Form Perception I PDF

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Form Perception I Tuesday, January 7, 2020

12:39 PM

UNIT 1: Intro to Form Perception • Distinguishing figure from background is a complex visual function UNIT 2: Gestalt Principles • The Gestalt psychologists firmly believed that “the whole is different that the sum its parts” • Believed that people tend to perceive the whole stimulus rather than each indiv a reaction to the structuralist approach; suggested that everything could be redu to basic elements • Motion is an emergent property of a sequence of pictures; the perception of the movie in its entirety is something more than the collection of thousands of still photographs ○ Analyzing every photograph would never provide you the same rich exper that you would get from watching the movie Gestalt Principles: Laws that describe how we organize visual input • They believed that we are either born with these laws of organization or groupin tendencies which are called the Gestalt principles or that we acquire them very rapidly 1. Figure-Ground The ability to determine what aspect of a visual scene is part of the object itself and w is the background • Figures tend to have distinct borders that give it form over the background ie. snowman example • Are constantly determining what is figure and what is background often automat but is more difficult if the cues used to make these figure-ground decisions aren clear ie. with reversible figures 2. Proximity The tendency to group elements that are close together in space • Naturally see regions of high density as one group due to proximity • More likely to group objects closer together than far apart 3. Closure Tendency to fill in gaps in a contour to perceive a whole object • Automatically fill in parts we can’t see to perceive a single object • We can perceive a rectangle despite obvious gaps 4. Similarity Tendency to group together elements that are physically similar

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• Tend to group together objects of the same type • Tend to see columns of the same elements as belonging together 5. Continuity Ability to perceive a simple, continuous form rather than a combo of awkward forms • Tend to perceive an X and 2 continuous lines rather than 2 V’s • Tend to perceive each stem as a single continuous line even if they’re criss-cros with other stems 6. Common Fate Tendency to group together elements that change in the same way • Objects moving together in the same direction/at the same time tend to be group together; make us think that the group of objects is one • Elements within a moth’s movement reveals it from the background; why we can suddenly see a camouflaged animal once it moves UNIT 3: Pattern/Object Recognition • Expectation shapes what we see • First step in object recognition involves identifying what aspect of the scene is th figure and what is the background • One established, the parts of the figure are identified and grouped together into single object Bottom-Up Processing: Object recognition is guided by the features that are presen the stimulus • Recognize a cow by comparing every feature to memory Top-Down Processing: Object recognition is guided by your own beliefs and expectations; primary influence for determining what you’re seeing • Recognize “THE CAT” even if the second letter in both words are physically identically; you are influenced by the context • Also seen in priming ○ Priming experiment has experimenter measuring how fast a participant ca read a word that is flashed on the screen; if you tell the participant the nex word is an animal, you find a priming effect b/c words like dog or cat will be recognized a lot faster that log or mat ○ Shows that processing of a word is more efficient if the participant is prime expect a word from a certain category • This processing requires some input from the stimulus to work before your expectations about stim can influence your recognition of it • Bottom-up can’t explain everything alone either b/c we do rely on our expectatio • Bottom-up and top-down processing guide object recognition • Both of these processes must be involved and that we’re dealing with bi-directio activation where processing occurs in both directions at once; this way the featu

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• Both of these processes must be involved and that we’re dealing with bidirectional activation where processing occurs in both directions at once; this way the features of the object in combination with our expectations guides object recognition • Object recognition can rely on varying degrees of processing • Geon theory suggests that we have 36 different geons (simple geometrical forms) stored in memory and with just the 36, it is possible to recognize over 150 million diff objects Ie. ice cream cone is just a cone and a sphere • Problem is that its difficult to imagine the geons used in more complicated objects like faces or crumpled pieces of paper but we have no difficulty recognizing these stimuli • Evidence that some forms of brain damage lead to very specific deficits may not be able to recognize diff types of fruit but can name diff types of tools; if geons were involved, may expect deficits in recognizing all types of objects based on their shape and not specific category ○ Also possible that geons could be processed at a diff level of processing separate from the area of brain damage • Template theory suggests that we compare objects to templates in memory ○ When we come across an object we compare that object to all the templates in memory; if a match is found then its familiar object and the person could name it by activating connections to other language areas in the brain ○ If no match is found, a new template is stored in memory • Problem is that we would have to store a very large amount of diff templates you’d need to recog all the diff objects we encounter • Prototype theory suggests that we compare objects to our most ideal/typical prototype; this overcomes the storage problems of template theory • Much more flexible because doesn’t require an exact match; this is how we can easily recog common novel objects • Able to process objects quickly and efficiently b/c much of the neural processing of object info is done is parallel ○ Diff brain systems process diff components of the visual signal simultaneously UNIT 4: Perceptual Constancies • We retain perceptual constancy despite variation in visual stim Perceptual Constancy: Our ability to perceive an object as unchanging even though the visual image produced by the object is constantly changing 1. Shape Constancy

Object is perceived to have a constant shape despite the shaped of its retinal image changing with shifts in POV or object position • A door is perceived as rectangular despite its visual change when opening 2. Location Constancy An object is perceived to be stationary despite changing location on our retina due to body movements • While driving, we don’t perceive the objects outside to be moving 3. Size Constancy Object is perceived to be the same size despite the size of its retinal image varying with distance • A friend walking away is not perceived as shrinking in size; he is just getting farther away from you 4. Brightness Constancy Object is perceived to be the same brightness despite reflecting more or less light onto our retina • Objects have the same brightness whether in high or low illumination; black still looks black and white still looks white • Context can make things look diff 5. Colour Constancy Object is perceived to have a constant colour despite diff illumination conditions • A white dog is still recognized even under a reddish light (so long as a range of other colours are available in the background for reference) • Existing knowledge provides top-down influence on perception • Existing knowledge makes sense of changing visual stimuli; buildings don’t move as we drive by them • Cues in scene indicate perceptual constancies Ie. use depth cues to both determine our friend is far away and shape how we perceive our friend in that context ○ Use depth cues to keep us from seeing our friend as shrinking in size as her moves further away • Colour cues indicate influence of light on an objects colour • Our brain integrates the motion of all the elements in a scene • Perceptual constancies exist from prior knowledge and cues in our scene; we know that certain object properties don’t change and our perceptual sys automatically factors in other cues in the environ that give us info about the object of interest...