Depth Perception, part II Lecture 12 (Chapter 6) Jonathan Pillow - - PowerPoint PPT Presentation

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Depth Perception, part II Lecture 12 (Chapter 6) Jonathan Pillow - - PowerPoint PPT Presentation

Feb 19, 2024 289 likes •792 views

Depth Perception, part II Lecture 12 (Chapter 6) Jonathan Pillow Sensation & Perception (PSY 345 / NEU 325) Spring 2019 1 nice illusions video - car ad (2013) (anamorphosis, linear perspective, accidental viewpoints, shadows,

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Depth Perception, part II

Lecture 12 (Chapter 6)

Jonathan Pillow Sensation & Perception (PSY 345 / NEU 325) 
 Spring 2019

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nice illusions video - car ad (2013)

(anamorphosis, linear perspective, accidental viewpoints, shadows, depth/size illusions) https://www.youtube.com/watch?v=dNC0X76-QRI

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Accommodation - “depth from focus”

near far

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Depth and scale estimation from accommodation

“tilt shift photography”

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Depth and scale estimation from accommodation

“tilt shift photography”

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Depth and scale estimation from accommodation

“tilt shift photography”

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Depth and scale estimation from accommodation

“tilt shift photography”

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Depth and scale estimation from accommodation

“tilt shift photography”

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more on tilt shift: Van Gogh


http://www.mymodernmet.com/profiles/blogs/van-goghs-paintings-get

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Tilt shift on Van Gogh paintings

http://www.mymodernmet.com/profiles/blogs/van-goghs-paintings-get

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countering the depth-from-focus cue

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Pictorial Non-Pictorial

  • occlusion
  • relative size
  • shadow
  • texture gradient
  • height in plane
  • linear perspective
  • motion parallax

Monocular depth cues:

  • accommodation

(“depth from focus”)

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  • Binocular depth cue: A depth cue that

relies on information from both eyes

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Two Retinas Capture Different images

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Finger-Sausage Illusion:

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Pen Test:

Hold a pen out at half arm’s length With the other hand, see how rapidly you can place the cap on the pen. First using two eyes, then with one eye closed

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Binocular depth cues:

  • 1. Vergence angle - angle between the eyes

If you know the angles, you can deduce the distance convergence divergence

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  • 2. Binocular Disparity - difference between two retinal images

Stereopsis - depth perception that results from binocular disparity information (This is what they’re offering in 3D movies…)

Binocular depth cues:

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Retinal images in left & right eyes

Figuring out the depth from these two images is a challenging computational problem. (Can you reason it out?)

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Disparity: difference between points in L and R eye images

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Horopter: circle of points that fall at zero disparity (i.e., they land on corresponding parts of the two retinas) A bit of geometric reasoning will convince you that this surface is a circle containing the fixation point and the two eyes

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point with crossed disparity appears closer point with uncrossed disparity appears further

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Is this a simple picture or a complicated computational problem?

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Interpreting the visual information from three circles

Known as the “correspondence problem” - which points in the left eye go with which points in the right eye?

This one requires an accidental viewpoint

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Wheatstone’s stereoscope

  • device for presenting one different images to the two eyes

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Free fusing - focusing the eyes either nearer or farther than this image so that each eye sees a different image

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Free fusing - focusing the eyes either nearer or farther than this image so that each eye sees a different image “Crossed-fusion”

L retina R retina

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Free fusing - focusing the eyes either nearer or farther than this image so that each eye sees a different image “uncrossed fusion”

L retina R retina

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Random Dot Stereogram - same concept, but no detectable “features” in either image. Details of dot pattern allow brain to solve the correspondence problem

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“Magic Eye” images use same principle

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If you were designing a visual system, how might you go about designing neurons tuned for different disparity?

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The brain solves this problem with disparity-tuned neurons

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Binocular Vision and Stereopsis How is stereopsis implemented in the human brain?

  • Input from two eyes must converge onto the same cell
  • Many neurons: respond best when the same image falls on

corresponding points in the two retinas
 (this is the neural basis for the horopter)

  • However: many neurons respond best when similar images
  • ccupy slightly different positions on the two retinas
  • i.e., these neurons are “tuned to a particular disparity”

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Panum’s fusional area: only certain range of disparities that the brain can fuse

  • comes from distribution of disparity-tuned neurons

Panum’s fusional area

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Depth Illusions

Müller-Lyer Illusion

http://www.michaelbach.de/ot/sze_muelue/index.html

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In which image are the two horizontal lines the same length?

(Ans: second from left)

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Two figures are the same size

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“Terror Subterra”

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“Terror Subterra”

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red lines are all the same length

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Depth / Size illusion

  • all 3 cars take up the same space in the image + on your retina!

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Strabismus

  • eyes are not aligned,

so different images fall

  • n the fovea
  • If not corrected at an

early age, stereopsis will not develop stereoblindness: inability to use binocular disparity as a depth cue.

Defects in Stereopsis

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Binocular Rivalry

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Two stimuli battle for dominance of the percept

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  • monocular depth cues
  • binocular depth cues (vergence, disparity)
  • horopter
  • crossed / uncrossed disparities
  • free fusing
  • random dot stereogram
  • stereoscope
  • “correspondence problem”
  • panum’s fusional area
  • strabismus / stereoblindness
  • binocular rivalry (in book)

Chapter 6 Summary:

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