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Binocular Vision > Stereopsis > Flashcards

Stereopsis Flashcards

1
Q

Define Depth Perception

A
  • The ability to see the world in 3D
    • Mix of binocular or monocular cues
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2
Q

Name the monocular & binocular cues?

A
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3
Q

The cues that permit interpretation of depth with one eye alone are called..?

A

Monocular or empirical cues of depth

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4
Q

Which one is hard wired vs learned (Monocular and Binocular)

A

Binocular depth cues = Hardwired

Monocular depth cues = Learned

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5
Q

List the pictorial cues (cues seen in photographs) vs. Nonpictorial cues (Monocular cues)

A

Pictorial cues

  • Retinal image size
  • Emmert’s Law
  • Size constancy (Familiar)
  • Linear perspective
  • Texture gradient
  • Imposition (interposition)
  • Aerial perspective
  • Shading (Light & shadow)

Presented in 2D representation like a photograph or painting/ Seen monocularly

Nonpictorial cues

  • Accommodation
  • Motion parallax
  • Angular declination
  • Kinetic depth effect
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6
Q

Relative (Retinal Image) Size

(Image: Which one is closer?)

A
  • No reference = assume balloons are the same size
  • When visual depth cues are removed
    • smaller retinal image = perceived farther away
    • larger retinal image = perceived as near
  • Relative size is an important depth cue when viewing a scene that includes objects whose sizes can be compared to eachother
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7
Q

Size & Perceived Distance (Emmert’s law)

A
  • Emmert’s law: The perceived size of the object producing a retinal image of a given fixed size is proportional to its perceive distance
    • Greater distance = afterimage appears to increase in size
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8
Q

Describe the moon illusion (Ex. Emmert’s Law)

A
  • Moon on horizon = Larger (interpreted as more distance)
  • Moon on Zenith = Smaller (Closer distance)
  • Even though angular subtense is the same under both conditions
  • Tree, houses, fields & other interposing objects causes the moon to appear farther away when viewed on the horizon and hence make it look larger
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9
Q

Describe Size Constancy (Familiar Size) when distance cues are not available

A
  • 2 objects with unequal retinal images
  • Same size at different distances
  • Size constancy = perceptual scaling of the perceived size of an object according to the estimate distance
  • When distance cues are not available, the visual system defaults to using reintal image size as the main cue to stimulus size
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10
Q

Describe size constancy when numerous cues are available (Natural Scenes)

A
  • Cues occurs with objects of known size
    • Ex. Taxi’s are larger than people
    • So the visual system assumes that the taxi is far away because we rely on experience
    • Even if other cues are removed, we can use familiar size to judge distance
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11
Q

Define size constancy

A
  • When people’s perception of a particular object’s sizes does not change regardless of changes in distance from the object, (even though distance affects the size of the object as it is projected onto the retina)
  • Tendency to perceive an object as being of one size no matter how far away the object is
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12
Q

What occurs when size constancy fails?

A

Size illusion occurs

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13
Q

Linear Perspective

A
  • Related to relative size, can be experienced by looking down a a long corridor or railroad track
  • The retinal image size of the rail separation is smaller int he background than the foreground creating illusion of depth
    • although they are physically the same distance from the eyes
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14
Q

Describe Texture Gradient

A
  • Bricks in the background = more densely packed
  • Densely packed object = smaller retinal image size = more distance
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15
Q

Interposition (Imposition)

A
  • Occurs when view is partially obstructed
  • Church is interposed between the viewer and mountains (perceived as lying distant to it)
  • Nearer object occldues the distant object creating a sense of depth
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16
Q

Describe Aerial Perspective

A
  • form of interposition/clarity
  • Fog, rain, smoke and smog may act as interposing elements-causing them to appear more distant and contributes to sense of depth
  • Distance objects appear less sharper than near
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17
Q

Lighting & Shading

A
  • Direction of lighting & shading of an object can tell us about the object’s depth
  • When lighting falls on an object = casts a shadow
  • Shadow falls behind the object creating a sense of depth
18
Q

Describe Accommodation

A
  • Increase accommodation to keep the object at near in focus can provide cue for depth
  • Hypothesis: level of innervation of accommodation could provide distance information
  • not used as much to judge distances
  • Accommodation = weak cue for depth perception
19
Q

Describe Motion Parallax

A
  • kinetic monocular depth cue
  • Results when a moving observer fixates on an object while noticing the relative motion of surrounding objects
  • Relative motion provides information regarding distance
  • Distance = With motion
  • Near = Against motion
20
Q
A
21
Q

Kinetic Depth Effect

A
  • Shape from motion
  • Rotating wire 2D - differential motion = give rise to 3D percept
  • Looming - rapid expansion (or shrinking) in the size of any given image
22
Q

Angular Declindation below the horizon

A
  • Monocular observer stands upright in an empty room viewing an object at 10 feet
  • Despite the absence of pictorial depth cues the observer is able to correctly judge the object’s distances
  • The object makes an angle with the horizon referred to as angular declination below the horizon
    • The visual system uses this angle to determine object distance
23
Q

BV Disadvantages

A
  • They require more neurons and neural activity
  • Two eyes MUST work together with little error
  • More prcise controlled system required

Coordination Entails

  • Eye movement coordination
  • Equal VA in both eyes
  • Binocular fusion
  • Binocularity without suppression
  • Healthy eyes without anisometropia, aniseikonia
24
Q

Misalignment between the two eyes incorrectly can produce

A
  • Strabismus (eye turn)
  • Amblyopia (reduced spatial vision in one eye)
  • Suppression or
  • diplopia
25
Q

Binocular vision (Advantage)

A
  • Spare eye
  • Wider field of eye (Major benefit)
  • Binocular summaiton
  • Stereopsis (Major benefit) - important basisi for
    • figure-ground segregation
    • Avoidance of collision with objects
    • Navigation through environment
    • Stereopsis also improves performance on near visual tasks
  • We are more accurate in perceiving depth (stereopsis) = Major advantage!!
  • Figure-ground segregation - spot camouflaged objects in some surroundings
  • Better navigation through our environment, and prevention of collisions
26
Q

Describe ground visual segregation

A
  • Depth perception would allow these columns to stand out against the natural void of the dark bg
  • Pt w/ alzheimer’s disease have issues w/ figure-ground discrimination
27
Q

List the binocular cues of depth

A
  • Stereopsis (Retinal disparity)
  • Convergence
28
Q

Describe stereopsis (Retinal Disparity

A
  • Combining info of both eyes to perceive a 3D percept
  • most accurate when images are on non-corresponding points that are close together (ex. within panum’s fusional area)
  • When fixating at distance object, the monocular images of the near object will NOT fall on corresponding points, but will have disparity
    • near object = 3D
  • Strongest depth cue
  • Stereopsis: lateral (horizontal binocular disparity) difference between the fixated and nonfixated object
    • allows visual system estimate what degree the object is removed from the horopter
  • Is automatic or preattentive (basic feature of visual perception)
29
Q
  • Fixating at the center ball, the observer is
    • able to judge the relative distances of the three balls even if monocular cues (size, interposition) are eliminated
  • Light rays eminating from the distant ball strike the retinas nasal to the foveas, giving rise to retinal disparity
  • Uncrossed disparity - images from nasal to the foveas = ball is further
  • Crossed disparity - images form temporal to the foveas = ball is closer
A
30
Q

Stereoposis (Retinal disparity): The binocular system processes ____ _____. (Tells us if the object is closer or further away from us compared to other objects)

A
  • Relative Disparity NOT absolute disparity (not absolute position of the object)
  • Stereopsis is very important contributor to depth perception at near distances not so much for far objects
  • The threshold for retinal disparity requires such objects to be separated by great distances
  • Small disparity = fusion (stereopsis)
  • Large disparity = physiological diplopia
31
Q

_____ is the most robust depth cue

What does the stereopsis test tests for?

A

Stereopsis

  • Stereopsis is achieved automatically without conscious effort (preattentive)
    • Ex. Stereo-circles pop out quickly without effort
  • Stereopsis test: tests for suppresion
32
Q

Which distance is crossed vs uncrossed (nearer/farther) and they lie on which side of the retina? (Temporal/nasal)

A
  • Farther/nearer determined by relative image displacement OD/OS
  • Nearer (crossed disparity) = images on temporal retina
  • Farther (uncrossed disparity) = image on nasal retina (relative to fixation)
33
Q

Convergence

A
  • Convergence is the weakest binocular depth cue
  • Degree of convergence can influence perceived distance & size
    • Ex. Judge distance by how much one converges (level of innervation for convergence)
34
Q

What is the SILO effect? (Convergence)

A
  • SILO effect - measurement of pt ranges of convergence & divergence
    • smaller = in
    • larger = out
  • SILO effect refers to the presumed change of the perceived size of a test object that a patient experience, while maintaining fusion when convergence or divergence is varied (Prism effect in new glasses)
    • Increased convergence = BO prisms (plus lenses), object may appear to become smaller & nearer
    • Increased divergence = BI prisms (minus lenses), object may apper larger & further
35
Q

When will you experience SILO effect?

A
  • SILO effect - prism effect in new glasses and adjustment to new glasses
    • Natural consequence of size constancy
    • Pt need to be cautioned with new glasses
    • The response is used in visual therapy as a feedback mechanism to pt about their performance
    • In general the visual system is poor at using convergence cues, but as with SILO effect can modify our judgement
36
Q

Describe SOLI effect

A
  • Smaller OUT; Larger IN
  • Opposite of SILO effect can happen
  • Due to subject prior experience that near objects are larger
37
Q

Why is vergence important? Describe micropsia & macropsia.

A
  • Vergence is necessary to our ability to process large absolute disparities
  • useless for small disparities
  • Micropsia - objects look smaller w/ prism = causes smaller object appearances as if further away,
  • Macropsia - objects look larger w/ prism = laerger object appears closer
  • Long term adaption can improve this effect
38
Q

Define relative depth

A
  • comparison of relative distance between objects (which one is closer & which one is farther away)
  • Stereopsis is a relative measurement !!
39
Q

Define relative disparity

A
  • encoding the realtive depth between objects as the difference between the absolute disparities of the 2 objects
40
Q

Stereopsis is a ____ measurement

A
  • Stereopsis is a relative measurement
  • Absolute depth/Absolute disparity = difference in angular distance from the fovea in 2 eyes
  • Relative depth/Relative disparity = differences in angles subtended in object space (a relative to b)
  • The binocular visual system processes relative disparity NOT absolute disparity
  • Binocular disparity does not tell us the absolute position of any particular object
41
Q

Define orientation disparity

A
  • Orientation disparity - differences in the orientation of targets presented to each eye might yield a percept of depth (results from gradual change in horizontal disparity)
  • Diffrequency - phenomenon where stereoscopic tilit* (percept) is created by 2 sine wave grating targets

Binocular Vision (8 decks)

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