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Chapter 5

PS262 - Chapter 5

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Elizabeth Olds

PS262 Chapter 5: Perceiving Objects and Scenes  The fact that a particular image on the retina can be created by many different objects is called inverse projection problem  People are able to recognize objects that are not in sharp focus; despite the degraded nature of these images, people can often identify most of them whereas computers perform poorly on this task  Another problem facing any perception machine is that objects are often viewed from different angles therefore always changing depending on which angle they are viewed from  The ability to recognize an object seen from different view points is called viewpoint invariance  Gestalt psychologists – means a whole configuration that cannot be described merely as the sum of its parts The Gestalt Approach to Object Perception  The idea that perception is the result of “adding up” sensations was disputed and then the G psychologists instead presented the idea the whole differs from the sum of its parts  When two stimuli that are in slightly different positions are flashed one after another wit the correct timing, movement is perceived between the two stimuli (this illusion is called apparent movement) because there is actually no movement in the display, just two stationary stimuli flashing on and off  When you make the contours vanish by placing your finger over the black circles you show that the contour was illusory and that our perception of one of the display is affected by the presence of another part  The structuralists would have a hard time explaining illusory contours because there is no actual contour so there cant be any sensations where the contour is perceived The Gestalt Laws of Perceptual Organization  Perceptual organization involves the grouping of elements in an image to create larger objects  Six laws of organization to explain how perceptual grouping such as this occurs: o The law of pragnanz (good figure) (or law of simplicity) is the central law of Gestalt psychology: every stimulus pattern is seen in such a way that the resulting structure is as simple as possible  Law of similarity causes circles of the same colour to be group together. Grouping also occurs for auditory stimuli. For example: notes that have similar pitches and that follow each other closely in time can become perceptually grouped to form a melody o The law of good continuation: points that when connected result in straight or smoothly curving lines that are seen as belonging together and the lines tend to be seen in such a way as to follow the smoothest path o The law of proximity or nearness: things that are near each other appear to be grouped together o 3 principles: the principle of common region: elements that are within the same region of space appear to be grouped together  The principle of uniform connectedness: a connected region of visual properties such as lightness, colour, texture or motion is perceived as a single unit  The principle of synchrony: states that visual events that occur at the same time are perceived as belonging together o The law of common fate states: things that are moving in the same direction appear to be grouped together  Example – when you see 100’s of birds flying together you tend to see the flock as a unit  Common fate is like synchrony in that both principles are dynamic…expect synchrony can occur with out movement and the elements don’t have to change in the same direction as they do in common fate o The law of familiarity: things that form patterns that are familiar or meaningful are likely to become grouped together  Example – the faces picture in the scenery Perceptual Segregation: How Objects are separated From the Background  Perceptual segregation is the perceptual separation of one object from another  The problem of what causes perceptual segregation is often referred to as the figure-ground segregation  When we see separate object, it is usually seen as a figure that stands out from its background which is called the ground o for example – you would probably see a book or papers on your desk as figure and the surface of your desk as ground  the contour separating the figure from the ground appears to belong to the figure; this property of the figure which is called border ownership means that although the figure and ground share a contour the border is associated with the figure  What factors determine whether an area is perceived as figure or ground? Shauna vercera used a phenomenological method to show that regions in the lower part of a display are more likely to be perceived as figure than regions in the upper part The Gestalt Laws as Heuristics  The reason for rejecting the terms “laws” is that the rules of perceptual organization and segregation proposed by the Gestalt psychologists don’t make strong enough predictions to qualify as laws  Heuristics – rules of thumb that provide a best-guess solution to a problem  We can understand what heuristics are by comparing them to another way of solving a problem called algorithms  An algorithm is a procedure that is guaranteed to solve a problem o Example – we learn for addition, subtraction and long division…if we apply these procedures correctly we get a right answer everytime  Heuristic may not h
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