Perception & Action - The Visual System Optics...

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The Visual System Optics o System to control light and focus it on a sensitive surface o Pinhole camera Small hole focuses light in correct location But small hole = not much light! o Iris allows more or less light Adjustable lens focuses light But depth of field problem Big hole = shallow area of focus But we rarely experience the depth of field of our own eye! The Retina o Rods Luminance detection o Cones Color vision 3 types of cones Red Blue Green Luminance detection for a particular wavelength o Fovea Center of retina 1
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Cluster of cones o Parafovea Rest of retina More rods than cones At night, better vision or of the corner of your eye Lateral Geniculate Nucleus (LGN) o Center Surround Cells Luminance detection cells Color-opponent cells o Magnocellular Neurons Low Spatial Resolution Cover big visual field Fast Cell Response Turn on fast, shut off fast Color-insensitive o Parvocellular Neurons High Spatial Resolution Slow Cell Response Color-sensitive Primary Visual Cortex (Striate) (V1) o Lots of layers Extrastriate Cortex (V2) 2
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o Kanizsa Triangle V2 responds to illusory contours V1 responds to contours “What” and “Where” Systems o Dorsal Pathway Ventral Pathway Magnocellular/Dorsal/Where/How path Good for detecting motion Bad for detecting particular objects Parvocellular/Ventral/What path Good for recognizing particular objects Bad for detecting motion o “Vision” isn’t a unitary process! Vision isn’t a veridical process o We “mark sense” of the world o We don’t just store a veridical representation of the world Object Recognition The “what” path o Goal is to recognize objects o What they are Not where they are Not how fast they are moving 3
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Properties of the system o Robust to variability Can deal with noise in the system o Robust to “lossy” information Obscured o Properties of the underlying visual system There are detectors for “features” of various levels Activation of a point on the retina Lines are made up of rows of points Lines at different orientations o A theory of object recognition o “Synthesis by features” We recognize object by recognizing features of the objects And combining these into larger and larger units In the case of words, we recognize features that make letters that then make 
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This note was uploaded on 09/14/2008 for the course COGST 1101 taught by Professor Spivey,m during the Summer '07 term at Cornell University (Engineering School).

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Perception & Action - The Visual System Optics...

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