5. Steropsis and Depth Perception Flashcards
what is depth perception based on
multiple cues, each of which can sitmulate depth perception by themselves
what is a depth cue
a feature of the ocular images which changes w/ object depth
how are depth cues categorized in
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)
what are monocular depth cues
- visual angle cues
- known size, looming, perspective, texture gradients - contrast cues
- contrast, aerial perspective, overlay, shadows and shading - motion cues
- motion parallax, knetic depth effect
what does absolute depth tell the observer
how are they judged
what are they analogous to
tells the oberver how far objects are from themselves or form other objects
- judged in absolute units of distance
- analogous to egocentric direction
what are the absolute depth cues
- known size
- stereopsis based on both horizontal and vertical disparity
- convergence registration
what information is required for visually guided motion
absolute depth info
what does relative depth tell the observer
what are they judged as
what are they analogous to
tells the observer about relative order and proportion in depth
- judged as % diff or as depth ratios
- analogous to oculocentric direction
what are relative depth cues
stereopsis when based only on horiz disparity
-all cues that aren’t aboslute cues
how are all these depth cues put together for a single depth perception
- each relative depth cue is first promoted to absolute depth
(oculocentric to egocentric) - absolute depth cues are averaged by weight (strength in environment)
why do we have so many depth cues
reliability
why does stero not equal awareness of convergence
convergence creates a separate depth cue called “convergence registration” or “convergence corollary discharge”
-stero creates depth even when the eyes are fixed
what is the main stimulus to stereo
horizontal relative disparity
a single absolute disparity doesn’t stimulate stereopsis..what does
2
the approx formula for real depth shows that stero depth stimulus is proportional to…
- the physical depth interval btwn compared objects
- interpupillary dist
- larger pd=stero depth more easily - inverse square of viewing distance
- 1/2 viewing dist, stero stimulus quadruples
what is the projected depth
horiz relative disparity ay also be created by artificial lateral displacement of the ocular images in diff directions
what are some projected depth methods
- wheatstone and brewster steroscopes
- vectograms and red/green anaglyphs
- rapid alternating img projection
- free fusion and autostereograms
what depth methods do 3D movies
projected depth methods
stereoscopes are a type of _____ that present stereo images
haploscope
-devices that allow independent stimulation of each eye
what are vectograms and R/G anaglyphs
stereoscopes w/o lenses or mirrors
what are advantages to vectograms and R/G anaglyphs?
disadvantages?
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
what are the advantages/disadvantages of free fusion
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
what is the principle of autostereograms
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
what are the types of autosterograms
lenticular displays
parallax barrier displays
what are the advantages/dis of autostereograms
ad: allows stereoscope viewing w/o special glasses or stereoscope optics
disad: limited head position range in physical space
why is horizontal relative disparity only a relative depth cue
bc relative disparity alone is ambiguous about absolute depth
how does vision ocnvert horiz relative disparity into absolute depth
by promoting horiz relative disparity by way of known size, vertical disparity, and convergence registration
what is vertical disparity
stimulation of noncorresponding points in the vertical dimension of the retinas
what causes vertical disparity in normal viewing
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
why is veritcal disparity visually useful to vision
it is monotonically related to absolute depth
what are the limitations of the verticla disparity cue
- needs large stimuli and large visual field
2. slow perceptual process: better in static vision
what is convergence registration
the ability to sense convergence angle, and use that info for depth perception
what are convergence registrations 2 roles in vision
- absolute depth cue (1:1 relationshipof abs depth to convergence)
- promotes relative disparities into absolute depth
when does convergence registration work best
in near vision, like stereopsis
what is convergence micropsia
convergence causes the perceived retinal image to shrink, divergence causes it to grow
what is convergence micropsia neurally linked to
convergence innervation
when is convergence micropsia very visible during
prism vergences
what is convergence micropsis’s possible role in normal vision
a contributor to size constancy
what is SILO
small-in/large-out
- small and large refer to perceived size
- in and out refer to perceived distance
how does SILO work
convergence micropsia caues the perceived size change
convergence registration causes the perceived distance change
what can SOLI occur
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
what are preattentive image features
those that reveal a pattern even when you are not attending them
- color and motion
- stereopsis
- seem to pop out
attentive image features require what to recognize a pattern based o nthem
attentive fixation
-these include patterns defined by contour orientation, angles, curvature, etc
what is the significance of preattention in stereo
patients who have good stereo do not study a stereogram to see the depth bc depth will pop out to the patient
why does threshold stereo require more foveal viewing time
bc the disparities are tiny, cuases judment delays
what is patent stereopsis
what is it associated w/
compelling sense of depth
- proportional to disparity
- assoicated w/ single vision and smaller disparities
what is qualitative stereopsis
what is it associated w/
uncertain depth
- objects are much nearer or farther than fixation
- amount of depth unclear
- associated w/ diplopic images and larger disparities
what are the 2 parallel neural pathways from retina to visual cortex
parvo and magno
