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PSYB51 text chapter 6.docx

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Matthias Niemeier

Space Perception and Binocular Vision 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 sense, so the world might be nothing more than an elaborate hallucination Euclidean-> referring to the geometry of the world, so named in honor of Euclid, the ancient Greek geometer of the third century BCE. o 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 o The geometry of the real world, if assuming that there is a real world to perceive Monocular-> to see with only one eye Binocular-> to see with both eyes 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 Binocular Disparity-> the differences between the two retinal images of the same scene o Disparity is the basis for stereopsis, a vivid perception of the three- dimensionality of the world that is not available with monocular vision Stereopsis-> the ability to use binocular disparity as a cue to depth Monocular Cues to Three-Dimensional Space Depth cues-> information about the 3 dimension (depth) of visual space o depth cues may be monocular or binocular Monocular depth cues-> 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 o stereopsis is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye 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 object Nonmetrical depth cue-> a depth cue that provides information about the depth order but not the depth magnitude Metrical depth cue-> a depth cue that provides quantitative information about distances in the third dimension Projective geometry-> in the 3D world: the geometry that describes the transformations that occur when the 3D world is projected onto the 2D surface o Example: parallel lines do not converge in the real world, but they do in the 2D projection of the world o Describes how the world is projected 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 o An array of items that change in size smoothly across the image will appear to form a surface tilted in depth Relative height-> as a depth cue, the observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image o 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 3 dimension. Ex. His nose sticks out 4 cm in front of his face Aerial perspective (or haze)-> a depth cue based on the implicit understanding that light is scattered by the atmosphere o More light is scattered when we look through more atmosphere o Thus more distant objects are subject to more scatter and appear fainter, bluer, and less distinct Linear Perspective-> a depth cue 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 o The rules of the linear perspective are pushed to the extreme in which the projection of three dimensions into two creates a picture that is recognizable only from an unusual viewpoint o The results are known as ‘anamorphosis art’ Motion parallax-> an important depth cue that is based on head movement o The geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time Accommodation-> the process by which the eye changes its focus o The eye gets fatter as gaze is directed toward the nearer objects Convergence-> the ability of the two eyes to turn inward often used to place the two images of a feature in the world on corresponding locations in the two retinal images o Convergence reduces the disparity of that feature to zero Divergence-> the ability of the eyes to turn outward, often used in order to place the two images of a feature in the in the world on corresponding locations in the two retinal images o Divergence reduces the disparity of that feature to zero Binocular Vision and Stereopsis Corresponding retinal points-> a geometric concept stating that points on the retina of each eye where the monocular retinal images of a single object are formed are at
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