PSYB51 ch6 notes

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Matthias Niemeier

PSYB51- CHAPTER 6 – SPACE PERCEPTIONAND BINOCULAR VISION Euclidean: the geometry of the world. In here the parallel lines remain parallel when they are extended in space, objects maintain the same size and shape as they move around in space, and internal triangles add up to 180 degrees. However the retinal area occupied by an object gets smaller as the object moves further away from the eyeballs. What this mean is that if we want to appreciate the Euclidean world, we must reconstruct it from the non-Euclidean input (2D surface of retina). - The geometry of retinal images of that world is decidedly non-Euclidean - The geometry becomes non-Euclidean when the three dimensional world is projected onto the curved, two-dimensional surface of the retina - Having two eyes is an evolutionary advantage – you can lose one and still see - Having two eyes enable you to see more of the world - Human visual field is limited to about 190 degrees from left to right, 110 degrees of which I covered by both eyes - Binocular visual fields give predator animals a better change to spot small, fast-moving objects in front of them that might provide dinner - Binocular: having two eyes Binocular summation: the combination of signals from each eye that makes performance better vs one eye. Binocular disparity: the difference between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the 3D of the world that is not available with monocular vision. Stereopsis is the ability to use binocular disparity as a cue to depth.Aphase difference between the two monocular gratings creates binocular disparity and some cells in the visual cortex is sensitive to this phase shift. Depth cue: information about the third dimension of visual space. Monocular depth cue: a depth cue when the world is viewed with one eye Binocular depth cue: a depth cue when the world is viewed with two eyes. Stereopsis is the primary example in humans. Occlusion: a cue to relative depth order, in which one object obstructs the view of another. It’s a nonmetrical depth cue. Nonmentrical depth cue: a depth cue that tells us about the depth order but not he depth magnitude. Metrical depth cue: tells us about the quantitative information about distance in third space. Projective geometry: it’s a geometry that tells us about the changes that occur when the third dimensional world is projected in to two dimensional surface. The parallel lines in 2d world can converge Relative size: a comparison of sizes between items without knowing the absolute size of either one. Texture gradient: a type of depth cue that us information about the items that are the same size form smaller images when they are father away. Relative height: a depth cue that tells us information about objects at farther away will be seen as higher in the image. Objects at different distances from the viewer on the ground will form images at different heights. Rabbits in the example are the same size yet they look different this is because the rabbit at the bottom must be closer. Familiar size: a depth cue based on our knowledge of the typical size of objects. Ex. Human hand. Relative metrical depth cue: a depth cue that could specify for example when we can tell that objectAIs twice as far away as object B without knowing the actual distance to either.ex rel size and height, motion parallex Absolute metrical depth cue: a depth cue that tells us exactly how far/close something is. Ex. Familiar size. Aerial perspective/haze: a depth cue based on the understanding that the light is scattered by the atmosphere. The more distant the objects are the bluer, scattered, fainter, and less distinct they are. Linear perspective: a depth cue that tells us that lines are parallel in the 3d world will appear to converge in two dimensional image.Anamorphosis/anamorphic projection: tells us that our ability to cope with distortion is limited.Anamorphosis makes use of the linear perspective rule to create 2d image so distorted that it looks correct only when viewed from a special angle or a mirror that counters the distortion. Vanishing point: the apparent point at which parallel lines receding in depth convergence. Pictorial depth cue: a depth/distance cue used by artists to depict 3d depth into 2d pictures. Motion parallex: a depth cue based on head movement not just the moving eyes back and forth. Think of the train example. 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. Motion parallex provides relative metrical information about how far away objects are. Object closer to you shift position more quickly than objects farther away Accommodation: the process by which an eye changes its focus. The lens get fatter as we gaze towards near objects. Convergence: as we shift from a focus from far to a near point. The two eyes turn inward. Convergence and divergence reduces disparity to zero. Convergence is more used than accommodation. These cues are the only ones beside familiar size that can tell us the exact distance to an object. Chameleons for example use the absolute metrical depth cue from convergence to catch prey insects with their tongues. Divergence: as we shift focus from a close point to a far one. The two eyes turn outward. Corresponding retinal points: a geometric concept saying that points on the retina of each eye where the monocular retinal images of a single object are formed are the same distance from
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