SpaceDepth Perception - PowerPoint PPT Presentation

Title: SpaceDepth Perception


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PSY 3520 Sensation and Perception
Space/Depth Perception
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Space/Depth Perception Lecture Outline

• Cue Approach
• A. Oculomotor Cues
• B. Pictoral Cues
• C. Motion-produced Cues
• D. Binocluar Disparity
• stereoscope
• 1. Corresponding Retinal Points
• 2. Disparity Information and the Brain
• Perception of Size
• A. Visual Angle, Retinal Size, and Distance
• B. Perceiving Size as Visual Angle Changes
• Law of Size Constancy
• C. Size Constancy and Depth Perception
• Law of Visual Angle
• Emmerts Law
• D. Illusions of Size

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I. Cue Approach

• The cue approach postulates connections between
  stimuli in the environment, the images these
  stimuli present to the retina, and perceived
  depth
• We will discuss four groups of depth cues
• Oculomotor Cues
• Pictoral Cues
• Motion-produced Cues
• Binocular Disparity

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Oculomotor Cues

• These are cues that depend on our ability to
  sense the position of our eyes and tension in our
  eye muscles
• Convergence/Divergence
• Convergence eyes move inward to focus close up
  objects
• Divergence eyes move away from each other to
  focus an object farther away.

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Oculomotor Cues

• Accommodation the shape of the lens changes
  shape to focus objects
• Lens bulges to focus near objects
• Lens flattens to focus objects farther away

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Pictoral Cues

• Cues that can be depicted in a still picture or
  from the picture formed on the retina.
• Overlap (Interposition or Occlusion) objects
  that are closer to us block our view of objects
  that are farther away

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Relative Size

• Larger objects appear to be closer (person who is
  farther away appears smaller)

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Relative Height

• Objects closer to the horizon appear to be
  farther away

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Atmospheric/Aerial Perspective

• Distant objects appear less sharp because the
  observer must look through air and particles
  between them and the object.

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Linear Perspective

• Convergence of parallel lines.

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Texture Gradient

• Can see more detail in close objects. Lose
  detailed texture information for farther objects.

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Shading/Relative Brightness

• Surfaces facing a light source are brighter and
  surfaces facing away are darker.

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Shading/Relative Brightness
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Shading/Relative Brightness
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Motion-Produced Cues

• These are cues that rely on movement to the
  observer, or movement of objects in the
  environment
• Motion Parallax
• Deletion and Accretion
• Kinetic Depth Effect

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Motion Parallax

• The direction and speed of motion is different
  for objects due to their position relative to the
  observers fixation point.

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Deletion and Accretion

• Deletion observer moves and closer object
  covers more of an object farther away.
• Accretion observer moves and closer object
  covers less of an object farther away.

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Kinetic Depth Effect

• A 2-dimensional picture is seen in 3-D becaued of
  motion.
• kinetic depth

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Binocular Disparity

• Binocular means it depends on both eyes.
• Relates to the fact that we have two eyes that
  see the world from slightly different positions.

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Binocular Disparity

• That the position of our eyes is related to depth
  perception has been illustrated by the use of a
  stereoscope.

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Stereoscope

• The stereoscope uses slightly offset pictures to
  produce the illusion of depth.

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Binocular Disparity

• Because the eyes present us with two different
  images of the visual scene, we must combine the
  disparate images to form a single percept of the
  scene.
• This is called fusion.
• To enable us to merge the disparate images, we
  have corresponding retinal points.

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Corresponding Retinal Points

• For every point on one retina, there is a
  corresponding point on the other retina.
• These corresponding points on each retina would
  overlap if one retina could be slid on top of the
  other.

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Retinal Disparity
Uncrossed Disparity
Horopter images fall on corresponding retinal
points and the image is fused.
Crossed Disparity
Panums Area noncorresponding retinal images
with low retinal disparity. Observer can still
fuse images.
Outside of Panums area images can not be fused.
Have diplopia double vision.
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• Handouts

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Disparity Information and the Brain

• Barlow, Blakemore, Pettigrew (1967) found cells
  in the cortex of the cat that respond best to
  stimuli that fall on points which are separated
  by a specific degree on the retina.
• Hubel Weisel (1970) found these cells in the
  visual cortex of monkeys and they identified them
  as binocular depth cells.

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Binocular Depth Cells
Retinal Disparity
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150
300
450
600
RE
LE
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III. Perception of Size

• Visual Angle, Retinal Size, and Distance
• Perceiving Size as Visual Angle Changes
• -Law of Size Constancy
• Size Constancy and Depth Perception
• -Law of Visual Angle
• -Emmerts Law
• Illusions of Size

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Visual Angle, Retinal Size, and Distance

• The distance of an object from an observer
  affects the size of the object on the retina
  (affects visual angle).
• Visual Angle a description of the amount of
  space taken up on the retina by an object.

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Perception of Size

• Perceiving Size as Visual Angle Changes
• Law of Size Constancy
• Size Constancy and Depth Perception
• Holway Boring (1941)

Test Light
Hallway
Hallway
Comparison Light
10 ft. 120 ft.
10 ft.
Note Larger diameter of test light needed to
maintain visual angle with greater distance
Observer
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Holway Boring Study

• At the beginning of each trial the test and
  comparison circles are 1o of visual angle.
• On each trial the observers task is to adjust
  the diameter of the comparison circle to match
  the actual diameter of the test circle.

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Holway Boring Study

• 4 Phases
• Phase 1 the observer has all depth cues so
  judgments were based on the physical sizes of the
  circles
• Results supported the Law of Size Constancy

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Holway Boring Study
Phase 1
Law of Size Constancy
Adjustment in Size of Comparison Circle (in)
Distance of Test Circle (ft.)
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Holway Boring Study

• Holway and Boring began removing depth cues
• Phase 2 Observers performed the task
  monocularly
• What depth cues were removed?

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Holway Boring Study
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Holway Boring Study

• Phase 3 Observers looked through a peephole
• Observers begin to see the circles as the same
  size not as much adjustment

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Holway Boring Study
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Phase 1
Law of Size Constancy
Phase 2
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Adjustment in Size of Comparison Circle (in)
Phase 3
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Law of Visual Angle
0
50
100
10
Distance of Test Circle (ft.)
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Holway Boring Study

• Phase 4 the hallway was draped with black
  drapes.
• Minimal adjustment of the comparison stimuli by
  observers.
• With the elimination of depth cues the perception
  of size follows the law of visual angle more
  closely.

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Holway Boring Study
Why are Phase 4 and the Law of Visual Angle
different?
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Phase 1
Law of Size Constancy
Phase 2
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Adjustment in Size of Comparison Circle (in)
Phase 3
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Phase 4
Law of Visual Angle
0
50
100
10
Distance of Test Circle (ft.)
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Holway Boring Study

• The results of the Holway Boring study suggest
  that depth information, as well as visual angle
  are important for size constancy
• Gregory (1966) proposed that we have a constancy
  scaling mechanism
• Size-distance scaling
• Emmerts Law

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Illusions of SizeAmes Room
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Illusions of SizeAmes Room
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Illusions of SizeMüller-Lyer Illusion
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Illusions of SizePonzo Illusion
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Illusions of SizeMonsters