Prof. Greg Francis1PSY 310: Sensory and Perceptual ProcessesPurdue UniversityProcessing streamsPSY 310Greg FrancisLecture 10A continuous surface infolded on itself.Purdue UniversityNeurophysiology We are working under the following hypothesis What we see is determined by the pattern of neuralactivity in the brain This leads to several interesting questions about theconnection between neurophysiology andperceptual experiencePurdue UniversityNeural patterns Spatial scenes lead to particular patterns of neuralactivityPurdue UniversityNeural patterns Different stimuli give rise to different neuralpatterns and thus different perceptsPurdue UniversityNeural patterns Different stimuli give rise to different neuralpatterns and thus different perceptsPurdue UniversityBeginning, not end It becomes clear that the orientated edges representation isthe beginning rather than the end of the neurophysiologicalrepresentation of information For example, all of the previous pictures can be described asphotos of tables But what is common about the neural representation? When can we say that we understand how a percept isrepresented in the brain?Prof. Greg Francis2PSY 310: Sensory and Perceptual ProcessesPurdue UniversityBrightness illusion Craik-O’Brien-Cornsweet effect Left rectangle looksbrighter than rightrectanglePurdue UniversityCOC illusion A cross-section of luminance of the image showswhat it is really like Why do we see it as we do?Purdue UniversityCOC illusion Consider the response of ganglion cells First to an image without an illusionPurdue UniversityCOC illusion Consider the response of ganglion cells First to an image without an illusionPurdue UniversityCOC illusion Consider the response of ganglion cells Second to an image with the illusionPurdue UniversityCOC illusion So why is our perceptual experience similar?True squaresCOC squaresProf. Greg Francis3PSY 310: Sensory and Perceptual ProcessesPurdue UniversityCOC illusion Compare the ganglion cell responses to the twodifferent imagesTrue squaresCOC squaresPurdue UniversityCOC illusion The neural patterns are very similar, which, in part, explainswhy the perceptual experience is very similarTrue squaresCOC squaresPurdue UniversityPerceiving patterns How does an arrangement of dots have anorientation?Purdue UniversityGlass patterns Take random dots, make a copy, shift in aparticular directionPurdue UniversityGlass patterns Take random dots, make a copy, shift in a particulardirectionPurdue UniversityGlass patterns Take random dots, make a copy, shift in a particulardirectionProf. Greg Francis4PSY 310: Sensory and Perceptual ProcessesPurdue UniversityGlass patterns Look at responses from orientation sensitive cellsPurdue UniversityGlass patterns Look at responses from orientation sensitive cells Compare to responses from real circlesPurdue UniversityTest the explanation Make two types of Glass patterns Orientationally tuned cells respond less selectively to thepattern on the rightPurdue UniversityHigher brain areas We could spend a lot of time relating perception toproperties of ganglion cells or orientation-sensitivecells But there are some perceptual experiences thatcan only be related to cells in other areas of thebrain Processing streams identify organization of brainPurdue UniversityAgnosia An inability to identify objects in the world Dr. P. (The Man Who Mistook His Wife for a Hat) Excellent musician and painter Became unable to recognize people’s faces Facial agnosia Speaker voices quickly lead to identification So did body movements Also “saw” faces where there were none Patting tops of fire hydrants as if they were small childrenPurdue UniversityAgnosia During examination could not put shoe back onfoot Was unsure which was the shoe and which wasthe footProf. Greg Francis5PSY 310: Sensory and Perceptual ProcessesPurdue UniversityDescribing a gloveWhat is this?’ I asked, holding up a glove.‘May I examine it?’ he asked, and, taking it from me, he proceeded to examine it as he had examined the geometricalshapes.‘A continuous surface,’ he announced at last, ‘infolded on itself. It appears to have’ –he hesitated – ‘five outpouchings, if this is the word.’‘Yes,’ I said cautiously. ‘You have given me a description. Now tell me what it is.’‘Acontainer of some sort?’‘Yes.’ I said, ‘and what would it contain?’‘It would contain its contents!’ said Dr P. with a laugh. ‘There are many possibilities. Itcould be a change-purse, for example, for coins of five sizes. It could…’I interruptedthe barmy flow.‘Does it not look familiar? Do you think it might contain, might fit, a part of yourbody?’No light of recognition dawned on his face. Later, by accident, he got it on, and exclaimed, ‘My God, it’s a glove!’Purdue UniversityBrain structure From visual cortex, information follows two pathsthrough the brainPurdue UniversityDorsal stream From visual cortex to the parietal lobe Involved in working with objectsPurdue UniversityVentral stream From visual cortex to the temporal lobe Involved in recognizing or identifying objectsPurdue UniversityPatient DF Similar to Dr. P, but studied more carefully For example, ask her to walk over barriers of various heights Not a problem, toe clearance was fairly normalPurdue UniversityPatient DF Now ask DF to order the barriers by height Absolutely horrible?Prof. Greg Francis6PSY 310: Sensory and Perceptual ProcessesPurdue UniversityPatient DF Similar behavior for another task Match the orientation of the card to be the sameas the slot Very difficult to do for DFPurdue UniversityPatient DF Similar behavior for another task Put the card into the slot Orientation matches just fine!Purdue UniversityDF’s brain Damage to theventral streamPurdue UniversityDF’s brain Damage to the ventral streamPurdue UniversityConclusions Relating perception to neurophysiologicalresponses Ganglion cells Orientation sensitive cells Other areas of the brain Processing streams Dorsal Ventral AgnosiaPurdue UniversityNext time Neural codes in the different streams Motion Object
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