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Perception and Pattern Recognition

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University of Toronto St. George
Gillian Rowe

Perception and Pattern Recognition Today we will be looking at information surrounding the following question: "How does the process of perception depend on incoming stimulation and knowledge?" First, remember the difference between perception and sensation. Sensation is what the senses do and perception is the process of recognizing, organizing and interpreting information. Parsing Human beings posses something called perceptual intelligence, which is the knowledge of perception (such as previous experiences) and the knowledge we bring to a situation (i.e., when you wake up to your alarm clock and hit the snooze button, knowing you can still sleep for 10 minutes and make it to class). The central problem to perception is the question of how we attach meaning to raw material we receive from the environment. The primary goal of perception is to figure out what is out there and where it is. How do is the "what" and "where" processed in the brain? The "where" pathway: spatial properties. Goes from occipital lobe to parietal lobe. The "what" pathway: object properties. Goes from occipital lobe to temporal lobe. How do we perceive with our eyes? The retina receives an image of a stimulus. This activates the receptor cells in the retina (called rods and cones) that convert light energy into neural impulses. This information is meaningfully interpreted (it becomes the precept). Precepts are not the same thing as the information as it is out there and perception itself involves something more than the formation of images on our retina (size constancy). Bottom-Up Processing versus Top-Down Processing (1) Bottom-Up happens through the stimulation of receptors. If these receptors are not stimulated nothing will be perceived. Template, Prototype and Structural theories of perception fit into this type of processing. (2) Top-Down Processing is when we bring in our knowledge to identify and recognize stimuli. These two processes usually collaborate in order to create perception. Basically, incoming data from the environment can be affected by our knowledge, whether that knowledge be new, old or just realized. What is the rat man demonstration? There is a rat image and a mouse image in one. At first it may look like a rat or a mouse but as soon as someone mentions the other possibility, you begin to see both options. This shows that recently acquired knowledge can influence perception and that knowledge of context provided by a scene can influence perception (consider Stephen Palmers experiment). What is Template Matching? This is how early cognitive psychologists studied perception. It eventually lead to the idea of perception as based on features. Basically, the concept is that when a perception fits a template, you recognize it as such (template for triangle, box, cat, etc). This works well with simple situations (like cheques). The problem however is that there are too many objects out there in order to have a template for all. So, from there developed the theory of perception based on features. What is the Interactive Activation Model/Prototype Matching? This model purports that there are feature detectors that respond to oriented lines. This idea led to one that said that perception is constructed from simple features of and from the environment. Which ultimately solved the problem with template matching (requiring too many templates). But, although this theory allows for more flexibility than template matching it is not a complete theory. It does not explain how prototypes are formed or how the best match is identified and selected and is not flexible enough (since there still needs to be a prototype for each pattern).Posner and Keele did a study in 1968 that required participants to classify images presented. The images presented were shapes made of dots. Each shape had a series of shapes that belonged in the same category but that were distorted. Participants were not shown the prototype (the original shape) and were asked to categorize the distorted shapes they saw. The results concluded that people are naturally good at creating prototypes and almost always got the distorted shape classified correctly. The prototype theories got their influence from Lombroso's idea that there is a prototypical face of crime. This lead to experiments on face prototypes. Where researchers mixed a set amount of faces together (4-10-20-34) and then measured how many times each face was measured more attractive. They found that the more mixed the face was (made more average) the more attractive it was said to be. The Model of Letter Recognition Created by McClelland and Donald Rumelhart. They proposed that activation of letters is sent through three levels: (1)Feature level: possesses feature units like straight and curved lines (2) Letter level: has letter units like letters of the alphabet (3) Word level: has word unites like y
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