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Psychology Chapter 6.docx

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Steve Joordens

Psychology Chapter 6 PerceptionThe primary function of the sense organs is to provide information to guide behaviour In terms of vision or brain receives fragments of information from approximately 1 millionaxons in each of the optic nerves It combines and organizes these fragments into perceptions of a scene objects having different forms colours and textures residing at different locations in a three dimensional space Even when our bodies or our eyes move exposing the photoreceptors to entirely new pattern of information our perception of the scene does not change at all We see a stable world not a moving one because the brain keeps track of our own movements and those of our eyes and compensates for constantly changing patterns of neural firing that these movements cause PERCEPTION the process by which we recognize what is represented by the information provided by the sense organs This process gives unity and coherence to this inputIts a rapidautomatic unconscious processWe dont see an object and perceive it We simply perceive it If you look at a tall cylindrical object on a countertop you immediately perceive a glass and subsequently perceive the smudges near the topsthe lettering on its sideetc BRAIN MECHANISMS OF VISUAL PERCEPTIONVisual perception by the brain is described as a hierarchy of information processing According to this schemecircuits of neurons analyze particular aspects of visual information and send the results of their analysis to another circuit which performs further analysis At each step in the process more complex features are analyzed The process leads to perception of the scene and all objects in itPRIMARY VISUAL CORTEXDavid Hubel and Torsten Wiesel inserted microelectrodesextremely small wires with microscopically sharp points into various regions of the visual systems of cats and monkeys to detect the action potentials produced by individual neurons The signals picked up the microelectrodes electronically amplified and sent to a recording device for later analysis After positioning a microelectrode close to a neuron Hubel and Wisel presented various stimuli on a large screen in front of the openeyed but anaesthetized anima The anaesthesia makes the animal unconscious but does not prevent the neurons in the visual system from responding Hubel and Wiesel concluded that the geography of the visual field is retained in the primary visual cortex The surface of the retina is mapped on the surface of the primary visual cortex This map of the brain is distorted with the largest amount of area given to the centre of the visual field where our vision is most precise Module a block of cortical tissue that receives information from the same group of receptor cellsIt s 05 07 mm in size and contains approximately 150000 neurons all of the neurons within a module receive the same information from the same region in the retinaBecause each module in the primary visual cortex receives information from a small region of the retina this means it receives information from a small region of the visual field the scene that is currently projected onto the retina Hubel and Wiesel found that neural circuits within each module analyzed various characteristics of their own particular part of the visual field
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