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PSYB51H3 (301)
Chapter 6-11

PSYB51 Midterm 2 Detailed chapter notes (Chapter 6-11)

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University of Toronto Scarborough
Matthias Niemeier

Chapter 6: 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 senses, the world may be nothing more than an elaborate hallucination Euclidean The geology of the world, so named in honor of Euclid, the ancient Greek geometer of the third century BC E. in Euclidean geometry, parallel lines remain parallel as they are extended into space, objects maintain the same size and shape as they move around in space, the internal angles of a triangle always add to the 180 and so forth - The geometry of retinal images of the world is decidedly non-Euclidean We construct the world from two non-Euclidean inputs: the two distinct retinal images - Advantages to having two eyeballs: you can lose one eye and still be able to see, and they 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 by both eyes; 60 up from the center of gaze and 80 down Binocular visual fields just a better chance to spot small, fast-moving objects - Binocular summation the combination (or summation) of signals from each eye in ways that make performance on many tasks better with both sides with either eye alone. They have provided evolutionary pressure that first moved eyes to the front of some birds and mammals face - Binocular disparity the differences between the two retinal images of the same world. Disparity a basis for vivid perception of the three dimensionality of the world that is not available with purely monocular (one-eyed) vision. - Stereopsis the ability to use binocular disparity as a cue to depth. Not a necessary condition for depth perception or space perception - Depth cues information about the third dimension (depth) of visual space. Depth cues may be monocular or binocular. - 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 he ability of two eyes to see more of an object than one eye sees are also binocular depth cues. 1 www.notesolution.comWhen Ocular Cues to Three-Dimensional Space Occlusion - Occlusion gives information about the relative positions of objects (makes it easy to infer relative position in depth.) Present in almost every visual scene Most reliable of all depth cues - Researchers argue that it is the most reliable of all the depth cues. - Non-metrical depth cue provides information about the depth order (relative depth) but not depth magnitude (e.g. his nose is in front of his face) Example: Occlusion - Metrical depth cue provides quantitative information about distance in the third dimension Size and Position Cues - Projected geometry - the geometry that describes the transformations that occur when a three-dimensional world is projected onto a two-dimensional surface for example parallel lines do not converge in the world, but they do in the two- dimensional projection Smaller things are farther away Relative size - the 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. - 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. Objects farther way will be seen as higher in the image. For objects on the ground plane, objects that are more distant are higher in the visual field Texture fields that provide an impression of three-dimensionality are really combinations of relative size and relative height cues provide metrical information Do not tell the exact distance to an object or between objects - Familiar size a depth cue based on knowledge of the typical size of objects like humans or pennies. - Occlusion is a non-metrical cue, providing only depth order. - Relative metrical depth cue a depth cue that could specify that object 1 was twice as far away as object 2 without providing information about the absolute distance - Absolute metrical depth cue a depth cue that provides absolute information about the distance in the third dimension (e.g. object 1 is 4cms in front of object 2) Haze Aerial Perspective - Relies on an implicit understanding that light is scattered by the atmosphere, and 2 www.notesolution.com that more light is scattered when we look through more atmosphere. - More distant objects are subject to more scatter and appear fainter and less distinct - Short wavelength (blue) are scattered more than medium and long wavelength Linear Perspective - Based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image - When the parallel lines lie in a plane that is parallel to the plane of the two- dimensional image, the parallel lines will not appear to converge. - Linear perspective provides relative metrical depth information. - Vanishing point - apparent point at which parallel lines receding in depth converge Pictorial Depth Cues and Pictures - Pictorial depth cue cue to distance or depth used by artists to depict three- dimensional depth in two-dimensional pictures. - When image is viewed from the correct position, the retinal image formed by the 2D picture will be the same as the retinal image that would have been formed by the 3D world, and hence we see depth in the picture. - To correctly interpret the shape of three-dimensional objects from two-dimensional pictures, people take the orientation of the flat surface of the image into account so that they can understand both that the picture is, in fact, a picture and at the same time, calculate an accurate impression of the thing that is portrayed - Our visual system compensates for the perceptual distortion in the first picture, or the context enables us to take the orientation of the surface and account page 143 - Anamorphosis (Anamorphic projection) use of the rule of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion. Motion Cues - Motion parallax an important depth cue that is based on head movement. 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. Parallax geometric relationship: when your eyes move, objects closer to you shift position more than objects farther away when you change your viewpoint - The geometric information obtained from an eye in two different positions at two different times (motion parallax) is similar to the information by two eyes in different positions in the head at the same time (stereopsis). relative metrical information of how far away objects are - The downside of motion parallax is that it works only if the head moves Accommodation and Convergence - The human eye focuses via a process called accommodation, in which the lens gets fatter as we direct our gaze toward nearer objects; and convergence , refocusing by 3 www.notesolution.com
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