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Chapter 6

PSYB51H3 Chapter Notes - Chapter 6: Arthropod Eye, Esotropia, Stereoscope


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
6

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Chapter 6: Space Perception and Binocular
Realism: a philosophical position arguing that there is a real world to sense.
Positivism: a philosophical position arguing that all we really have to go on is the evidence of
the senses, so the world might be nothing more than an elaborate hallucination.
Euclidean: referring to the geometry of the world.
Names in honor of Euclid, the ancient Greek geometer of the third century BCE.
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, and so forth.
The geometry of retinal images of the world is decidedly non-Euclidean.
Becomes non-Euclidean when the 3D world is projected onto the curved, 2D surface of the
retina.
Binocular: with two eyes.
Monocular: with one eye.
Probability summation: the increased detection probability based on the statistical advantage of
having two (or more) detectors rather than one.
Binocular summation: the combination (or summation) of signals from each eye in ways that
make performance on many tasks better with both eyes than with either eye alone.
May have provided the evolutionary pressure that first moved eyes toward the front of some
animals’ faces.
Binocular disparity: the differences between the two retinal images of the same scene.
Disparity is the basis for stereopsis, a vivid perception of the 3-dimensionality of the world that is
not available with monocular vision.
Stereopsis: the ability to use binocular disparity as a cue to depth.
Stereopsis is not a necessary condition for depth perception.
Monocular Depth Cue: a depth cue that is available even when the world is viewed with one eye
alone.
Binocular Depth Cue: a depth cue that relies on information from both eyes.
Stereopsis is the primary example in humans, but convergence and the ability of two eyes to see
more of an object than one eye sees are also binocular depth cues.
Occlusion: a cue to relative depth order in which, for example, one object obstructs the view of
part of another.
Most reliable of all depth cues.
Nonmetrical Depth Cue: a depth cue that provides information about the depth order (relative
depth) but not depth magnitude.
E.g., his nose is in front of his face.
Metrical Depth Cue: a depth cue that provides quantitative information about distance in the
third dimension.
Projective geometry: the geometry that describes the transformations that occur when the 3D
world is projected onto a 2D surface.
E.g., parallel lines don’t converge in the real world, but they do in the 2D projection of that
world.
E.g., a shadow is a projection onto a surface
Relative Size: a comparison of size between items without knowing the absolute size of either
one.
Texture Gradient: a depth cue based on the geometric fact that items of the same size form
smaller images when they are farther away.
An array of items that change in size smoothly across the image will appear to form a surface
tilted in depth.
Smaller objects are interpreted as farther away.
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Relative Height: as a depth cue, the observation that objects are at different distances from the
viewer on the ground plane will form images at different heights in the retinal image.
Objects farther away will be seen as higher in the image
Familiar Size: a depth cue based on knowledge of the typical size of objects like humans or
pennies.
Relative Metrical Depth Cue: a depth cue that could specify, for example, that object A is twice
as far away as object B without providing information about the absolute distance to either A
or B.
Absolute Metrical Depth Cue: a depth cue that provides quantifiable information about
distance in the third dimension.
E.g., his nose sticks out 4 cm in front of his face.
Familiar size could be an absolute metrical depth cue.
Haze (Aerial Perspective): a depth cue based on the implicit understanding that light is
scattered by the atmosphere.
More light is scattered when we look through more atmosphere.
Thus, more distant objects are subject to more scatter and appear fainter, bluer, and less
distinct.
Linear Perspective: a depth cues based on the fact that lines that are parallel in the 3D world
will appear to converge in a 2D image.
Vanishing point: the apparent point at which parallel lines receding in depth converge.
Pictorial Depth Cue: a cue to distance or depth used by artists to depict 3D depth in 2D
pictures.
Anamorphosis (or 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 with a mirror
that counters the distortion.
E.g., a picture of a picture
Motion Parallax: an important depth cue that is based on head movement.
The geometric information obtained from an eye in two different times is similar to the formation
from two eyes in different positions in the head at the same time.
When you change your viewpoint while moving (your head), objects closer to you shift position
more than objects farther away.
Motion parallax only works if the head is moving.
E.g., looking out the window of a moving train looking at a flower, cow, and tree.
Optic Flow: the pattern of apparent motion of objects in a visual scene produced by the relative
motion between the observer and the scene.
Accommodation: the process by which the eye changes its focus (in which the lens gets fatter as
gaze is directed toward nearer objects).
Convergence: the ability of the two eyes to turn inward, often used in order to place the two
images of a feature in the world on corresponding locations in the two retinal images (typically
on the fovea of each eye).
Convergence reduces the disparity of that feature to zero (or nearly zero).
Eyes converge as we shift from a far to a near point.
α gets larger.
Used more than accommodation.
Divergence: the ability of the two eyes to turn outward, often used in order to place the two
images of a feature in the world on corresponding locations in the two retinal images (typically
on the fovea of the eye).
Divergence reduces the disparity of that feature to zero (or nearly zero).
Eyes diverge as we shift from a near point to a far point and lens is thin.
α gets smaller.
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