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Vision Science 5 > Lecture 7/8 > Flashcards

Lecture 7/8 Flashcards

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1
Q

what are the 6 pictorial monocular depth cues?

A

relative size, linear perspective, texture gradient, aerial perspective, lighting and shading, and interposition

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2
Q

what are the 3 non-pictorial monocular depth cues?

A

accommodation, motion parallax and kinetic depth effect

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3
Q

what is relative size?

A

retinal image size is inversely proportional to distance - requires some knowledge about the object

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4
Q

what are 2 things that can cause a decrease in retinal image size?

A

object size remains constant but distance increases or distance remains unchanged but the object shrinks

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5
Q

what is size constancy?

A

the perceived size of an object remains relatively constant even if it’s retinal image size changes

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6
Q

what is shape constancy (form constancy)?

A

the perceived shape of an object remains relatively constant even if the actual retinal image shape changes, due to changes in viewing angle

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7
Q

what is Emmert’s law?

A

a projected after-image or eidetic image is altered in size proportion to the distance of the surface on which it is projected

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8
Q

what is the moon illusion?

A

the moon appears smaller in the zenith (sky) than at the horizon even though the physical distance is constant

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9
Q

what is linear perspective?

A

perception of parallel lines or edges converging towards a distant vanishing point at the horizon (based on size constancy principle)

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10
Q

what is texture gradient?

A

distant objects are seen as more densely packed (relates to size principle)

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11
Q

what is aerial perspective?

A

distant objects appear less sharp than near objects due to scattering of light

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12
Q

how is lighting and shading a monocular depth cue?

A

the shadow of an object is interpreted as falling behind an object

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13
Q

what is interposition?

A

the obstruction of the view of a distant object by a closer object

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14
Q

how is accommodation a monocular depth cue?

A

more accommodation innervation is needed for viewing a closer object (weak depth cue)

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15
Q

what is motion parallax?

A

viewing a scene while moving, the relative position of objects change depending on their locations relative to the fixation point:
objects closer to fixation = against movement
objects further = with movement

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16
Q

what is the kinetic depth effect?

A

the flat image of a rotating object acquires a strong perception of 3D depth because of the motion in the image (related to motion parallax)

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17
Q

what are the 2 binocular depth cues?

A

convergence and stereopsis

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18
Q

what happens to the perceived image with increased convergence by BO prisms?

A

the perceived image appears to get smaller and closer

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19
Q

what happens to the perceived image with increased divergence by BI prisms?

A

the perceived image appears to get larger and farther away

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20
Q

why does the converging image that is closer in the vectogram appear smaller?

A

in order to maintain size constancy it must be perceived as smaller than the original

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21
Q

what is convergence micropsia?

A

SILO = small in and large out

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22
Q

what is SOLI?

A

small out and large in = small portion of observers report this instead of SILO (related to patient’s expectations)

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23
Q

what is stereopsis?

A

a perception based mainly on horizontal relative binocular disparity

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24
Q

what is absolute depth perception?

A

tells the observer how far objects are from themselves or other objects (distance from object to egocenter in meter, feet, etc.)

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25
Q

what is relative depth perception?

A

tells the observer about the comparison of depth (judged in % difference or by depth ratio)

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26
Q

what is absolute disparity?

A

the difference in the external longitudinal angles subtended by an object at each eye

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27
Q

what is absolute depth determined by?

A

absolute disparity

28
Q

how do you calculate (n) the retinal disparity angle?

A

n = angle a - angle b or n= PD(delta D)/D^2

29
Q

how do you convert geometric disparity (retinal disparity) to seconds of arc?

A

use equation: n = PD(delta D)/D^2 x 206,256

30
Q

how do you clinically measure stereoacuity?

A

using the Howard-Dolman apparatus to find the minimum displacement needed to see the difference in depth

31
Q

what is the normal stereoacuity threshold in humans?

A

2-6 seconds of arc

32
Q

what happens to stereoacuity when there is a larger PD?

A

the larger the PD - the larger the disparity seen

33
Q

what happens to stereoacuity when the object is closer?

A

the closer the object - the larger the disparity seen

34
Q

what do each part of the equation: n = PD(delta D)/D^2 represent?

A

n = angular disparity
PD = interpupillary distance
D = fixation distance
delta D = depth interval

35
Q

which is more accurate for disparity - closer or further away?

A

more accurate at near than distance

36
Q

what is the geometric limit for disparity for a 10” arc stereoacuity threshold? (upper limit)

A

1320 meters or 0.8 miles (beyond this limit you don’t get depth perception from stereopsis)

37
Q

what is the stereoacuity if a patient can see 9/9 targets in the Titmus stereo fly?

A

40” arc

38
Q

what 5 things can decrease stereopsis?

A

viewing in periphery, low contrast, dim light, blue colors and short exposure time

39
Q

what is the lower limit of stereopsis?

A

stereoacuity - the smallest disparity we can detect

40
Q

what is the upper limit of stereopsis?

A

what is the largest disparity that can still give us depth sensation

41
Q

what is patent or quantitative stereopsis?

A

high quality stereopsis - the perceived magnitude of object depth is proportional to the disparity (extends slightly past Panum’s area = diplopia but patent)

42
Q

what is latent/qualitative stereopsis?

A

objects can be perceived as nearer or farther than fixation - but magnitude of depth cannot be perceived (way beyond Panum’s area = diplopia and violates Worth fusional hierarchy)

43
Q

what are 4 ways to display stereoscopic images?

A

stereoscope, anaglyph and vectogram, liquid crystal shutter stereogoggles and free fusion

44
Q

how does a mirror stereoscope work?

A

two mirrors present distinct images to each eye - the images may be dissimilar producing binocular rivalry for stereopsis (angle of mirrors can vary)

45
Q

how does a brewster refracting stereoscope work?

A

uses decentered +5 lenses to create prismatic effect (ex: keystone)

46
Q

how do anaglyph and vectogram’s produce stereopsis?

A 
anaglyph = red/green or red/blue glasses to separate eyes views
vectogram = polarized glasses
47
Q

how do liquid crystal shutter stereogoggles produce stereopsis?

A

alternating occlusion of one eye at high speed (15 Hz and higher) - displayed image is synchronized with eye that isn’t occluded

48
Q

how does free form produce stereopsis?

A

eyes need to converge/cross

49
Q

what are the 2 parallel neuronal pathways from retina to visual cortex for stereopsis?

A 
parvocellular = fine stereopsis
magnocellular = coarse stereopsis
50
Q

what is the disparity range for fine and coarse stereopsis?

A 
fine = 2" - 20'
coarse = 6' - 10 degrees
51
Q

what is the color response for fine and coarse stereopsis?

A 
fine = chromatic
coarse = black and white
52
Q

what is the retinal location for fine and coarse stereopsis?

A 
fine = mostly fovea/macular
coarse = pan retina/mostly peripheral
53
Q

what is the motion response for fine and coarse stereopsis?

A 
fine = prefer static images
coarse = prefer motion
54
Q

what is the spatial frequency for fine and coarse stereopsis?

A 
fine = prefer higher spatial frequency
coarse = prefer lower spatial frequency
55
Q

which type of stereopsis, fine or coarse is more susceptible to binocular anomalies?

A

fine stereopsis (global)(coarse can still function with small/moderate strabismus - can still take advantage of monocular cues)

56
Q

what is local stereopsis?

A

stereoscopic depth based on images that can be recognized monocularly as well as binocularly

57
Q

what is global stereopsis?

A

brain sees objects through binocular vision that it doesn’t see monocularly

58
Q

which mechanisms, fine or coarse, are performed in local stereopsis?

A

both fine and coarse

59
Q

which mechanisms, fine or coarse, are performed in global stereopsis?

A

only based on fine stereopsis

60
Q

what are 2 examples of local stereopsis testing?

A

line stereogram and eccentric circles (also worth circles in randot book and lifesaver card)

61
Q

what are 2 examples of global stereopsis testing?

A

random dot stereogram and autostereogram (“magic-eye photos”)

62
Q

which test picks up reduced stereopsis better in the clinic?

A

random dot stereogram works better - global stereopsis is more sensitive to binocular anomalies

63
Q

what is the Pulfrich phenomenon/effect?

A

temporal disparity (time delay) creates stereopsis = ND filter reduced retinal illumination and delays the neural signal

64
Q

which direction is the movement perceived if the ND filter is over the OS? what about over OD?

A 
OS = clockwise
OD = counterclockwise
65
Q

what are 2 potential causes of the Pulfrich effect?

A
  1. ay situation that has a significant difference in retinal illumination (anisocoria)
  2. optic neuropathy/neuritis affecting one eye more (glaucoma too)
66
Q

what is chromostereopsis? what 2 things cause it?

A

color induced stereopsis = caused by transverse chromatic aberrations and visual and optic axes of the eye slightly different

67
Q

what happens to blue and red colors in chromostereopsis?

A

blue light falls more nasally on retina than red and blue light creates relative uncrossed disparity(perceived as farther away)

Vision Science 5 (14 decks)

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