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OD2-BVOM > 5. Steropsis and Depth Perception > Flashcards

5. Steropsis and Depth Perception Flashcards

1
Q

what is depth perception based on

A

multiple cues, each of which can sitmulate depth perception by themselves

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2
Q

what is a depth cue

A

a feature of the ocular images which changes w/ object depth

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3
Q

how are depth cues categorized in

A

2 ways, based on the need for binocular vision (mono cues and binocular cues)
2. the type of depth judement the cues support (absolute vs relative)

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4
Q

what are monocular depth cues

A
  1. visual angle cues
    - known size, looming, perspective, texture gradients
  2. contrast cues
    - contrast, aerial perspective, overlay, shadows and shading
  3. motion cues
    - motion parallax, knetic depth effect
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5
Q

what does absolute depth tell the observer
how are they judged
what are they analogous to

A

tells the oberver how far objects are from themselves or form other objects

  • judged in absolute units of distance
  • analogous to egocentric direction
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6
Q

what are the absolute depth cues

A
  1. known size
  2. stereopsis based on both horizontal and vertical disparity
  3. convergence registration
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7
Q

what information is required for visually guided motion

A

absolute depth info

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8
Q

what does relative depth tell the observer
what are they judged as
what are they analogous to

A

tells the observer about relative order and proportion in depth

  • judged as % diff or as depth ratios
  • analogous to oculocentric direction
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9
Q

what are relative depth cues

A

stereopsis when based only on horiz disparity

-all cues that aren’t aboslute cues

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10
Q

how are all these depth cues put together for a single depth perception

A
  1. each relative depth cue is first promoted to absolute depth
    (oculocentric to egocentric)
  2. absolute depth cues are averaged by weight (strength in environment)
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11
Q

why do we have so many depth cues

A

reliability

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12
Q

why does stero not equal awareness of convergence

A

convergence creates a separate depth cue called “convergence registration” or “convergence corollary discharge”
-stero creates depth even when the eyes are fixed

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13
Q

what is the main stimulus to stereo

A

horizontal relative disparity

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14
Q

a single absolute disparity doesn’t stimulate stereopsis..what does

A

2

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15
Q

the approx formula for real depth shows that stero depth stimulus is proportional to…

A
  1. the physical depth interval btwn compared objects
  2. interpupillary dist
    - larger pd=stero depth more easily
  3. inverse square of viewing distance
    - 1/2 viewing dist, stero stimulus quadruples
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16
Q

what is the projected depth

A

horiz relative disparity ay also be created by artificial lateral displacement of the ocular images in diff directions

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17
Q

what are some projected depth methods

A
  1. wheatstone and brewster steroscopes
  2. vectograms and red/green anaglyphs
  3. rapid alternating img projection
  4. free fusion and autostereograms
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18
Q

what depth methods do 3D movies

A

projected depth methods

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19
Q

stereoscopes are a type of _____ that present stereo images

A

haploscope

-devices that allow independent stimulation of each eye

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20
Q

what are vectograms and R/G anaglyphs

A

stereoscopes w/o lenses or mirrors

21
Q

what are advantages to vectograms and R/G anaglyphs?

disadvantages?

A

advantage: more natural viewing (no optics), physically compact

disadvantage: polarized vectograms must be replaced periodically bc the polaroid material decays
- red/gree anagylphs may induce rivalry and suppression

22
Q

what are the advantages/disadvantages of free fusion

A

advantage: enables fusion of stero cards w/o stereoscope
- important VT skill

dis: diplopic images
- requires much more dissocation of acc from vergence, compared to stereoscopes

23
Q

what is the principle of autostereograms

A

each eye’s image is projected to it in a limited optical cone in physical space
-each cone contains a full image for one eye

24
Q

what are the types of autosterograms

A

lenticular displays

parallax barrier displays

25
Q

what are the advantages/dis of autostereograms

A

ad: allows stereoscope viewing w/o special glasses or stereoscope optics
disad: limited head position range in physical space

26
Q

why is horizontal relative disparity only a relative depth cue

A

bc relative disparity alone is ambiguous about absolute depth

27
Q

how does vision ocnvert horiz relative disparity into absolute depth

A

by promoting horiz relative disparity by way of known size, vertical disparity, and convergence registration

28
Q

what is vertical disparity

A

stimulation of noncorresponding points in the vertical dimension of the retinas

29
Q

what causes vertical disparity in normal viewing

A

vertical disparity is stimulated by near objects to the side of the head

  • these objects are seen as taller by thte ey eon the same side as the objects
  • the size difference causes vertical disparity
30
Q

why is veritcal disparity visually useful to vision

A

it is monotonically related to absolute depth

31
Q

what are the limitations of the verticla disparity cue

A
  1. needs large stimuli and large visual field

2. slow perceptual process: better in static vision

32
Q

what is convergence registration

A

the ability to sense convergence angle, and use that info for depth perception

33
Q

what are convergence registrations 2 roles in vision

A
  1. absolute depth cue (1:1 relationshipof abs depth to convergence)
  2. promotes relative disparities into absolute depth
34
Q

when does convergence registration work best

A

in near vision, like stereopsis

35
Q

what is convergence micropsia

A

convergence causes the perceived retinal image to shrink, divergence causes it to grow

36
Q

what is convergence micropsia neurally linked to

A

convergence innervation

37
Q

when is convergence micropsia very visible during

A

prism vergences

38
Q

what is convergence micropsis’s possible role in normal vision

A

a contributor to size constancy

39
Q

what is SILO

A

small-in/large-out

  • small and large refer to perceived size
  • in and out refer to perceived distance
40
Q

how does SILO work

A

convergence micropsia caues the perceived size change

convergence registration causes the perceived distance change

41
Q

what can SOLI occur

A

uncommon exception to SILO
possible cause w/ BO prism
-pt doesn’t sense convergence registration, no depth stimulation comes from convergence
-convergence micropsia still functions so images shrink
-shrinking image stimulates the visual angle depth cue
-smaller image causes a report of greater distance

42
Q

what are preattentive image features

A

those that reveal a pattern even when you are not attending them

  • color and motion
  • stereopsis
  • seem to pop out
43
Q

attentive image features require what to recognize a pattern based o nthem

A

attentive fixation

-these include patterns defined by contour orientation, angles, curvature, etc

44
Q

what is the significance of preattention in stereo

A

patients who have good stereo do not study a stereogram to see the depth bc depth will pop out to the patient

45
Q

why does threshold stereo require more foveal viewing time

A

bc the disparities are tiny, cuases judment delays

46
Q

what is patent stereopsis

what is it associated w/

A

compelling sense of depth

  • proportional to disparity
  • assoicated w/ single vision and smaller disparities
47
Q

what is qualitative stereopsis

what is it associated w/

A

uncertain depth

  • objects are much nearer or farther than fixation
  • amount of depth unclear
  • associated w/ diplopic images and larger disparities
48
Q

what are the 2 parallel neural pathways from retina to visual cortex

A

parvo and magno

OD2-BVOM (6 decks)

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