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Module - Form Perception.doc

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Joe Kim

FormPerception TheGestaltPhilosophy -1920s, psychologists in germany studied how people perceive the world around them -gestalt psychs, believed that “the whole is diff. than the sum of its parts” -believed people perceived the whole stimulus instead of putting everything together -this movement was a reaction to the structuralist approach -ex: watching a movie (made by taking pictures every second). no continuous movement in the frames, but we still perceive movement as you watch the rapid sequencing of pics -motion is an emergent property of the seq. of pictures -psychs also proposed laws of organization: laws that describe how we organize visual input, thought they they are innate, and we acquire them rapidly SixGestaltPrinciples:Figure-ground -ability to determine what aspect of visual scene is part of the object itself and whats part of background -ex: vase of flowers against a flowery wallpaper -ex: simple scenario: small region that is surrounded by a larger region (background). figure would have edges so its perceived as its in front of the background -ex: white snowman against black background -usually do it so often and automatic that it seems easy. this can be hard if the cues that are used to make these discussions are not clear (such as reversible figures) -ex: pic that looks like a wine glass or two people about to kiss, depending on what you perceive to be the background SixGestaltPrinciples:Proximity -elements that are close together in space tend to belong together -field of daises, which aren’t all spaced apart but have regions where they are clustered in some numbers -you naturally see the regions of high daisy density as one group b/c they are close to each other and clustered, instead of grouping together daises from one cluster from another cluster -ex: row of X’s that vary in spacing. you will group together the x’s that are close together than the ones that are far SixGestaltPrinciples:Closure -if there are gaps in the shapes, we tend to fill in those gaps and perceive it as a whole object -ex: you will perceive it as a rectangle even though there are gaps in it. you have tendency to fill them in, eyes will automatically perceive the shape SixGestaltPrinciples:Similarity -tendency to group together elements that are physically similar -ex: farmers field, alternating rows of sunflowers and corn. even though distance between rows might be same, or less then the distance b/w plants, you tend to group the vegetation of the same type -ex: grid of alternating rows of X’s and O’s. you tend to see the columns of the same elements, and group them together. instead of growing together a row of x o x o SixGestaltPrinciples:Continuity -lets us perceive simple continuous form instead of a combination of awkward forms -ex: letter X is perceived as two continuous lines (/ and \) put together instead of the top and bottom halves -ex: vase of flowers. your gonna see a stem as a continuous line, even though it might be crossed with another stem. SixGestaltPrinciples:CommonFate -idea that things that change in the same way should be grouped together -ex: group elements together if they are moving in the same direction at the same time -ex: group of fish moving in same direction. tendency is to group them together as one kind of object -also explains how we see a camouflaged animal once if moves -ex: moth against a tree. when its still you cant its parts. but when it moves, the elements within the moth are moving together in the same direction/same time. these moving elements within common fate, allows the moths shape to be perceived Pattern/ObjectRecognition -ex: joe told me that he was excited to see an upcoming costume ball, and saw this picture. most ppl would perceive that its a costume ball scene. if he told me he wanted to go to marine land, you’d interpret the same pic in diff way. shows that people when people expect to see something, that can influence what they actually see -most important step is to figure out whats parts of the background and what aspect is the figure -once you know that, the parts of the figure are identified and grouped together into on object Bottom up processing -recognizing an object is two processes 1. bottom up: where features that are present in the stimulus guides object recognition ex: you recognize a cow because it has four legs, goes moo, udder, big nose, two long ears on side, two big eyes. -bottom up processing says you recognize what you see by analyzing the individual features and comparing them to things with similar features you have in your mind Top down processing -where your own beliefs are the primary influence for what your seeing ex: the second letters in both words are the same, but you read it as the cat because your influenced by the context ex: a b c d e f 10 11 12 13 14, letters that make up b and 13 are same, but you see them as diff. ex: priming: experimenter measures how fast someone can read the word that flashes on the screen. if you tell them the next word is an animal, you’ll find the priming effect cause words like dog/duck are recognized faster than log/puck. shows that processing a word is better if the person expects the word to be from a specific category -top down processing cant work alone cause you need input from the stimulus too before your expectations about that stimulus can influence your recognition of it -bottom up processing cant happen alone either cause our expectations will influence us too -both processes are involved, and its bi-directional activation (processing occurs in both directions at once) -so features of the objects are combined with expectations Biedermans Geon Theory -we have 36 geometrical forms, stored in our memory (forms like cone, sphere, cylinder) -using all these can recognize over 150 million objects -ex: ice cream is a cone and a sphere. garbage can is cylinders -some problems. cause certain stimuli, likes faces or crumples paper, and its difficult to determine which geon it is -evidence: some brain damage leads to specific deficits -ex: brain injuries may not be able to recognize some fruits, but can name different types of tools -if geons were involves, then there would be deficits in recognizing all objects and not a specific category of them (since its all based on the shape of it) Template Theory -store many different templates in our memory, and when see object, we compare it to the templates -if it matches, then its a familiar thing and person can name it by activating connections to other language areas in the brain. -if no match, its unfamiliar, and a new template is stored -dont like it cause we have to store so many templates to recognize all the objects Prototype theory -we store the most ideal example of an object -how we easily recognize common objects that we have not seen before, new dog -also recognize specific individual objects like our down -so its possible we have more than one type of rep. of each object, like one ideal dog and all the dogs we are familiar with Parallel Processing -we can recognize objects as fast, cause neural processing of object info is done in parallel -different brain systems processing diff. comp. of the visual signal simultaneously -ex: simultaneous processing of both form and color of object PerceptualConstancies -ability to perceive an object as unchanging even through the visual image produced by the object is constantly changing 1. Shape -we perceive objects to have a constant shape, even though actual retinal image of the shape would change as your pov changes or if object changes position ex: you perceive the shape to be rectangular, but it only produces a rectangular retinal image if your looking straight at the door. when you move, or door opens, the retinal shape isnt rectangular, but you still perceive it to have a constant rectangular shape 2. Location -objects are moving around on retina as we move our eyes/head/body -but we still perceive the objects around us to be stationary ex: driving car, everything moving fast on our retina, but still perceive objects to be still 3. Size -tend to see the size of objects around as unchanging even through objects vary in distance from us -the size of the retinal image that they produce can vary quite a bit -ex: friend walks away from you, you don’t think he’s shrinking as your retinal image gets smaller. you think he’s still same size even as they are getting farther away 4. Brightness -to know the brightness of objects around us doesn’t change even tho the objects may reflect more or less light depending on conditions ex: we see our fav mug as same brightness, even if we see it outside or in dark room -black still is black and white is white regardless of where we see it, even though the black object outside reflects more light than white object inside 5. Colour -way that we perceive objects around us to have a constant color even thought stimulus that reaches our retina may change depending on conditions ex: how u see your white dog to be white even if its under a red light and might look red Explaining constancies: Cues in Scene -depends on our existing knowledge about objects. -ex: we know our friend is constant size and mug is specific brightness, dogs a specific color, buildings dont move when we drive by them -our visual system has a way of picking up cues in the scene and use it for consistency in the object ex: use depth cues to know our friend is far away, that keeps us from seeing our friend shrinking in size as he moves further away. our retinal image is producing a smaller image, but you know from the cues that he’s just far away and still same size ex: driving car and you approach a bus, which stops in front of you. brain integrates the motion. if bus was moving towards you, everything in background would be stationary. when everything in scene comes closer to you, brain can use the info to say that your actually moving and that causes you to perceive the scene accordingly -perceptual constancy occurs cause certain object properties don’t change, and system factors in other cues in the environ. that give us info about that object VisualIllusions -happens when have ambiguous or partial info -Ex: dog with reddish cast in a scene with no other objects have reddish cast, we wont recognize the dog to be ours ex: which lines longer? actually same size. cause: misapplying size and depth -angled lines on top look like a corner, but ones on the left look like a corner that is pointed towards you, and right one looks like one away from you. since two lines give same retinal image, but one on left is closer to you, the closer one is thought to be shorter -ppl living in round huts and don’t have right angles, will know their the same lines. illusion is diff due to cultural/experience dependent processes ex: ames room, looks like rectangular but is actually a trapezoid. cause one corner is farther away from pov than other corner. so if two ppl standing in each corner, the person in farther corner looks smaller than the person standing closer to you. but since you think the room is rectangular, you think both ppl are same distance away from you. brain gets confused cause of the cues that are normally used for size constancy ex: pozno illusion: which line is longer? same length -this is cause, both lines are converging, which gives a sense of depth. you need to perceive the top of the lines where they converged the most, as being farther away than bottom of the lines, where they are further away -cause top line is perceived to be further away, you think its longer than bottom (and cause that looks closer to you) FeatureDetectors Magno and Parvo Cells -magno cells are found in periphery of retina, used for detecting changes in brightness (and motion and depth) -parvo cells are throughout retina, for detecting color change, pattern, form -these ganglion cells, have small receptive field and is first step of of object recognition -cells are called feature detectors -first they transduce light stimulus onto a neural impulse -from retina, their axons exit the eye via optic nerve, travel to lgn, end up in PVC in OL -1952, hodgkin and huxley recorded electrical activity in individual neuron of a squid, helped other researchers use this technology to see how neurons respond to stimuli -ex: 1959 lettvin discovered neuron in optic nerve of a frog that responds to moving black dot, and called them bug detectors -hubel and wiesel did studies of cells in visual cortex of monkeys and cats, won nobel p -in 1962: they explored visual cortex by trying to learn what type of stimuli the individual cortical cells responded to -they did this by putting microelectrodes in the cortex of a cat to record the electrical activity of individual neurons as cat was shown diff. types of stimuli -problem: weren’t getting much response from the neurons -then showed cat a slide with a crack in it, when that line was projected onto cats visual field, neuron was going crazy -they realized that neurons must respond to stimuli that are more complex -they started using lines of different orientation/thickness that moves in directions, and found each neuron is very
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