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1、Vision,Vision 1:Filling-in,Color,Motion,Form,Visual PathsFilling-InPerceptual CompletionConceptual CompletionColorMotionFormAgnosiaProsopagnosia,Filling-In,Usually,function of a brain area is deduced from deficits correlated with damage to that areaIn the case of filling-in,brain function is deduced
2、 from intact abilities(perceptions)in the absence of sensory input,Filling-In:Perceptual Completion,Perceptual Completion in Normals,Probably due to excitatory horizontal connections in V1,Filling-In Resulting From V1 Damage,From scotomas(“hole”in V1)Hemianopias*DIGITAL VIDEO:Hemianopia,Perceptual F
3、illing-In,Ramachandran patient:Filled in texture/surfaces but not objectsFilled in numbers but looked like hieroglyphics/couldnt identifyFilling in occurs at different speeds for different perceptual attributesCouldnt fill in faces,Lessons From Filling In:Perceptual Completion,Brain uses statistical
4、 regularities to fill in.This act of interpolation saves an enormous amount of computation.Perhaps due to lateral horizontal connections in cortical areas higher than V1?,Conceptual Completion,Additional parietal damage,Charles Bonnet Syndrome,Patients Know Hallucinations Arent Real Because:,Others
5、correct themFade after a few secondsHighly improbablySomething odd about the images(too vivid,cartoonish,etc.),Lessons From Filling-In:Conceptual Completion,Parietal Damage?Back-Projections?,Disorders of Color Processing,Central Achromatopsia,Deficit in color perception caused by an acquired cerebra
6、l lesion,Tested With,Color plate test(e.g.,Ishihara Color Plate Test)Color arrangement test(e.g.,Farnsworth-Munsell 100-Hue Test)Pass color chips across the visual field,Central Achromatopsia Disorder of Color Perception,Nature of the impairment uncertainReduced hue discrimination Deficient color co
7、nstancyCo-occurs often with alexia or visual agnosiaV4 damage most likely siteLingual gyrus,fusiform gyrus,or white matter between the regions,V4 Damage,Disorder of Color Imagery,Seems that defective color perception invariably results in defective color imageryImagining an objects color(e.g.,a yell
8、ow banana)requires an least some of the neural representations required to perceive colorPatient cannot“remember”the color of items that need to be imagined,Color Agnosia Disorder Of Color Recognition,Perform fine on color matching tasksExhibit errors in matching colors to objectsMay still have sema
9、ntic knowledge about colors Not yet well-distinguished from color perception disorder Behavioral manifestations Site of damage,Cerebral Akinetopsia:Motion Blindness,Cerebral Akinetopsia:Motion Blindness,Deficit of motion processing caused by acquired cerebral lesionsBecause motion cues serve many pu
10、rposes,a range of deficits can resultE.g.,Difficulty using motion to find objects(structure for motion or kinetic depth)Pursuit eye movements impaired,L.M.Case Description,Could see slowly moving targetsFaster ones materialized at successive positions with no movement in betweenDid not perceive appa
11、rent motionReduced perception of motion after-effectsSaw changes in position not depth for objects moved towards her*Motion after-effect illusion for demo,L.M.Case Description,Good static visual acuity perceptionPerception of tactile and acoustic motionAccurate localization of visual targets by sacc
12、adic eye movementsNo visual field defect for formNo neglect of visual targets flashed simultaneously in both hemi field Relative preservation of face and object recognition,reading,and color vision,V5 Damage,Motion Blindness:Neuroanatomical Locus,Damage Parietal-temporo-occipital,near angular gyrus
13、Parieto-occipitalAs part of a more pervasive disturbance(Balints syndrome or Alzheimers disease)L M and others:superior temporoparietal Includes the cortical areas of 19 and 37,which are adjacent(may resemble monkeys area MT/V5)The homologies between motion processing areas in monkey and human may n
14、ot be as close as they once appeared.Severe deficits of motion perception can also occur with lesions in parietal insula and midline cerebellum,WHAT,WHERE,&HOW SYSTEMS,What,Where,&How Systems,What,Visual Agnosia,Visual Object Agnosia,ApperceptiveAssociative,Apperceptive Agnosia,Intact vision:Acuity,
15、brightness discrimination,color vision,&other elementary visual capabilitiesSometimes preserved shape from motionDeficits:Abnormal shape perception(pictures,letters,simple shapes)Grouping process deficit(that operates over an array of local features representing contour,color,depth,etc.),Apperceptiv
16、e Agnosia,VIDEO:Apperceptive Agnosia,impaired triangle recognition,subject 1VIDEO:Apperceptive Agnosia,impaired object recognition,subject 1VIDEO:Object Agnosia 2:Impaired Visual but not tactile identification(naming),subject 2VIDEO:Object Agnosia 3:Intact visual movement identification,subject 2VID
17、EO:Object Agnosia 1:Impaired Visual identification(subject given name&array of objects),cant see objects,Associative Agnosia,Associative AgnosiaCannot recognize objects by sight aloneIntact general knowledge of objectsCan recognize objects by touch or definitionVisual perception better than in apper
18、ceptive agnosia Not a naming deficit(cannot indicate recognition by nonverbal means),Theories of Associative Agnosia,Disconnection between visual representations and language areasDisconnection between visual representations and memory areasStored visual memories have been damagedA perceptual and me
19、mory problem,and the two are inseparable,Intertwined Perception&Memory,Some visual problems Copying drawings on line by lineOn matching tasks,they rely on slow,sequential featured-by-feature checkingIn the PDP system,the memory of the stimulus would consist of a pattern of connections strengths amon
20、g a number of neuron like units.The perceptual representation resulting from presentation of the stimulus will depend upon the pattern of connection strengths among the units directly or indirectly activated by the stimulus.Thus,if a memory is altered by damaging the network,perception will be alter
21、ed as well.Thus,Associative Agnosia may not be the results of an impairment to perception or to memory;rather,the two are in principle inseparable,and the impairment is better described as a loss of high level visual perceptual representations that were shaped by,and embody the memory of,visual expe
22、rience.,Apperceptive:Localization of Damage,Diffuse brain damage,often from carbon monoxide poisoning,Apperceptive Associative,Associative Agnosia,Prosopagnosia,Prosopagnosia,Compensate by relying on nonfacial cues(voice,gait,clothing.)With a few exceptions,they can discriminate a faces gender,ethni
23、city,approximate age,and emotion conveyed.Patients who do not have problems recognizing faces may have difficulty recognizing the emotion.,Matching Faces Task,Test of Famous Faces,Skin Conductance Response(SCR),Farah Ch.7:Are Faces Really Unique?,Types Of Agnosia,FaceObjectPrinted WordFace,or face and object-right or bilateralWord,or word and object leftMaximum overlap in left inferior medial region(including parahippocampal,fusiform,and lingual gyri),Capgras,Patients have both left and right hemisphere damagePossible Damage Sites:Disconnection between IT&amygdala(limbic system,emotion),
