PSYB51H3 Chapter Notes - Chapter 6: Binocular Disparity, Visual System, Sine Wave
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CHAPTER SIX – SPACE PERCEPTION AND BINOCULAR VISION
Realism = a philosophical position arguing that there is a real world to sense.
Positivism = philosophical position arguing that all we really have to go on is the evidence of sense, so the world
might be nothing more than an elaborate hallucination.
Euclidean = refers to the geometry of world. In Euclidean geometry, parallel lines remain parallel as they are
extended in space, objects maintain the same size and shape as they move around in space, the internal angles of a
triangle always add to 180 degrees, etc.
although real world is Euclidean, geometry of retinal images of that world is non Euclidean, when the 2D world is
projected onto the curved, 2D surface of the retina. We reconstruct the world from 2 non-Euclidean inputs: the 2
distinct retinal images which are always different cuz the retinas are in slightly diff places.
We have 2 eyes cuz 2 is better than 1, also 2 eyes enable you to see more of the world, our visual field is limited to
about 190 from left to right 110 of which is covered in both eyes. Vertically is 60 degrees up from center of gaze and
Binocular summation combination of signals from each eye in ways that make performance on many tasks better
w/both eyes than one eye alone, this might be reason y our eyes moved infront.
Binocular disparity = differences b/w 2 retinal images of the same scene. stereopsis = ability to use binocular
disparity as a cue to depth. Stereopsis is not a necessary condition for depth perception or space perception, we can
see depth with one eye. But stereopsis add a richness to perception of the 3D world
Depth cue = info about the 3D of visual space. Depth cues may be mono or binocular Monocular depth cue = a
depth cue that is available even when the world is viewed w/one eye alone. Binocular depth cue = a depth cue that
relies on info from both eyes. Stereopsis is an ex
MONOCULAR CUES TO 3D SPACE---OCCLUSION
Occlusion = cue to relative depth order (position) of objects. This cue is present everywhere and is most reliable of
all depth cues except in accidental viewpoints = viewing position that produces some regularity in visual image that
is not present in the world, ie sides of 2 independent objects lining up perfectly
Nonmetrical depth cue = a depth cue that provides info about the depth order, relative depth, but not depth
magnitude (ie how much distance). Occlusion is nonmetrical depth cue. A absolute metrical depth cue is one that
does provide quantitative info about distance in 3rd dimension
SIZE AND POSITION CUES
Projective geometry = projective geometry describes the transformations that occur when the 3D world is projected
onto a 2D surface, ex parallel lines do not converge in the world, but they do in the 2D projection.
Relative size = depth cue - comparison of size /b items w/o knowing the absolute size of either one
Texture gradient = depth cue – items of the same size form smaller images when they are farther away, an array of
items that change in size across the image will appear to form a surface in depth
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Relative height = depth cue - objects at diff distances from the viewer on the ground plane will form images at diff
heights in retinal image. Objects further away will be seen as higher in the image
Multiple cues interact to produce a final perception, similar to the metaphor of perceptual committees
Familiar size = depth cue – based on knowledge of typical size of objects
Occlusion is a nonmetrical cue. Relative size and relative height cues, esp if taken together provides some metrical
info. Relative size and height can’t tell us the exact distance but they are relative metrical depth cues = depth cue
that could specify, that object A was twice as far away as B w/o providing info about the absolute distance to either
A or B. Familiar size can be absolute metrical depth cue = depth cue that provides absolute info about the distance
in the 3 dimension, if our visual system knew the actual size of the object and the visual angle of the object’s
projection on the retina, it then can calculate exact distance from object to eye, in theory but in practice, ur visual
system not know exact.
AERIAL/ LINEAR PERSPECTIVE
Aerial perspective (haze perspective) = depth cue based on the implicit understanding that light is scattered by
atmosphere. Thus, more distant objects are subject to more scatter and appear fainter, bluer and less distinct.
Linear perspective = depth cue based on the fact that lines that are parallel in 3D world will appear to converge in a
2D world, except when the parallel lines lie in a plane that is parallel to the plane of the 2D image for ex, a closed
door, the parallel edges will remain parallel but when we open the door, the base boards are not parallel. The board
will meet a vanishing point = apparent point at which parallel lines receding in depth converge. Linear perspective
provides relative metrical depth info and can be seen as a special case of relative size and height cues.
PICTORIAL DEPTH CUES AND PICTURES
Pictorial depth cues = cue to distance or depth used by artists to depict 3D depth in 2D pictures, these cues are the
ones described above.
Anamorphosis/ anamorphic projection = use of the rules of linear perspective to create a 2D image so distorted
that it looks correct only when viewed from a special angle or w/a mirror that counters the distortion
Motion parallax = 1st nonpictorial depth cue = cue based on head movement. Geometric info obtained from an eye
in 2 diff positions at 2 diff times (motion parallax) similar to the info from 2 eyes in diff positions in the head at
same time (stereopsis). Parallax refers to the geometric relationship: when your eyes move, objects closer to you shift
position more than objects farther away when you change your viewpoint. cue provides relative metrical info.
Downside of motion parallax is that it works only if the head moves, just moving the eyes back and forth not work.
ACCOMMODATION AND CONVERGENCE
Accommodation = process by which eye changes its focus (lenses gets fatter as gaze is directed toward near objects)
If we can monitor our state of accommodation and or extent to which our eyes were converged, we could use this
info as a cue to depth of the objects we were typing to bring into focus: the more we have to converge, the more lens
have to bulge, the closer it is. When we focus on objects more than 2-3m away, the lens is as thin as it can get and the
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