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UO PSY 201 - 3-D Form and Depth Perception

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PSY 201 1st Edition Lecture 9Outline of Last Lecture I. Three perceptual dimensions of colorII. Color and wavelengthIII. Color mixing: additive and subtractiveIV. Two theories of color visiona. Trichromatic theoryb. Opponent process theoryV. PsychophysicsVI. Perceptual OrganizationOutline of Current LectureI. 3-D form and depth perceptiona. perceptual constanciesII. Bottom-up and top-down processingCurrent LectureI. 3-D form and deptha. Binocular cues: require two eyes, and works for objects less than approximately 30 feet awayi. retinal disparity: two eyes are in different positions, and therefore get different views of the worldb. Monocular cues: can be used with one eyei. Motion parallax: how parts of the world move in relation to each other gives information about depthii. Pictorial cues: shape from contour; shading. Lighting, linear perspective, texture, elevation, etc.c. Retinal/binocular disparity: since the eyes are in different positions, they receive different views of the worldi. The brain interprets the differences between the two images as depthii. Stereoscope: a device through which two pictures are taken and viewed by each eyed. Motion parallax: one of the most important cues for depth perception, in which motion of elements gives an impression of depthi. When you move your head, objects at different distances move at different speedsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Optic flow: when you move toward or away from objects you focus on movement differently1. Swinging room: moving the room forward creates the illusion that you’re moving backward, and so you automatically correct your position2. Structure from motion: a person got lights on elbows, knees and joints, put into a dark room and were filmed. When the person begins to move, only then is structure observablee. Pictorial cuesi. Shape from contour: the way contours interest to provide depth1. T junction: a T suggests occlusion or interposition2. Cross: suggests two wires lying over each other3. For: suggests corner shape4. Each intersection puts constraints on organization5. ‘Impossible figures’: optical illusionsii. Shading and lighting1. Surfaces facing light source are brightest2. Interpret pattern of shading as shape; we usually assume that the light source is coming from aboveiii. Linear perspective/texture gradients1. Decrease in size and spacing of distant elements2. Linear perspective: apparent convergence at a distance of parallel linesa. Texture gradients: refinement of size and spacingi. Objects that are closer look larger and are more spaced out iv. Relative image size: two objects of the same shape but they will be judged differently according to depth levels (something smaller looks far away)v. Elevation: proximity of an object to the horizon line (closer to horizon= larger)vi. Aerial and atmospheric perspectiveII. Perceptual constanciesa. Humans are good at extracting common properties in the worldi. Lightness constancy: apparent lightness of an objectb. Shape constancy: perceived shape of an object is the same regardless of viewing anglei. Sort of the like the idea that people don’t shrink when they’re further awayc. Size constancy: a perceived object’s size is the same regardless of the distancei. When you estimate size, you take retinal image size and perceived distance into account (both of these things are needed to estimate actual physical size)ii. Sp (perceived size)=Sr (retinal image size) xDp (perceived distance)1. Illusions: Ames room, moon illusion, Muller-Lyer illusion and ponzo illusiona. Ames room: works because the room is perceived as having a parallel back wall but the back wall is actually trapezoidali. The ‘smaller’ person’s distance from the peephole is actually father than what is perceivedb. Moon illusion: moon looks larger at horizon that zenithi. Horizon is perceived as further away because of depth cuesii. Sky is perceived as flattened domec. Muller-Lyer and Ponzoi. Two lines shown; the line that looks longer is seen that way because it seems ‘further away’ii. Perspective cues lead someone to make assumptions about distanceIII. Bottom-up and top-down processinga. Bottom up processes: sensory processing that begins with a local stimulus and brings them together to form the whole imagei. Starts with simple images and then goes to complexb. Top down processes: makes use of knowledge to perceive the worldi. Perceptual set: what we see is influenced by our expectations of what we will be perceivingii. Context effects: use of knowledge from the past to help perceive inputc. Biederman experiment: a dot is flashed on a blank screen, and then an image on the dot (people would identify the object)i. Images in proper context helps people match the correct


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