PSYB51H3 Chapter Notes - Chapter 6: Aerial Perspective, Vanishing Point, Horopter
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Chapter 6 –Space Perception and Binocular vision
The ability to perceive and interact with the structure of space is one of the fundamental
goals of the visual system.
Realism: A philosophical position that there is a real world to sense.
Positivism : a philosophical position that all we have to go on is the evidence of our senses,
so the world might be nothing more than an elaborate hallucination .
Euclidean: named in honor of Euclid
The geometry of real world is Euclidean.
Parallel lines remain parallel as they are extended in space, objects maintain their size and
shape in the real world.
BUT, Euclidean geometry is not the only geometry, the geometry of retinal images of that
The geometry becomes non-Euclidean when the D world is projected onto the curved 2D
surface fo teh retina. Parallel lines in the world donot remain parallel in the retinal
iamge.teh retinal area occupied by an object gets smaller as the object moves further
away---- if we want to appreciate the Euclidean world, we have to reconstruct it from non-
We reconstruct teh world from 2 non-Euc inputs: teh two distinct retinal images.
Teh two retinal images always differ. They differ because the retinas are in different
places.i.e just as u and the person next to u sees different views of the world.
Why have two eyes?
-same evolutionary advantage as having two kidneys, lungs etc you can lose one eye and
still be able to see.
-doubling the number of eyes is that they enable u to see more of the world.
Our visual field is limited to 190 deg from L to R. 110 is covered by both eyes.
Field is more restricted vertically: 60 deg up an d 80 deg down.
Overlapping binocular visual field give predators a better chance to spot small, fast-moving
Binocular summation: the combination of signals from each eye in ways that make
performance on many tasks better with both eyes than with one
-may have caused the evolution of eyes infront of faces.
Another benefit for overlapping binocular fields : Binocular disparity
b. disparity :
-the differences between the two retinal images of the same scenes.
-is the basis for vivid perception of 3 dimensionality of the world , which is not available
with purely monocular vision
Stereopsis – binocular perception of depth
Monocular = one-eyed vision
-Loss of stereopsis
But stereopsis is not necessary for depth perception but it does add a richness to teh
perception of 3D world.
Monocular Cues to 3D space
M.C Escher- Relativity picture
Each bit of stairway uses cues that allow us to infer 3D from 2 but when we follow
the stairs, the drawings cleverly fails to form a coherent representation.
Even when no one is trying to fool us, its hard to reconstruct faithfully the
Euclidean image from non-Euc input. we must use depth cues!
Every view of the world provides multiple depth cues. The cues may reinforce each
other or be contradictory.
1.Occlusion-gives information about the relative position of objects
Present in almost every scene
Most reliable as some argue
Wrong only in accidental viewpoints
Is a nonmetrical depth cue: just gives us the relative orderings of
occluders and occludes
metrical depth cue- provides information about distance in 3D.
2.Size and position cues- the image on the retina formed by an object out in the
world gets smaller as the object gets further away. projective geometry
The visual system knows projective geometry implicitly
Describes how teh world is projected on to a surface.
All else being equal, smaller things are farther away.
Relative size: a comparison of size between items without knowing
teh absolute size of either one.
Texture gradient: a depth cue based on the geometric fact that
items of same size form smaller images when they are farther away.
The ability to perceive and interact with the structure of space is one of the fundamental goals of the visual system. Realism: a philosophical position that there is a real world to sense. Positivism : a philosophical position that all we have to go on is the evidence of our senses, so the world might be nothing more than an elaborate hallucination . Parallel lines remain parallel as they are extended in space, objects maintain their size and shape in the real world. But, euclidean geometry is not the only geometry, the geometry of retinal images of that world is non-euclidean. The geometry becomes non-euclidean when the d world is projected onto the curved 2d surface fo teh retina. We reconstruct teh world from 2 non-euc inputs: teh two distinct retinal images. They differ because the retinas are in different places. i. e just as u and the person next to u sees different views of the world.