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DEPTH . PERCEPTION. Depth perception. Translation of 2 dimensional (retinal) image into a 3 dimensional image Retina only codes in 2 dimensions But we live in 3-d world Most perception requires assessing depth Particularly hand eye coordination!. Two kinds of cues for depth.

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depth

DEPTH

PERCEPTION

depth perception
Depth perception
  • Translation of 2 dimensional (retinal) image into a 3 dimensional image
    • Retina only codes in 2 dimensions
    • But we live in 3-d world
    • Most perception requires assessing depth
    • Particularly hand eye coordination!
two kinds of cues for depth
Two kinds of cues for depth
  • Monocular cues
    • One eyed!
    • Several different categories
  • Binocular cues
    • Requires coordination of both eyes
    • Depends on retinal disparity: each eye sees a slightly different image
    • Use this feedback to determine depth
monocular cues
Monocular cues
  • Three kinds
    • Accommodation
    • Kinetic or movement cues
    • Accommodation
  • Accommodation:
    • When you shift your focus from near to far or far to near, requires movement of eye muscles
    • Especially ciliary muscles
    • Feedback from these muscles provide a cue for depth
pictorial cues
Pictorial Cues
  • Picture cues
  • Available via stationary inspection (holding still!)
  • Often used by artists, architects, animation, etc.
  • Obey Gestalt Rules
  • Use 2-D image to imply a 3-D image
pictorial cues1
Pictorial Cues
  • Size:
    • As objects move farther away the size of the retinal image gets smaller in direct proportion to the distance
    • This becomes a cue for depth
    • Note: assumes Object constancy
      • objects don’t change size
      • Compare ‘familiar’ size to retinal size
pictorial cues2
Pictorial Cues
  • Interposition:
    • If 2 opaque objects are in same line of sight, the one in front will occlude the one behind
    • The front object blocks the back object
    • Interesting cultural differences:
      • Individuals with no formal education can see in real life but NOT see it in book or picture form
      • Why?
pictorial cues3
Pictorial Cues
  • Light and Shadow
    • Objects that have depth cast shadow
    • Use shadow to judge depth and distance
    • Movement of shadow can even tell movement
pictorial cues4
Pictorial Cues
  • Perspective
    • Lines or texture converge with distance
    • Linear perspective
    • Texture perspective
    • Also aerial perspective: higher objects appear fuzzy
  • Interesting applications:
    • Learning to fly and aerial perspective
    • Visual Cliff research
      • Animals who are precocial show fear from birth
      • Animals who are not precocial show fear once they begin moving on their own
      • Why?
kinetic or motion cues
Kinetic or motion cues
  • Motion parallax
    • Assume observer is moving, not the world
      • Get this when sitting at stop light and other car moves slightly
      • Feel like are moving backward
    • Relative movement of objects differ with distance:
      • Close objects move fast
      • Far objects move slowly
  • Kinetic depth effect
    • Depends on moving objects
    • objects change shape with movement and distance
binocular cues
Binocular Cues
  • Convergence
    • eyes move inward for near objects
    • Eyes move outward for far objects
    • This feedback does two things:
      • Changes degree of disparity
      • Movement of eye muscles is cue for depth
binocular cues1
Binocular Cues
  • Binocular disparity
    • Each eye sees slightly different visual field
    • The degree of overlap gives clue to distance
      • Little overlap: object is far away
      • Lots of overlap: object is near
      • Can actually calculate depth/distance this way:
        • triangulate the distance
        • This is how surveyors work
  • You have a dominant and non-dominant eye:
    • How to tell?
    • Hold figure about 12” from nose, line it up with distant vertical object
    • Close left eye, leaving right open; note how far finger “jumps”
    • Close right eye, leaving left open: note how far finger “jumps”
    • The eye for which the finger “jumps” the least is your dominant eye
  • Why? This is the eye the brain uses most, the other eye becomes the comparator
      • When there is too much disparity, the brain only attends to dominant eye
      • Ignores other eye
      • If this continues for too long- the pathway to the non-dominant eye dies
why is it important to use our senses
Why is it important to “use” our senses?
  • Binocular disparity drives this home
    • The brain receives confusing signals, it will stop attending to the “bad” signal
  • If a sense is not used, the brain will begin to ignore it:
    • Brain tissue will die off or be used for other senses
    • Thus, it is not that people who are blind hear better, but their brain stops using optical information and only attends to hearing
    • Is really that they pay better attention to hearing
  • A variety of research has shown: Use it or lose it!