How Far Away Is It? Depth Perception

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How Far Away Is It?Depth Perception
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Depth Perception

• The ability to see objects in three dimensions
  although the images that strike the retina are
  two-dimensional, allows us to judge distance
• How do we see a 3-D world using only the 2-D
  retinal images?
• We are able to see in 3-D because the visual
  system can utilize depth cues that appear in the
  retinal images

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Gibson Walks Visual Cliff

• A laboratory device for testing depth perception
  in infants and young animals
• Infants that have been crawling for about a month
  are reluctant to crawl past the edge of the
  visual cliff
• Other animals had similar results.
• Suggests that depth perception, to some extent,
  is inborn but needs experience of crawling

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Visual Cliff
The Visual Cliff Experiment
Click on link above to view the visual cliff
experiment
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Depth Perception Monocular Depth Cues
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Monocular Cues

• Depth cues that require the use of only one eye
• Monocular depth cues include
• relative size
• relative motion
• interposition
• relative height
• texture gradient
• relative clarity
• linear perspective.

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Monocular Depth Cues Relative Size

• Using the perceived size of a familiar object to
  determine depth
• The larger the object appears, the closer the
  object is to the viewer
• The smaller the object appears, the farther away
  it is to the viewer.

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Monocular Depth Cues Relative Motion (Motional
Parallax)

• A person who is moving can determine depth by
  focusing on a distant object.
• As we move, objects that are actually stable may
  appear to move
• Objects further away than the object of focus
  will appear to move slowly in the same direction
  as the subject is moving.
• Objects closer than the object of focus will
  appear to move quickly in the opposite direction.

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Relative Motion
In this example, the passenger is moving past a
stable world. If she fixes her gaze on the
bridge, objects behind it will appear to move
forward. The farther away the object is, the more
slowly it will appear to move. Objects in front
of the fixation point appear to move backward.
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Monocular Depth Cues Interposition/Overlap

• Method of determining depth by noting that closer
  objects partially obstruct/block the more distant
  objects
• Also called overlap

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Monocular Depth Cues Relative Height

• Method of determining depth by noting that
  distant objects appear higher in your field of
  vision than do closer objects
• This reversed above the horizon where higher
  objects seem closer.

You know that the trees and houses are farther
away than the lake because they are higher up in
the drawing than the lake is.
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Monocular Depth Cues Texture Gradient

• Method of determining depth by noting that
  distant objects have a blended or smoother
  texture than nearby objects

Individual flowers are visible in the foreground,
but in the distance they look like a smooth
carpet.
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Monocular Depth Cues Relative Clarity (Aerial
Perspective)

• Method of determining depth by noting that
  distant objects are less clear than nearby
  objects
• Tends to work outdoors because light from distant
  objects passes through more atmosphere, we
  perceive hazy objects as farther away than sharp,
  clear objects

The distant mountains look blue hazy because of
dust moisture in the atmosphere.
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Clarity as a Cue to Distance
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Monocular Depth CuesLinear Perspective

• Method of determining depth by noting that
  parallel lines appear to converge in the distance
• The lines appears to eventually merge on the
  horizon.

The sides of the road or track seem to converge
in the distance.
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Monocular Depth CuesLight and Shadow

• Nearby objects reflect more light into our eyes.
  
• Given two identical objects, the dimmer one seems
  farther away.
• Brain assumes that light comes from above.

Watch as the picture flips upside down.
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Depth Illusions

• Sometimes our perception of depth can be tricked.
• Click on the video link below to view the
  illusion.

Rotating Face Mask Illusion
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Can you apply these principles to a painting?

• On Your White Board write the following
• Relative Size
• Interposition
• Relative Height
• Texture Gradient
• Relative Clarity/Aerial Perspective
• Linear Perspective
• Light Shadow

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Explain how those terms are being used in this
picture.
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Accomodation

• Accommodation is also used by the brain to
  estimate distance.
• Brain takes into account how the muscles in your
  eye affect your lens - thickens (for nearby
  objects) or flattens (for far away objects).
• However, we rely on pictorial cues more than
  this.

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Depth Perception Binocular Depth Cues
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Binocular Cues

• Depth cues that require the use of both eyes
• There are two types Retinal Disparity
  Convergence

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Retinal/Binocular Disparity

• A binocular depth cue resulting from slightly
  different images produced by the separation of
  the retinas in the left and right eye
• Because our eyes are about 2 ½ inches apart, the
  retina receives slightly different images of the
  world.
• The greater the difference between the two
  images, the closer the object is to the viewer.
• The more alike the two images, the further away
  the object is perceived.
• Is most effective when the item is quite close to
  the person
• Example hold a pencil just in front of your
  nose and close one eye, then the other. The
  pencil should move showing the disparity. Now
  focus on something far away and do the same. It
  should not move very much showing less disparity.
  

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Some Peoples Eyes are Further Apart than 2 ½
inches
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Binocular Depth Cues Finger Sausage
Hold your two index fingers about 5 inches in
front of your eyes, with their tips half an inch
apart. Now look beyond them and note the weird
result. Move your fingers out farther and the
retinal disparityand the finger sausagewill
shrink.
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Stereogram

• Another way to create the illusion of depth
  through binocular stereopsis is with an
  Autostereogram
• An autostereogram is formed by superimposing two
  repeating patterns
• The two patterns are slightly offset, and when
  viewed properly, this offset is seen as a
  binocular disparity

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Stereogram
To see the 3-D image, first view the picture
closely. Focus your eyes as if you are looking
at some far off distant object (look through the
picture). Try relaxing your eyes so they swing
outward. Without changing your focus, slowly
move away from the picture. The image will begin
to to come into focus. Do you see a Face? If you
have trouble, it just means your eyes are
difficult to trick, they want to focus at the
proper depth!
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Convergence

• A binocular depth cue related to the tension in
  the eye muscles when the eyes track inward to
  focus on objects close to the viewer
• The brain notes the angle of the convergence and
  then computes the distance of what you are
  focusing at.
• The more tension in the eye muscle, the closer
  the object is
• Works best at close distances

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Julian Beevers Sidewalk Chalk Art
Want to see more? Goto http//www.etntalk.com/sid
ewalk/
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Julian Beevers Sidewalk Chalk Art
Watch How He Does It
Watch a video montage of his work
Want to see more? Goto http//users.skynet.be/J.B
eever/pave.htm