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Sensation & Perception
Ch. 10: Perceiving depth and size
© Takashi Yamauchi (Dept. of Psychology, Texas A&M University)
Main topics
Monocular depth cues
Binocular depth cues
Visual illusion
The physiology of depth perception
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Tell me why these pictures look bizarre?
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Escher:
Ascending
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Belvedere: Escher
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Red Ants: Escher
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Relativity: Escher
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Up and Down: Escher
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Waterfall: Escher
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ch 10 10De Chirico
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Why do these paintings evoke a strange feeling?
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Leonardo da Vinci (1452-1519)There has never been an artist who was more fittingly, and without qualification, described as a genius. Like Shakespeare, Leonardo were from an insignificant background and rose to universal acclaim. Leonardo was the illegitimate son of a local lawyer in the small town of Vinci in the Tuscan region….
Mona Lisa (1503)
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The Dreyfus Madonna: da Vinci 1469
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Why did Leonardo become so famous?
One secret:
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The Last Supper: da Vinci, 1498
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The virgin of the rocks: da Vinci, 1483-1486
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Madonna Litta: (da Vinci)
1490-1491
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The Santa Trinita Madonna: Cimabue (1260/80)
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Coronation of the virgin altarpiece from San Domenico: Fra Angelico, 1434
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The presentation of the virgin: Giotto, 1305
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Madonna in Glory: Giotto, 1311
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Why did Leonardo become so famous?
• Or what made Leonardo’s pictures so special?
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1469
1260/801311 1434
2000
Historical depiction of Madonna
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1469
1260/801311 1434
2000
Historical depiction of Madonna
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What I think:
• Everything before Leonardo was very flat.
• These pictures were so crisp clear.
• No ambiguity.
• Leonardo (A-rod) made things more ambiguous.
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Leonardo found two tricks
• To depict distance, L used (but not W, definitely not A-rod)
– Linear perspective– Atmospheric perspective
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Leonardo used lots of pictorial cues to depict depth
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Atmospheric perspective
Things get vague when they are away.
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Things get smaller when they are away.
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Linear perspective
Things get smaller when they are away.
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Linear perspective
• Linear perspective is very “Renaissance.”
• Renaissance humanism free from feudalism (religious bigotry)
• Put a person at the center of the world.– Not religious authority
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Other quintessential Renaissance men are
• Descartes (1590-1650)– I think therefore I am. (“I” is the center).
• Linear perspective is a pictorial version of “I think therefore I am.” (my idiosyncratic interpretation).
• Why?
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• Linear perspective is about putting yourself at the center of the physical world.
• and arrange everything else based on that center.
• It is about reproducing the relationship between you, the painter, and the other objects in the world in pictorial space.
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Monocular pictorial cues
• Occlusion
• Relative height
• Relative size
• Familiar size
• Atmospheric perspective
• Linear perspective
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Occlusion
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Relative height
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Relative size
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Atmospheric perspective
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Texture gradient
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• These cues are something you notice everyday in the physical world.
• The visual system uses these cues and generates depth perception naturally. – You don’t need to think about them. They are
just there.
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Visual Illusions
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(A)
(B)
(A)
(B)
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Tell me why these pictures bizarre?
• Any idea?
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What makes these pictures surreal?
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What makes these pictures surreal?
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Any idea?
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My guess:
• These pictures deliberately violate pictorial cues. which evokes a strange feeling. these pictures depict impossible scenes by
reversing depth relations.
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• Violating some depth cues– Deliberately introducing contradictory depth information.
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What makes these pictures surreal?
Violating linear perspective
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How to make an Escher figure.
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Other cues
• Movement parallax– Nearby objects move faster than distant objects– http://video.google.com/videoplay?docid=-
5983729407150064898&q=motion+parallax&total=43&start=0&num=10&so=0&type=search&plindex=2
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Visual Illusions
• http://users.skynet.be/J.Beever/pave.htm
• http://www.magiceye.com/
• Ames room (1:13)– http://www.youtube.com/watch?v=Ttd0YjXF0
no&feature=related
• Star wars: Attack of the clones (10 min)– http://www.youtube.com/watch?
v=3VEdD8QOlGk
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http://www.greatbuildings.com/buildings/Guggenheim_Bilbao.html
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Binocular Depth Information
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Why do we have two eyes?
• Long, long time ago, we used to have one eye or no eye at all.
• Now we have two eyes.
• How come?
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Before
I guess we were all like these.
Now
We got two eyes. How come?
And then
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Something to do with evolution?
• Some kind of evolutionary force
• Having two eyes is evolutionarily advantageous?
• What advantage is it?
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What eyes are for?
– The eye is a sensor.
– It is about detecting things in the world.
– Eyes used to be part of “skin.”
– some part of skin (cell body, membrane) became particularly sensitive to light.
– And eventually that part developed to possess eye-like functions.
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We got two ears, two nostrils as well.
• The same thing is true for ears, and probably for nostrils, too. – But not for the mouth.
• Two eyes, two ears, and two nostrils help the organism to locate things in the 3-D world
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Binocular depth cues
• Ever visited an IMAX theater?
• Or some special planetarium?– Wearing special sunglasses and see a large
screen.– You get an incredible 3-D effect.
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Binocular disparity& Binocular depth cues
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DemoStep 1: Hold your one finger about 8 inches in
front of you and the other about 15 inches in front of you.
Step 2: Focus on the one that is further from you, and move the other finger back and forth.
Got double images for the unfocused finger? But why?
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Binocular disparity• Your two eyes are getting
different images disparity double images
Corresponding points
Corresponding points
No disparity disparity
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Small disparity
Large disparity No disparity
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Horopter (Vieth-Muller circle)
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Binocular disparity
• The binocular disparity arises when a given point in the external world does not project to the corresponding points on the left and right retinae – (Palmer, 1999, “Vision Science”)
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Binocular disparity
- OK, then open your right eye and close your left eye. What happens? Repeat this several times.
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Binocular disparity
- OK, then open your right eye and close your left eye. What happens? Repeat this several times.
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• Do the same thing several times.
• This time change the distance between your focused and unfocused fingers.
– When your unfocused finger is close to you, – That finger moves further left.
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• Your unfocused finger moves to the left. • Why?
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Small disparitylarge disparity
small
distance
large
distance
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Binocular disparity
• The amount of disparity can tell us how far an object is apart from the object you are focusing on.
• But how do we know the unfocused objects is farther from or closer to you?
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2 types of disparity
P
F
P
C
crossed disparity
uncrossed disparity
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• P falls on the foveae of both eyes, so they stimulate corresponding points.
• Both F and C do not fall on the corresponding points.
• C is close, and the disparity goes outward. “Crossed disparity”
• F is farther, and the disparity goes inward. “uncrossed disparity”
• These two types of disparity signals the brain whether the object is close to or far from you.
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Where?
• Binocular depth cue you need two eyes
• V1 (striate cortex is the first location where the information from the two eyes is merged).
• Specific neurons in V1, V2 and V3 respond to disparity.
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Emmert’s law
• S = R x D
– S: Perceived size– R: retinal image– D: perceived distance
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Fig. 10-33, p. 248
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