Chapter 10:
Perceiving Depth
and Size
Perception – Spring 2013
© Takashi Yamauchi
Alex Proaps
DO NOT share these outside of class under any circumstances
Overview of Questions
• How can we see far into the distance based on
the flat image of the retina?
• Why do we see depth better with two eyes than
with one eye?
• Why don’t people appear to shrink in size when
they walk away?
• What are some problems with 3D movies?
2D to 3D?
• The brain constructs depth information from 2D
images, using “cues”
Cue Approach to Depth Perception
• Oculomotor cues - sensing eye position and
muscle tension
– Convergence (and divergence)
Cue Approach to Depth Perception
• Oculomotor cues - sensing eye position and
muscle tension
– Accommodation
Cue Approach to Depth Perception
• Monocular cues come from one eye
– Pictorial cues
• sources of depth information from 2-D images
Tell me why these pictures look bizarre.
7
Up and Down:
Escher
ch 10
8
De Chirico
10
Monocular pictorial cues
1.
2.
3.
4.
5.
Occlusion (interposition)
Relative height (height in plane)
Relative size
Familiar size
Atmospheric perspective
6. Texture gradient
7. Shadows (shading and contours)
8. Linear perspective (perspective convergence)
9. Figure/Ground
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Occlusion
Relative height
• Objects below the horizon that are higher in the
field of vision are more distant
Relative size
• Objects are equal size
– closer one will take up more of your visual field
Familiar size
Texture gradient
• equally spaced elements are more closely packed as
distance/depth increases
Atmospheric perspective
• distance objects are
– fuzzy,
– vague,
– may have a blue tint
Shadow
• indicate where objects are located
– enhance 3-D of objects
• light from above heuristic
Linear perspective
• parallel lines appear to come together in the distance
Figure-ground segregation
Motion-Produced Cues
• Motion parallax
– close objects in direction of movement move rapidly
– objects in the distance appear to move slowly
Motion-Produced Cues
• Deletion and accretion - objects are covered or
uncovered as we move relative to them
Binocular Depth Information
• But we have two eyes, not one.
Demo
1. Hold one finger about 8 inches in front of
you and the other about 15 inches in
front of you.
2. Focus on the one that is further from you,
and move the other finger back and forth.
Get double images
for the unfocused
finger? But why?
26
Binocular Depth Information
• Binocular disparity - difference in images from two eyes
– examine corresponding points on the two retinas
Binocular Depth Information
• Horopter - imaginary sphere that passes through
the point of focus
Binocular disparity
• Objects on horopter
– Corresponding points
Corresponding
points
No disparity
Disparity
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Binocular disparity
• Objects not on horopter
– Non-corresponding points
– B and G instead of D
Corresponding
points
No disparity
Disparity
30
Demo
 OK, then open your right eye and
close your left eye. What happens?
Repeat this several times.
31
Demo
 OK, then open your right eye and
close your left eye. What happens?
Repeat this several times.
32
Demo
 This time change the distance between your focused
and unfocused fingers.
• That finger moves further left.
33
• Your unfocused finger moves to the left.
34
small
large
distance
distance
Small disparity
Large disparity
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Physiology of Depth Perception
• V1 – where signals are “pooled”
• Specific neurons in V1, V2, V3 respond to specific
degree of disparity between images on right and left
retinas
Physiology of Depth Perception
• V1 – where signals are “pooled”
• Specific neurons in V1, V2, V3 respond to specific
degree of disparity between images on right and left
retinas
– binocular depth cells
– disparity selective cells
Stereopsis
• Depth information provided by binocular disparity
– Stereoscopes
– 3-D movies
Stereopsis
1. Two synchronized pictures
2. Project both images simultaneously
3. Observers must see the two images with the two
eyes separately
3-D movies
• The Hobbit grossed $84.7 million in its first
weekend
– highest December opening in history
– out grossed Avatar and I Am Legend
– Paul Young (screenrant.com) film makers use 3D
to make money, not to enhance the viewing
experience.
Why do we hate post- conversion 3-D?
• Write down a few of your ideas
Pioneering use of depth cues in film
• Coraline
– Laika used depth cues to convey different moods
– Paranorman (2012) is more recent example
Pioneering use of depth cues in film
Perception of distance
• Absolute distance
– Where am I?
• Relative distance
– Where are things around me?
Perception of distance
• Absolute distance
– Where am I?
• Relative distance
– Where are things around me?
– We use depth and size cues to help us perceive
distance
Experiment by Holway and Boring
• Judgments of size vary based on depth cues
Experiment by Holway and Boring
• Judgments of size
• When we have depth cues
Experiment by Holway and Boring
• Judgments of size
• When we have depth cues
– based on physical size
Experiment by Holway and Boring
• Judgments of size
• When we have depth cues
– based on physical size
• When we have no depth information
Experiment by Holway and Boring
• Judgments of size
• When we have depth cues
– based on physical size
• When we have no depth information
– based on size of the retinal images
Size-Distance Scaling
• Visual angle - angle of object relative to the observer’s eye
– depends on both the size of the object and the
distance from the observer.
Size-Distance Scaling
• Image size is inversely proportional to distance
Size-constancy scaling
• Perception of an object’s size remains relatively
constant even if the size of the retinal image
changes.
• Emmert’s Law
– Perception of size depends on retinal size and
perceived distance
Size-Distance Invariance
• Emmert’s Law
– size depends on retinal size and perceived distance
•S = R x D
– S = perceived size
– R = retinal size
– D = perceived distance
Size-Distance Invariance
• Emmert’s Law
– size depends on retinal size and perceived distance
•S = R x D
– S = perceived size
– R = retinal size
– D = perceived distance
• 5 ft = (.2 x 25 ft)
• 5 ft = ( .05 x 100 ft)
Sun and the moon have the same visual angle during
eclipse.
Visual Illusions
• Nonveridical perception occurs during visual illusions.
1. Forced perspective
2. Müller-Lyer illusion
3. Ponzo illusion
4. Moon illusion
5. Hollow face
6. Forced perspective
Forced perspective
Müller-Lyer illusion
Why does this Müller-Lyer Illusion occur?
• Misapplied size-constancy scaling:
– size should remain constant if the size of the
retinal image changes?
– Corners of arrows confuse the retinas
Problems with this explanation
with no corners
Problems with this explanation
3-D displays
Why does this Müller-Lyer Illusion occur?
• Conflicting cues theory
– actual length of the vertical lines
– overall length of the figure
– integrated into a compromise perception of length
Ponzo Illusion
Ponzo Illusion
• One possible explanation is misapplied size-constancy
scaling.
Ponzo Illusion
• One possible explanation is misapplied size-constancy
scaling.
The Ames Room
The Ames Room
• Two people of equal size appear very different in
size in this room.
The Ames Room - continued
• Size-distance scaling
• Relative size
Moon Illusion
• The moon appears larger on the horizon than when
it is higher in the sky.
Moon Illusion - theories
• Apparent-distance theory
– horizon moon is surrounded by depth cues
– moon higher in the sky has none
Moon Illusion - theories
• Apparent-distance theory
– “flattened heavens”
Moon Illusion – theories continued
• Angular size-contrast theory - the moon appears
smaller when surrounded by larger objects
– large expanse of the sky makes it appear smaller
Moon Illusion – theories continued
• Actual explanation may be a combination of a cues.
– Other factors :
• Eye elevation
• Atmospheric perspective
• Perceived change in color
• Occulomotor cues
Hollow face
• Shadows are important depth cues
Why do we hate post- conversion 3-D?
• Editing of 3D films cannot be as rapid as 2D films
– Takes longer for the brain/eye to "get" the scene
– Slower apparent motion
– Motion sickness
• Also happens when you speed up rate (The Hobbit)
Why do we hate post- conversion 3-D?
• Focus at one distance and converge at another
– Forced perspective
– Headaches
– Eyestrain