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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