Lecture 4 notes
Lecture 4 notes Psyc4106W
Popular in Sensation and Perception
Popular in Psychlogy
This 4 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 20 views. For similar materials see Sensation and Perception in Psychlogy at George Washington University.
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Date Created: 10/28/15
Selective Adaptation Experiment 0 Feature detectors ex orientation of line segments 0 Show people a high contrast of bars 0 If you stare at high contrast vertical bars you won t be able to see the vertical bars as well but doesn t affect how you see horizontal bars 0 You sit someone in front of computer do contrast threshold like we did in lab but you do it for vertical off vertical horizontal all diff orientations then you do selective adaptation adapt people to bars of one orientation aka vertical and retest contrast threshold some adaptation makes it harder to see bars and other bars it doesn t affect it ability to see bars is most affected when the bars are most similar to the bars you adapted to if you adapt to high contrast vertical bars that s the hardest to see when it s dim doesn t affect ability to see horizontal bars 0 Similar to working a set of muscles Spatial frequency 0 Has to do with how close together the lines are if the lines are widely spaced low if the lines are closely spaced high 0 Can measure frequency by how many bars are in one image 0 Sine waves smooth transition from light to dark and follows sine wave function 0 Unit cyclesdegree how many cycles are packed into one degree 0 30 cycles in one degree 0 Have to have the spatial frequency match to the orientation 0 Simple cells are orientation and spatial frequency detectors Spatial Frequency tuned cells 0 Neuron ring rate not a person sitting in front of a computer What is contrast sensitivity function plot out axes what experiment to test CSF lowhigh sf how we adapt at a certain frequency Show them very high contrast set of bars at the adapting frequency have them stare at it for several minutes have them do an adjustment so they can barely see dim bars Fourier synthesis 0 You can add together spatial frequencies to capture things that have sharp edges Ocular dominance columns cells tend to respond best when light comes into either left or right eye Direct imaging which part of brain are active Contrast sensitivity function cells tuned to spatial frequencies and will respond best to certain types high sensitivity means you can see them well so you only need a little bit of contrast Contrast threshold experiment present someone bars with a certain orientation and how much contrast until you can t tell there are bars Contrast sensitivity function what kind of experiment to get it how to do selective adaptation version of it shows evidence of spatial frequency channels label axis show the general shape quotlowquot quotmedium quot high 3 channels put all three together you get a normal visual outcome Speci city coding 0 Have one neuron that whenever it sees bill the neuron goes crazy when it sees bill onetoone mapping 0 For every object that we recognize we would have one neuron that responds to that one object not realistic Distributed coding 0 Three neurons that can encode many people 0 Reusing the neurons so they re ring at different degrees 0 More efficient and more robust to brain injury Double dissociation paradigm 0 Sound and picture don t have anything to do with each other or sound and picture work together 0 Which of these two organization systems do we have inside the TV 0 You can get two TV sets one that has only sound working and only has picture working and can tell how independent they are o If the sound works and there is no picture evidence the two things are independent o If you have double dissociation that s giving you important info on how independent the two mechanisms are in the brain 0 Single disassociation someone is able to perceive where something is but doesn t know what it is 0 Double disassociation in two individuals and you see one person can see where something is but doesn t know what it is and vice versa opposite symptoms Two chains of neurons from primary visual cortex 0 Posterior parietal cortex important for controlling actions telling where things are 0 lnferotemporal cortex identifying what the objects are 0 Retinotopic organization 0 Two cells that are close to each other in the brain will have receptive elds that are close to each other Cortical magni cation 0 Small part of visual eld gets a lot of the representation of visual cortex Orientation columns o If you drop electrode straight down and record from cells you get and map out their receptive elds will have the same orientation preference Ocular dominance 0 Each cell in visual cortex has a preference of light coming from one eye or the other those cells tend to be grouped together LGN vs visual cortex 0 What s the organization in both 0 Cortex orientation preference 0 LGN receptive eld shape centersurround shapes those cells don t have orientation preference because they re circles need to get orientation right to re cells at their maximum 0 Optical imaging 0 Expose part of skull and put illuminator on part of cortex 0 Put bars of light in any orientation ocular dominance and orientation tuned cells on monitor in front of monkey 0 Data display is what the data you get not the stimulus 3 pics 0 Left pic when part of brain is active more blood has to be pumped there to sustain that activity you can measure and see that as an increased retinas of the cortex in parts of brain that are most active you can compare image of brain when looking at something from left eye or right eye 0 Middle pic the diff gradations are telling you what the organization in ocular dominance columns is 0 Right pic all areas that are red have the same orientation preference color is the same they have same orientation preference 0 Showing isoorientation contours black lines separate diff eyes Ungerleider and Mishkin 0 Each monkey learned how to do each test object discrimination and landmark discrimination Object monkeys had to learn the familiar object and look under it and got a reward for it ability to assess visual appearance Landmark wherever cylinder is that s where the food is and the monkeys are trained to go to that cylinder for food be able to discriminate locations In one group they created a brain injury in parietal lobe and other group created injury in temporal lobe test them again w injuries Object with lesion parietal was okay temporal was impaired Landmark with lesion parietal was impaired temporal was okay Double dissociation was found these functions seem to be processed in separate parts of brain dorsal stream specialized for using vision to localize objects where stream ventral stream specialized for using vision to identify what the object was what stream 0 Milner and Goodale OO DF human patient took shower and the hot water heater was in the bathroom and there was a carbon monoxide leak deprives your brain of oxygen and caused brain damage parts of ventral stream got damaged got visual form agnosia if you show them a pile of keys they wouldn t know what it is they know what keys are but can t use vision to recognize objects messes up ventral stream Ventral stream is used for identifying objects but the function of the dorsal stream is not purely location but how you use vision to tell your body how to act on locations in space it s not where it s how Optic ataxia patients that have damage in posterior parietal in dorsal stream messes up dorsal stream Diff parts of brain when you perceive places and faces Both are represented in ventral stream but different regions Parahippocampal Gyrus gets activated when people are viewing places Show faces or objects or lego objects not a huge amount of change but the more you arrange legos so they look like a place you see more activation in this area and if you show rooms that will active the area FFA if you show faces that s where it will be activated