuristics)
gone wrong
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ConstancyØLightness Constancy
v Lightness of an object appears constant, even in changing lighting• e.g. snow in daylight, snow in shadows, still white• e.g. coal in the sunshine is still black
v Albedo• Proportion of reflected light remains constant
10% 90%
Context is key!!
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Constancy, cont’dØSize Constancy
v Objects of a known size tend to be perceived as unchanged in size when they change distance• e.g. people seen from 5 story building• Note: “within limits”
v Emmert’s LawSize(perceived) = Size(retinal) x Distance(perceived)
v Limits of size constancy• Great distances do not support constancy• Not surprising
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Constancy, cont’dØShape Constancy
v Object is seen to have the same shape, despite different retinal shapes• Other cues provide context (doors, windows, etc.)
v We tend to see objectsand assume depth
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Constancy, cont’dØSummary of Constancy
v Constancy enables perceptual world to correspond to physical world
v Helps us survivev Under some conditions, these (beneficial)
heuristics break downv Result is illusions
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IllusionsØVisual illusions are often the result of
heuristic perceptual processes trying to deal with rare, ambiguous, or contrived stimuli
ØCountless illusions (will see just a few)ØNote that experience is often partly to blame
for illusory perceptionv “garden path”
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Ames IllusionsØTrapezoidal window
v Assumed rectangularityv Actual trapezoidal shapev Assume regular object that
is rotated, rather than irregular object
v Demo:https://www.youtube.com/watch?v=cVepIZLepVc
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Ames Illusions, cont’dØAmes room
v Assume rectilinear room--actually very unusual!
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Ames Illusions, cont’dØAmes room
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Moon IllusionØMoon near horizon appears largerØPossible explanations
v Angle of regard• Eye position relative to body• Not supported by physiology
v Apparent distance• Since perc’d size is proportional to perc’d distance,
then if perc’d distance were greater for the horizon moon it would seem larger
• But… distance paradoxv Others
• e.g. “relative size hypothesis”
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Muller-Lyer IllusionØLines of equal length appear
different, depending on arrow-head contextv Spatial cues “force” depth
interpretation (?)
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Muller-Lyer Illusion
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Ponzo IllusionØPerspective (depth) cues dominate and
cause errors in size judgments
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ØColinear line segments appear misalignedv Perhaps due to assumption
about depth of objectsv Perspective constancy
could explain someexamples of thisillusion (but not all)
Poggendorff Illusion
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Poggendorff IllusionØContext can make it worse (or better)
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Contrast IllusionsØSurrounding objects (context) affects our
judgment of size, alignment, color, etc.
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Contrast IllusionsØA variety of examples
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Contrast Illusions
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Reversible & Multistable ImagesØSome shapes can be seen in multiple
orientationsv Flips may be result of fatigue
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Factors in Illusory PerceptionØOptical and retinal factors
v e.g. subjective curvatureØCognitive components
v e.g. learning, experience, expectation
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Impossible FiguresØCurious…but not really illusory
v We accept them when examined locally, but global inconsistencies are confusing
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Impossible FiguresØEscher is master of impossible figures
v www.mcescher.com
Escher Demo VideosØYouTube:https://www.youtube.com/watch?v=7dMjhhpCQFo
https://www.youtube.com/watch?v=f555rLJnDCI
https://www.youtube.com/watch?v=JdgPvripL9A
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April 12, 2020 PSYCH 4041 / 6014
Summary of IllusionsØNo satisfactory single explanation, in generalØConstancy (of various types) and learning,
expectation, and experience are all major contributors to illusory perceptions at times
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UpcomingØCamouflage
