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81 Cards in this Set
- Front
- Back
4 advantages to having 2 frontal eyes
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1. larger field of view with central superimposition.
2. check eachother, especially if one eye is impaired 3. backup - someone pokes out one eye 4. stereopsis by binocular summation |
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define stereopsis
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quantitative and qualitative improvement in relative depth perception occurring w/ bv
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define: primary visual direction
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oculocentic direction of an object that is fixated along the primary line of sight and is imaged on teh center of the fovea.
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define: secondary visual direction
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oculocentric directions of other retinal image locations relaive to primary v.d.
images located left of foea are perceived right of fixation |
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define: egocentric direction
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combination of oculocentric visual direction w/ info about eyeorientation in head and head position relative to body. referred to by cyclopean eye.
EOM info is included |
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McKee's laws of development (4)
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1. as children get older, they get better at things
2. whatever it is, girls do it before boys 3. everything develops w/ everything else things start out badly, then they get better, then they get worse again |
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which visual tasks develop first and when?
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2-5 months:
luminance efficiency dark adaptation absolute thereshold peak contrast sensitivity |
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which visual tasks develop later on in development? why?
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grating acuity
vernier acuity. require higher acuities |
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how do we test children's thresholds in visual tasks? (2)
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forced-choice preferential looking
visual-evoked potential |
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what is interesting about acuities taken by VEP?
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infant's brain is able to ersolve gratings that the infant is unable to respond to; may be a behavioral immaturity
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What 3 changes occur in the retina in developing infants?
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1. foveal cones become thinner and more elongated
2. migration of ganglion cells and inner nuclear cells 3. formation of foveal pit, higher cone density in central foveal region |
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what is acuity development limited by in early development?
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NOT "front end." more likely cortical connections
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what is contrast sensitivty limited by in early development?
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not front end either! high spatial acuities develop slow and later, low spatial frequencies develop faster
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what is the nature of stereopsis development?
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sudden, around age 2-4
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what is the nature of stereoacuity develoment?
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sometime age 4 and up.
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what can interfere w/ stereopsis?
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1. abnormal eye alignment
2. immaturity of disparity sensitive neurons in V1 |
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what kind of eye alignment do neo-nates have?
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mostly exo in sleep, and awake, in the first 2 months, might have intermittent mis-alignment
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when do infants become orthotropic?
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3 months
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T/F newborn infants can converge to track an approaching target
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T, but they wont' be accurate and consistent until 3-4 months
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T/F convergence must be very accurate in order to detect coarse disparities
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F
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T/F within the first week of life, infant monkeys have the sampe proportion of phase-disparity sensitive neurons as adults do in the primary visual cortex
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T
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Why are newborns blind to disparity if they have a lot of phase-disparity sensitive neurons?
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extraction of relative disparity takes place beyond V1, possibly in V2. and/or, V1 neurons are immature
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How can V1 neurons be immature
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1. do not have adult sensitivity
2. less responsive overall than adult neurons 3. show more interocular suppression than in adults |
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what age group has a high prevalence of large refractive errors?
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newborns
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by what age do most children become emmetropic?
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2-3 yrs
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what is considered high hyperopia?
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>3.5 D
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what predicts amblyopia/strabismus later in life and at what age?
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high hyperopia at around 6 months
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what are risk factors for amblyopia later in life when seen at children at __age
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1. persistent anisometropia
2. high hyperopia at 6 months 3. abnormal refractive error at age 1 4. strabismus 5. deprivation (small percentage of amblyopes) |
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are you mokre likeley to be an anisometrope if you are a myopic anisometrope or hyperopic? why?
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hyperopic. accommodation is yoked, so one eye's image ill always be blurry
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who is more likely to develop less stereoacuity?
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myopic anisometropes
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where in your brain do you get infromation from both eyes? in what structures?
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V1 visual cortex, ocular dominance columns. fully formed at birth
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2 concepts of worth and chevasse that affect abnormal visual development
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a. obstacles to normal visual development (strabismus, anisometropia, cataract, monocular occlusion)
b. critical periods for visual development (arrest v. extinction) |
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what kinds of problems can strabismus lead to?
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1. diplopia
2. confusion 3. suppression 4. loss of binocular neurons in cortex |
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does amblyopia occur because of disuse or binocular competition/interactions?
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competition!
when you lesion one eye, it affects cortical areas w/ bino input more than monocular input cortical areas |
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what is Hubel and Wiesel's hypothesis about competition for synaptic space?
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your two eyes compete for in in the visual cortex, and the nondeprived eye wins
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what are 2 kinds of hebbian synapses?
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long-term potentiation, and long term depression
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Where is the damage done in amblyopia?
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the primary visual cortex (V1) and possibly in other visual areas
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in amblyopia, is normal visual development arrested or extinguished?
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both! when deprivation occurs at a younger age (less than 1 yrs old) arrest at steady 0. when it occurs after 1, it extincts to a lesser level and arrests there (not necessarily at 0)
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does steropsis arrest or extinct in development?
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extinct (especially with esotropic infants)
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what is the critical period according to Hubel and Wiesel?
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shifts in ocular dominance determine path of amblyopia. critical period in calts 4-12 weeks, monkeys 1-12 wks. up to 3-4 months, you can reverse it
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what is the evidence of multpile critical periods?
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1. in monkeys, sensitive period is shorter in input layer than in other layers of V1.
2. different psychophysical functions affected by lid suture at different times 3. lid suture at 3-6 months had influence on spectral sensitivity and abolished pattern and bv 4. lid suture at 25 months had no affect on spectral sensitivity but redecued contrast senstivity at high spatial frequencies, reduced binocular summation 5. lid suture beyond 25 months disrupted binocular functioning (but did not affect contrast sensitivity) |
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how long is crtical period in humans?
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bino connections are vulnerable during first 18 months of life, susceptible to effects of strabismus until at least 7 yo
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what is the relationship of deprivation to development?
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mirror image: those visual functions that develop last are most at risk and susceptible for the longest time
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can the critical period be prolonged?
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having a slip up in strabismus after onset of steropsis makes more problems than before onset, so treatment should happen before stereopsis develops. drugs? periods of bv?
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define amblyopia
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reduced visual acuity in otherwise normal eye
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what is crowding?
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a letter that is easily recognized on its own is unrecognizable if surrounded by other letters (even when focusing on that letter)
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what is crowding like for amblyopes?
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in the ambloyopic fovea, crowding extends over long distances, distinct from ordineary masking
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what is contrast sensitivity like for amblyopes?
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high levels of internal noise - very bad at vernier acuity tasks
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what are the trends we see for different kinds of amblyopes?
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mostly non-binocular amblyopes (strabismics mostly) have higher sensitivities and lower acuities. binocular amblyopes - higher acuities, lower sensitivities
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Where in the brain does amblyopia do it's damage?
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primary visual cortex and possibly other areas as well. we see reduced response to high spatial frequencies in deprived eye
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T/F behavioral losses are larger than physiological losses in amblyopes
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T
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what does it mean if behavioral losses are greater than physiological losses in amblyopia?
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there are levels beyond V1 that are affected
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what are some current theories about how amblyopia occurs?
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reduced sensitivity of small receptive fields in the fovea, cortical undersampling, topographical jitter
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what are some higher order deficits associated with amblyopia?
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1. increased cortical noise
2. second-order texture 3. feature integration 4. counting |
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how do amblyopes respond when asked to count quickly flashing dots?
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always underestimate
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why cant strabismic amblyopes count accurately?
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high level limitations: limits in amt of info the amblyopic visual ysstem cn attend to and individuate
when asked to count missing patches, they underestimate the number of missing patches as WELL as number of patches. |
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What are the primary forms of treatment for children w/ amblyopia
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1. optical correction
2. patching 3. penalization 4. active treatment 5. experimental treatment |
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How long should you patch a pt?
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1 yo: <1hr/day
2 yo 2hr/day 3 yo 3hr/day... no mroe than 6 hrs, otherwise you risk occlusion amblyopia |
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what experiment shows plasticity in adult amblyopes?
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patients with AMD show improving VAs in the fellow eye as the degenerating eye worsens
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what are 2 forms of active treatment of amblyopia?
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videogames and perceptual learning
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what visual tasks can an amblyope improve with perceptual learning?
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venier acuity. some amblyopes translate learning to snellen, others, learning is specific to the task
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T/F: monocular defous has a big effect on decreasing numbers of simplex and complex neurons, but not as much as suturing
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T
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what effect does suppression have on input info to V1?
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suppression! have less bino. ocular dominance columns than monocular ones, so as soon as you switch to binocular cues, you suppress one eye.
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Are cortical receptive fields binocular or monocular and what does this mean?
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binocular. info from the two eyes converge i neurons in the striate cortex, can be asymmetric input
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what is selective adaptation in the visual cortex?
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neurons of a certain "tilt" fatigue, so afterwards, profile of neuronal sensitivity changes
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how long is the sensitive period in humans?
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binocular connections vulnerable during first 18 onths of life and are susceptible to strabismus until at least 7 years
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How ca intervention push development system back into a plastic state?
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1. by removing structural brakes
2. resetting E-I balance/feedback signaling..? 3....see Fluoxetine: restores plasticity in adult visual cortex. it increases expression of brain-derived neurotrapic factor in adult rats that were monocularly deprived in critical period |
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What are 6 factors that can influence stereoacuity?
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1. distance from horopter (fixation disparity)
2. retinal eccentricity 3. target separation (disparitygradients and sequential stereopsis) 4. spatial frequency 5. differences in ocular cotnrast-aniso blur 6. exposure duration and interocular delays |
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How does increasing retinal eccentricity affect stereoacuity?
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worse stereoacuity
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How does moving off horopter affect stereoacuity?
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the further you are from horopter, the worse your stereoacuity is
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Explain the Pulfrich effect
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when you put a ND filter over one eye, you reduce the amount of light entering tha teye. this slows down neural transmission time from the retina to the cortex, so that eye's stimulus gets to the cortex later than the other eye''s stimulus.
we interpret this as a change in space. it looks closer when it swings to eye w/ filter, and looks farther when it goes away from the filtered eye |
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explain the effect of spatian frequency on stereoacuity
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the effect of dimming luminance and contrast on stereoacuity is greater for higher than lower spatial frequencies. the effects of asymmetric defocus is more than bilateral defocus (in decreasing stereoacuity)
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what are 4 percepts that are associated w/ sensory fusion w/in panum's fusional area?
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1. haplopia
2. accurate sense of egocentric direction 3. color fusion 4. luster |
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what are four factors influencing panum's fusional area?
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1. disparty dynamics (rate of change), more movement, smaller fusion ranges
2. disparity gradient (spatial crowding), things close together interfere w/ eachother's fusion 3. spatial frequency (size) - larger objects, larger fusion ranges. coarse detail, larger fusion range. 4. retinal eccentricity, larger ecc., larger fusion |
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what is the maximum disparity gradient you could get?
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2
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how do yu calculate disparity gradient?
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ratio of deth/separation by direction
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when do you see spatial crowding in rael life?
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tree foliage. you can't see leaves singly when fixating somewhere else.
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why do we have stereopsis?
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1. predation. when you stop moving, compensates for motion parallax
2 tool manipulation 3. |
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TF retinal disprity is oculocentric
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T
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TF stereodepth is headcentric.
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T
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constraints on stereopsis
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smoothness constraint
uniqueness similarity |