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1、Vision,Vision 1: Filling-in, Color, Motion, Form,Visual Paths Filling-In Perceptual Completion Conceptual Completion Color Motion Form Agnosia Prosopagnosia,Filling-In,Usually, function of a brain area is deduced from deficits correlated with damage to that area In the case of filling-in, brain func
2、tion is deduced 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:
3、Hemianopia,Perceptual Filling-In,Ramachandran patient: Filled in texture/surfaces but not objects Filled in numbers but looked like hieroglyphics/couldnt identify Filling in occurs at different speeds for different perceptual attributes Couldnt fill in faces,Lessons From Filling In: Perceptual Compl
4、etion,Brain uses statistical 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 Hallucinatio
5、ns Arent Real Because:,Others correct them Fade after a few seconds Highly improbably Something 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 pe
6、rception caused by an acquired cerebral 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 uncertain
7、Reduced hue discrimination Deficient color constancy Co-occurs often with alexia or visual agnosia V4 damage most likely site Lingual gyrus, fusiform gyrus, or white matter between the regions,V4 Damage,Disorder of Color Imagery,Seems that defective color perception invariably results in defective c
8、olor imagery Imagining an objects color (e.g., a yellow banana) requires an least some of the neural representations required to perceive color Patient cannot “remember” the color of items that need to be imagined,Color Agnosia Disorder Of Color Recognition,Perform fine on color matching tasks Exhib
9、it errors in matching colors to objects May still have semantic 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
10、by acquired cerebral lesions Because motion cues serve many purposes, a range of deficits can result E.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 targets Faster ones materialized at
11、successive positions with no movement in between Did not perceive apparent motion Reduced perception of motion after-effects Saw changes in position not depth for objects moved towards her *Motion after-effect illusion for demo,L.M. Case Description,Good static visual acuity perception Perception of
12、 tactile and acoustic motion Accurate localization of visual targets by saccadic eye movements No visual field defect for form No neglect of visual targets flashed simultaneously in both hemi field Relative preservation of face and object recognition, reading, and color vision,V5 Damage,Motion Blind
13、ness: Neuroanatomical Locus,Damage Parietal-temporo-occipital, near angular gyrus Parieto-occipital As 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 mon
14、keys area MT / V5) The homologies between motion processing areas in monkey and human may not 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,Visua
15、l Agnosia,Visual Object Agnosia,Apperceptive Associative,Apperceptive Agnosia,Intact vision: Acuity, brightness discrimination, color vision, & other elementary visual capabilities Sometimes preserved shape from motion Deficits: Abnormal shape perception (pictures, letters, simple shapes) Grouping p
16、rocess deficit (that operates over an array of local features representing contour, color, depth, etc.),Apperceptive Agnosia,VIDEO: Apperceptive Agnosia, impaired triangle recognition, subject 1 VIDEO: Apperceptive Agnosia, impaired object recognition, subject 1 VIDEO: Object Agnosia 2: Impaired Vis
17、ual but not tactile identification (naming), subject 2 VIDEO: Object Agnosia 3: Intact visual movement identification, subject 2 VIDEO: Object Agnosia 1: Impaired Visual identification (subject given name & array of objects), cant see objects,Associative Agnosia,Associative Agnosia Cannot recognize
18、objects by sight alone Intact general knowledge of objects Can recognize objects by touch or definition Visual perception better than in apperceptive agnosia Not a naming deficit (cannot indicate recognition by nonverbal means),Theories of Associative Agnosia,Disconnection between visual representat
19、ions and language areas Disconnection between visual representations and memory areas Stored visual memories have been damaged A perceptual and memory problem, and the two are inseparable,Intertwined Perception & Memory,Some visual problems Copying drawings on line by line On matching tasks, they re
20、ly on slow, sequential featured-by-feature checking In the PDP system, the memory of the stimulus would consist of a pattern of connections strengths among a number of neuron like units. The “ perceptual“ representation resulting from presentation of the stimulus will depend upon the pattern of conn
21、ection strengths among the units directly or indirectly activated by the stimulus. Thus, if a memory is altered by damaging the network, perception will be altered as well. Thus, Associative Agnosia may not be the results of an impairment to perception or to memory; rather, the two are in principle
22、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 experience.,Apperceptive: Localization of Damage,Diffuse brain damage, often from carbon monoxide poisoning,Apperceptive Associative,Ass
23、ociative Agnosia,Prosopagnosia,Prosopagnosia,Compensate by relying on nonfacial cues (voice, gait, clothing) With a few exceptions, they can discriminate a faces gender, ethnicity, approximate age, and emotion conveyed. Patients who do not have problems recognizing faces may have difficulty recogniz
24、ing the emotion.,Matching Faces Task,Test of Famous Faces,Skin Conductance Response (SCR),Farah Ch. 7: Are Faces Really Unique?,Types Of Agnosia,Face Object Printed Word Face, or face and object - right or bilateral Word, or word and object left Maximum overlap in left inferior medial region (including parahippocampal, fusiform, and lingual gyri),Capgras,Patients have both left and right hemisphere damage Possible Damage Sites: Disconnection between IT & amygdala (limbic system, emotion),