Chapter 3 notes
Chapter 3 notes Psyc4106W
Popular in Sensation and Perception
Popular in Psychlogy
This 5 page Class Notes was uploaded by Jennifer Gittleman on Wednesday October 28, 2015. The Class Notes belongs to Psyc4106W at George Washington University taught by Dr. Philbeck in Fall 2015. Since its upload, it has received 27 views. For similar materials see Sensation and Perception in Psychlogy at George Washington University.
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Date Created: 10/28/15
I Introduction a Neural processing interaction of the signals in many neurons ll Lateral Inhibition and Perception a Lateral Inhibition inhibition that is transmitted across the retina founded on the Limulus horseshoe crab b Lateral Inhibition in the Limulus i Hartline Wagner and Ratliff used the Limulus to show how lateral inhibition can affect the response of neurons in a circuit ii Limulus eye is made up of hundreds of tiny structures called ommatidia 1 Each ommatidia has a small lens on the eye s surface that is located directly over a single receptor 2 Each lens and receptor is large so you can illuminate a single receptor 3 When they added illumination to several receptors the ring rate decreased because of lateral inhibition c Lateral Inhibition and Lightness Perception i Perceptual phenomena that have been explained by lateral inhibition and involve the perception of lightness perception of shades ranging from white to gray to black 1 The Hermann Grid Seeing Spots at Intersections a Demonstration of how lateral inhibition can create the spots in the Hermann grid by affecting the ring rate of neurons in a neural circuit 2 Mach Band Seeing Borders More Sharply a Illusory light and dark bands near a lightdark border 3 Lateral Inhibition and Simultaneous Contrast a Simultaneous contrast occurs when our perception of the brightness or color of one area is affected by the presence of an adjacent or surrounding area d A Display That Can t Be Explained by Lateral Inhibition i White s illusion 1 Not caused by lateral inhibition but it s because our perception of lightness is in uenced by belongingness an area s appearance is in uenced by the part of the surroundings to which the area appears to belong III Processing from Retina to Visual Cortex and Beyond a Responding of Single Fibers in the Optical Nerve i Receptive eld retinal region over which a cell in the visual system can be in uenced excited or inhibited by light vi vii viii Fiber s receptive eld covers hundreds or thousands of receptors which means the ber is receiving converging signals from all of the receptors Receptive elds of different bers may overlap which means shining light on a point of the retina activates many ganglion cell bers Centersurround organization in cat receptive elds the area in the center of the receptive eld responds differently to light than the area in the surround of the receptive eld Excitatory area presenting a spot of light to the center increases ring in the receptive eld Inhibitory area stimulation of the surround causes a decrease in ring in the receptive eld Excitatorycenter inhibitorysurround receptive eld receptive eld which responds with excitation when the center is stimulated and inhibition when the surround is stimulated Inhibitorycenter excitatorysurround receptive eld receptive eld which responds with inhibition when the center is stimulated and excitation when the surround is stimulated Centersurround receptive elds showed that neural processing could result in neurons that respond best to speci c patterns of illumination which was proved by centersurround antagonism Centersurround antagonism small spot of light presented to the excitatory center of the receptive eld causes a small increase in the rate of nerve ring and increases the light s size so it covers all of the receptive eld and increases the cell s response used when the spot of light starts to become bigger and cover the inhibitory area stimulation of inhibitory surround causes a decrease in the neuron s ring rate neuron responds best when the spot of light only hits the excitatory center b Hubel and Wiesel s Rationale for Studying Receptive Fields Neurons at higher levels of the visual system become tuned to respond best to more and more speci c kinds of stimuli Instead of shining light directly into the eye they had animals look at a screen on which they projected stimuli LGN regulates neural information as it ows from the retina to the cortex receives more signals from the cortex than from the retina feedback information the LGN receives back from the brain plays a role in determining which information is sent to the brain iv Cerebral cortex covering of the brain that plays a role in determining perception and cognition v Occipital lobe visual receiving area place where signals from the retina and LGN rst reach the cortex vi Superior colliculus receives some signals from the eye plays a role in controlling movements of the eye vii Striate cortex another name for visual receiving area has a striped appearance area V1 indicating that it is the rst visual area in the cortex c Receptive Fields of Neurons in the Visual Cortex i Simple cortex cells cells with sidebyside receptive elds not centersurround respond to small spots of light or stationary stimuli ii Orientation tuning curve relationship between orientation and ring determined by measuring the responses of a simple cortical cell to bars with different orientations iii Complex cells respond only when a correctly oriented bar of light moves across the entire receptive eld respond best to a particular direction of movement their receptive elds aren t indicated by pluses or minuses but by outlining the area that brings out a response iv Endstopped cells re to moving lines of a speci c length or to moving cornersangles v Feature detectors simple complex and endstopped cells re in response to speci c features of the stimulus orientation direction of movement IV Do Feature Detectors Play a Role in Perception a Selective Adaptation shortterm effect i We view a stimulus with a speci c property which causes certain neurons to re the ring causes neurons to eventually become fatiguedadapt ii The adaptation causes the neurons ring rate to decrease and the neuron res less when that stimulus is immediately presented again iii Contrast threshold minimum intensity difference between two adjacent bars that can just be detected iv Selective adaptation experiment measures how a physiological effect adapting the feature detectors that respond to a speci c orientation causes a perceptual result decrease in sensitivity to that orientation b Selective Rearing longterm effect i If an animal is reared in an environment that contains only certain types of stimuli then neurons that respond to these stimuli will become more prevalent ex rearing an animal in an environment that contains only vertical lines should result in it s visual system having neurons that mostly respond to verticals ii Neural plasticityexperiencedependent plasticity the response properties of neurons can be shaped by perceptual experience iii Example kittens placed in tube use it or lose it c HigherLevel Neurons i Inferotemporal IT cortex Charles Gross decided this area in temporal lobe should be studied because it affects how you recognize objects and is related to prosopagnosia people with temporal lobe damage are unable to recognize faces ii He recorded from single neurons in monkey s IT presented different stimuli lines squares circles light stimuli dark stimuli iii Found that some neurons respond best to hands and faces iv Fusiform face area area on temporal lobe that responds strongly to faces V The Sensory Code a Sensory coding how the ring of neurons represents various characteristics of the environment b Speci city Coding Representation by the Firing of a Specialized Neuron i Speci city coding a particular object is represented by the ring of a neuron that responds only to that object and to no other objects there are neurons that are speci cally tuned to each object in the environment ii Grandmother cell a neuron that responds only to stimulus regarding grandmothers picture of your grandmother idea of your grandmother c Distributed Coding Representation by the Firing of Large Groups of Neurons i Distributed coding the representation of a particular object by the pattern of ring of a large number of neurons a large number of stimuli can be represented because groups of neurons can create a lot of different patterns d Sparse Coding Representation by the Firing of a Small Number of Neurons i Sparse coding occurs when a particular object is represented by a pattern of ring of only a small group of neurons the particular neuron can respond to more than one stimulus VI The MindBody Problem a Mindbody problem how do physical processes become transformed into perceptual experiences b Neural correlate of consciousness NCC relationship between the ring of neurons and stimuli in the environment c Easy vs hard problem of consciousness easy is looking for connections between physiological responding and experiences hard is determining how physiological processes cause us to have experiences
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