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 ch 10 1

Tell me why these pictures look bizarre?
ch 10 2

Escher:
Ascending ch 10 3

Belvedere
: Escher ch 10 4

Red Ants:
Escher ch 10 5

Relativity:
Escher ch 10 6

Up and Down:
Escher ch 10 7

Waterfall:
Escher ch 10 8

ch 10 9

De Chirico ch 10 10

Why do these paintings evoke a strange feeling?
ch 10 11

Leonardo da Vinci (1452-1519)
Mona Lisa (1503)
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….
ch 10 12

The Dreyfus Madonna: da Vinci 1469 ch 10 13

Why did Leonardo become so famous?
One secret: ch 10 14

The Last Supper: da Vinci, 1498 ch 10 15

The virgin of the rocks: da Vinci, 1483-
1486 ch 10 16

Madonna Litta: (da
Vinci)
1490-1491 ch 10 17

The Santa Trinita
Madonna: Cimabue
(1260/80) ch 10 18

Coronation of the virgin altarpiece from San Domenico:
Fra Angelico, 1434 ch 10 19

ch 10
The presentatio n of the virgin:
Giotto,
1305
20

Madonna in Glory:
Giotto, 1311 ch 10 21

Why did Leonardo become so famous?
• Or what made Leonardo’s pictures so special?
ch 10 22

1260/80
1311
1434
Historical depiction of
Madonna
1469 ch 10
2000
23

1260/80
1311
1434
Historical depiction of
Madonna
1469 ch 10
2000
24

ch 10 25

What I think:
• Everything before Leonardo was very flat.
• These pictures were so crisp clear.
• No ambiguity.
• Leonardo (A-rod) made things more ambiguous.
ch 10 26

Leonardo found two tricks
• To depict distance, L used (but not W, definitely not A-rod)
– Linear perspective
– Atmospheric perspective ch 10 27

Leonardo used lots of pictorial cues to depict depth ch 10 28

ch 10
Atmospheric perspective
Things get vague when they are away.
29

Things get smaller when they are away.
ch 10 30

Linear perspective ch 10
Things get smaller when they are away.
31

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 ch 10 32

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?
ch 10 33

ch 10
• 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.
34

Monocular pictorial cues
• Occlusion
• Relative height
• Relative size
• Familiar size
• Atmospheric perspective
• Linear perspective ch 10 35

Occlusion ch 10 36

Relative height ch 10 37

Relative size ch 10 38

Atmospheric perspective ch 10 39

ch 10 40

ch 10 41

ch 10 42

Texture gradient ch 10 43

ch 10 44

• 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.
ch 10 45

Visual Illusions ch 10 46

(A)
(B)
(A) ch 10
(B)
47

ch 10 48

ch 10 49

ch 10 50

ch 10 51

Tell me why these pictures bizarre?
• Any idea?
ch 10 52

What makes these pictures surreal?
ch 10 53

What makes these pictures surreal?
ch 10 54

Any idea?
ch 10 55

My guess:
• These pictures deliberately violate pictorial cues.
–  which evokes a strange feeling.
–  these pictures depict impossible scenes by reversing depth relations.
ch 10 56

• Violating some depth cues
– Deliberately introducing contradictory depth information.
ch 10 57

What makes these pictures surreal?
Violating linear perspective ch 10 58

ch 10 59

ch 10 60

ch 10 61

How to make an Escher figure.
ch 10 62

ch 10 63

Other cues
• Movement parallax
– Nearby objects move faster than distant objects
– http://video.google.com/videoplay?docid=-
5983729407150064898&q=motion+parallax&t otal=43&start=0&num=10&so=0&type=search
&plindex=2 ch 10 64

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) ch 10 65

Binocular Depth Information ch 10 66

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?
ch 10 67

Before
I guess we were all like these.
And then
Now
We got two eyes. How come?
ch 10 68

Something to do with evolution?
• Some kind of evolutionary force
• Having two eyes is evolutionarily advantageous?
• What advantage is it?
ch 10 69

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.
ch 10 70

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 ch 10 71

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.
ch 10 72

ch 10 73

Binocular disparity
& Binocular depth cues ch 10 74

Demo
Step 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.
ch 10
Got double images for the unfocused finger? But why?
75

Binocular disparity
• Your two eyes are getting different images
 disparity
 double images
Corresponding points
Corresponding points
No disparity ch 10 disparity
76

Small disparity
Large disparity ch 10
No disparity
77

Horopter (Vieth-
Muller circle) ch 10 78

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”) ch 10 79

Binocular disparity
-

OK, then open your right eye and close your left eye . What happens? Repeat this several times.
ch 10 80

Binocular disparity
-

OK, then open your right eye and close your left eye . What happens? Repeat this several times.
ch 10 81

• 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.
ch 10 82

• Your unfocused finger moves to the left.
• Why? ch 10 83

small distance large distance
Small disparity ch 10 large disparity
84

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?
ch 10 85

2 types of disparity
F uncrossed disparity
P ch 10
C
P crossed disparity
86

• 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.
ch 10 87

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.
ch 10 88

Emmert’s law
• S = R x D
– S: Perceived size
– R: retinal image
– D: perceived distance ch 10 89

ch 10 90
Fig. 10-33, p. 248