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Chapters 5- 8 Notes

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University of Illinois
PSYC 204

Chapter 5: Perception and Encoding 2/18/2013 1:01:00 PM Primary Visual Cortex  Located in the occipital lobe, they are preserving a map of visual space. The map of visual space is inverted (upside down, and reversed)  Fovea- central part of vision, comes from the retina. Sending information to the most posterior part of the occipital lobe. o Central part of division gets many more neurons compared to information from the periphery (like primary motor cortex), or cortical magnification  There are 6 layers of neurons o All LGN ends up in layer four, where all the synapses are. Separate for each eye and each system. o P-Pathway- details and colors. Blobs- neurons in V1 that get input and are related to color vision. o Other cortical structures called pinwheels- related to orientation of edges Area V1 or Striate Cortex  Eye Dominance Columns o Pinwheels are responding to bars of light with sensitivity to different angles. It resembles a pinwheel. Area V2 or Area 18  Extra-Striate Cortex- regions that are surrounding the primary visual cortex o They also have a preserved spatial layout, neurons that are creating a map of visual space. o No longer have columns that differentiate the eye. Respond to edges moving in a particular direction, more complex than V1. Map of Cortical Areas  Multiple visual areas, V1, V2, V3, and V4  What kind of stimulus is best to getting a response in a certain region? “optimal stimulus” V4 and V5 Areas  V4: Color pathways  Optimal stimuli: only sensitive to moving object, receptive fields are very big, M-pathway February 20, 2013 Neurophysiological Evidence of Concurrent Processing  Different cortical areas are activated by different stimulus dimensions Visual Illusions  Why do we see something that is not actually there? What’s been found is that when someone is perceiving motion, Area MT/V5 is active even though nothing in the visual environment is moving. The same goes for color in Area V4. (Optical Illusions) It is artificial activation in Area MT that are coding for motion.  Even though there is no red light present, a spike of activity leads to the perception of red because of staring at the green.  Having to put together two separate features, get information from both cortical processes. If you have distractions, it takes longer because you are doing the search differently (you have to actively look and direct your attention to each location and space to confirm the conjunction between the two features). In order to do this search (putting together two different kinds of features) requires direct attention to a location in space. It allows you to bind together these features, and that’s because they are co-localized. Serial Search  Direct your attention one by one in order to find the target. We perceive things as being unified even though different areas of the brain process them as differently.  Feature Analysis- effortless processing  Feature Integration- slower, more effortful processing in order to glue together the outputs of what is being processed. Effects of Lesions  Daltonism o Deficit in opsin (cones), usually red- green colorblindness.  Achromatopsia o Acquired as a result of stroke (cortical damage or loss of all cones to area V4)  Loss of ability to distinguish all color  You can have deficits that are selective to specific parts of the visual field, this is due to the retina topic map in V4  Akinetopsia o Cannot see movement, like when something is moving and how fast it is moving. (Cars would appear out of nowhere). No ability to see if object moves from Point A to Point B. Described like a strobe light, or seeing the world in separate frames.  Hemianopia o Lesions of Area 17, cortical blindness, nothing is wrong with your eyes but you have lost the ability to see because you have cut out Area V1 o You can also lose one half of visual space if there is a lesion in only one half of the hemisphere (Remember video where he can’t see the finger wiggle) Cortical vs. Subcortical Pathways  Orienting your attention to a particular location in space- retino- collicular pathway.  Blind sight- you still have visual information coming in even though you technically cannot see it. People can make a motor response based on something in the visual environment even though they cannot visually see it.  Slower to respond to something in their preserved visual field if it is simultaneously presented in their blind field, rather than just being presented in their preserved visual field. Blind sight- Preserved Subcortical Pathway  Sensory apparatus hooked up to a motor apparatus. Visual awareness is separate and is doing something else other than guiding movement of our eyes in space.  Eyes will move to periphery area before you are even aware.  People are slower compared to when there was just one target in their good visual field. People are somehow aware that there is a stimulus in the blind field of vision. Animal Lesion Study  Localization vs. Discrimination Task o Animals have trouble orienting space in the localization task o You get a double dissociation. Animals do fine with visual discrimination because they have an intact visual cortex. Superior colliculus is used. Visual System Summary  “Divide and Conquer” strategy Ear and Hearing 2/18/2013 1:01:00 PM Auditory System Overview  Cochlea leads to the auditory cortex in the temporal lobe  Cochlea contains the basilar membrane surrounded by fluid o Has hair cells that interact with the tectoral membrane. It is sensitive to different frequencies, thinner end is for higher frequency sounds o Vibration of hair cells trigger action potentials, determine frequency on where the membrane is vibrating o Frequency and amplitude is encoded Range of Sound  20 and 20,000 hz  1,000 and 4,000 hz is where speech falls  recognizing auditory patterns that is related to speech Basic Features  Fast o Speech signals happen very quickly o Latency potentials= latency of 1- 5 ms o Much slower in the visual system to receive a potential  Tonotopic representation Auditory Stimuli  Audition= sense of hearing  Sound waves are characterized by: o Frequency (pitch) o Timbre (pattern or quality) o Amplitude (volume)  Sounds vary over time (speech) Hearing Problems with Aging  Presbycusis o Very common, decline in the ability to hear high pitched sounds o Degeneration in the cochlea  Tinnitus o 11% of older adults o Constant high pitched ringing or whistling sound in the ears Cues for Sound Localization  Interaural Time o Difference in arrival of sound to 2 ears  Interaural Intensity o Difference in volume of sound reaching 2 ears Chapter 6: Higher Perceptual Functions 2/18/2013 1:01:00 PM Object Recognition  Combining lower-level features into objects, interface between perception and memory  Agnosia- inability to recognize visual objects (they can still see, there is nothing wrong with their sensory processing. Lower levels of processing are intact, higher level is not there, they cannot put elements into coherent whole).  Can also result from impairment of link between visual perception and memory (specific to vision)  When a person touches it, he can immediately tell you what it is. When he perceives it, he cannot tell you what exactly it is, even though he knows what a teabag is. Patient G.S.  Had a stroke, and was left with agnosia.  He can name objects, but he had a deficit in recognition.  Could recognize what his fingers did. Where and What Pathways  Two major outputs from occipital lobe o Ventral Pathway (Inferior longitudinal fasiculus)  Deficits restricted to vision, anterior- visual memory, posterior- visual discrimination  Bilateral lesions required- if you only lesion one side, the remaining hemisphere can take over one function  Information can cross over  Info crosses via corpus callosum, combination lesions demonstrate this, less cross-over in dorsal stream (where pathway is more segregated) o Dorsal Pathway  What is Temporal, where is parietal?  Lesions in lobes and compare to controls o Landmark task vs. object discrimination task Physiological Support for the What-Where Distinction  Parietal Lobe Neurons o Large receptive fields o Many neurons have peripheral receptive fields  Ideal for detecting peripheral objects as soon as they enter the field of view  Less in the center or in the fovea, they detect the onset of a stimulus as it moves into our vision (when you get the most firing)  Tuned to stimulus onset  Inferior and Middle Temporal Lobe Neurons o Always encompasses the fovea, ideal for detecting objects (detects color) o Has very complex characteristics Human Neuroimaging Data  PET study (1995)  Changing the demands of the task  Spatial task o Is the spatial arrangement the same here as it is there? o Activation that is more dorsal in the parietal lobe  Recognition task o Are those the same three objects? o Activation that is more ventral in the temporal lobe Human Brain Lesion Studies  Case of Patient D.F. o Names of objects if given a description o Low level perceptional abilities o Severe visual agnosia  Uses more object centered information  Parietal Lobe Lesions (Where/How) o Relatively rare to get restricted lesions so there are a lot of other problems as well o Optic ataxia- difficulty using movements to help vision  Temporal/Occipital Lobe Lesions (What) o Cannot figure out what an object is- visual agnosia o Anomia- lost the storage area for what specific objects are o Prospagnosia- restricted to faces, cannot recognize facial structures Computational Problems in Object Recognition  Variability in Sensory Information o Object Constancy- able to recognize an object even with vast differences  View-Dependent or View-Invariant Recognition o Perception proceeds from analyzing a viewpoint’s information  We store information in semantic memory- experience of seeing “a bike at a certain angle”  Pros: Acts fast to recognize object because you have stored information  Cons: Relatively expensive in the amount of storage space you need o Sensory input defines basic properties, such as major and minor axes  Create a representation of what the object would look like if it was rotated  Pros: Efficient in terms of storage  Cons: Slower in terms of how fast you can recognize an object Do we have a neuron that responds to specific stimuli?  Hierarchy of lower level features to the point where specific stimuli cause neurons to fire  The “ensemble coding” theory o A number of features are present together o Different cells respond to different features Lesion Studies of Object Recognition  Visual Agnosia o Recognition can occur through other modalities such as touch and audition o Differentiate from memory loss or other problems (agnosia) o Differentiate from sensory loss  Subtypes of Agnosia o Apperceptive Agnosia  A failure to integrate features into a coherent whole, disconnect between perception and memory  Case Study (could not recognize these things)  Letters (except those composed of straight segments)  Could not copy drawings  Rectangles of equal areas oriented differently  Faces (including own) o Associative Agnosia  Normal visual representation that cannot be used to recognize objects Tests of Agnosia  Tests that would challenge the system that would make it more difficult to recognize the object (challenging)  Fragmented, deleted information Apperceptive Agnosia  Patients are having trouble with object constancy (car in the parking lot when it’s dark)  Tests of object constancy abilities: patients impaired o Changed lighting conditions on the stimulus Associative Agnosia  Overlapping drawings. The task is to give them crayons and have them color in the various objects.  Case Study- F.R. A. has a deficit in putting objects together Diagnosis  Requires categorization by semantic properties  Knows what the objects look like, but cannot connect the functions. He tends to match up things that “look” more similar, but they cannot match up the meaning of the object. Warrington’s model: Left hemisphere is important for semantic processes. Leads to associative agnosia, whereas the right hemisphere leads to apperceptive agnosia. 
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