Form Perception 2 - Form Perception 2 Module 1 Features Detectors Division of labour Each region processes specific information and passes it on

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Form Perception 2: Module 1: Features Detectors: Division of labour Each region processes specific information and passes it on Magno and Parvo cells transducer light stimulus into neural impulse Retina axons exit through optic nerve travel to LGN primary cortex on occipital lobe Cells in the visual cortex are very particular about what makes them fire: feature detectors 1952-Hodgkin/Huxley record electrical activity in a neuron of a squid 1959-Lettvin found neurons in frog that only responded to black moving dots “bug detectors” 1962-Hubel/Wiesel expanded Lettvin’s work in cats and monkeys Tried to learn what type of stimuli individual cortical cells respond to Put microelectrodes in cortex of a cat to measure neurons response to stimuli They weren’t getting any response from the neurons Presented a slide with a crack in it, neurons went wild Neurons must respond to specific stimuli Began using different lines of different thickness/orientation/movement Each neuron fires maximally to a specific stimuli, this defines the cell’s receptive field Simple cell: responds maximally to a bar of a certain length and orientation in a particular region of the retina Eg. Cell fires rapidly with stimulus, stimulus moved or changed in orientation, cell is inhibited and fires less than baseline; receptive field organized in opponent fashion making it sensitive to the location of the bar within the receptive field Complex cell: responds maximally to a bar of a certain length and orientation, regardless of where the bar is located within the receptive field Eg. Still fires even if moving, some neurons particular about that movement Hypercomplex cells: respond maximally to bars of a particular orientation that end at specific points within the receptive field Eg. Cell fires the most to any horizontal bar that appears anywhere in the on region, but gives a weak response if the off region is touched slightly The layout of the visual scene is preserved in the cortex; neighbouring objects in visual field are processed by neighbouring areas in the brain Is not exact because most cortex processing information from the central part of the visual
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This note was uploaded on 04/17/2009 for the course PSYCHOLOGY 1XX3 taught by Professor Kim during the Spring '09 term at McMaster University.

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Form Perception 2 - Form Perception 2 Module 1 Features Detectors Division of labour Each region processes specific information and passes it on

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