Sensation & Perception
Ch. 8: 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
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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De 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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1260/80
1311
1434
2000
Historical depiction of
Madonna
1469
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1260/80
1311
1434
2000
Historical depiction of
Madonna
1469
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What I think:
•
•
•
•
Everything before Leonardo was very flat.
These pictures were so crisp clear.
No ambiguity.
Leonardo made things more ambiguous.
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Leonardo found two tricks
• To depict distance, L used (but not W)
– 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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How did they reproduce the world?
• Pictorial cues:
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• This simple trick was very difficult to find
before Renaissance.
• Because religion was at the center of
everything.
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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
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Visual Illusions
• http://users.skynet.be/J.Beever/pave.htm
• http://www.magiceye.com/
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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
Now
I guess we
were all like
these.
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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Why are two eyes better than one
eye?
• Depth perception:
• Depth perception is important, because the
physical space we live in is three
dimensional.
• Capturing the three dimensionality of the
world is significant for survival, I guess.
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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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How do we obtain depth
information using two eyes?
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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 depth cues
• Binocular disparity
• Quick demonstration
– Close your right eye. Hold your one finger
about 6 inches in front of you and position it so
it is partially covering an object in the distance.
Look directly at the distant object, then switch
eyes. When you switch eyes, how does the
position of your finger change relative to the far
object?
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Figure 8.11 Location of
images on the retina for
the “Two Eyes: Two
Viewpoints”
demonstration. (a) Both
images are on the fovea
when the left eye is
open. (b) The images
are on different places
on the retina when the
right eye is open.
Fig. 8.12 Corresponding
points on the two retinas. To
determine corresponding
points, imagine that one eye is
slid on top of the other one.
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Horopler is an imaginary circle. Images on
this circle fall on corresponding points on
the two retinas.
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Fig. 8.12 Corresponding
points on the two retinas. To
determine corresponding
points, imagine that one eye is
slid on top of the other one.
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Figure 8.14 The location of the images
of Carol and Lee in the lifeguard’s
eyes. Because Carol and Lee are not
located on the horopter, their images
fall on noncorresponding points.
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Figure 8.15 Crossed disparity
occurs for objects in front of
the horopter; uncrossed
disparity occurs for objects
behind the horopter. The
arrows indicate that the retinal
images move inward, toward
the nose, as the object moves
further away.
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These disparities create
depth perception.
The angle between C and
X are called the angle of
disparity. Some neurons
respond to specific angles
of disparity.
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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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Key terms
• Monocular depth cues
• Occlusion, relative height, linear &
atmospheric perspective, texture gradient
• Movement parallax
• Binocular depth information
• Horopter, corresponding points, noncorresponding points
• Angle of disparity
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