1、VisionVision 1:Filling-in,Color,Motion,Form Visual Paths Filling-In Perceptual Completion Conceptual Completion Color Motion Form Agnosia ProsopagnosiaFilling-In Usually,function of a brain area is deduced from deficits correlated with damage to that area In the case of filling-in,brain function is
2、deduced from intact abilities(perceptions)in the absence of sensory inputFilling-In:Perceptual CompletionPerceptual Completion in NormalslProbably due to excitatory horizontal connections in V1Filling-In Resulting From V1 Damage From scotomas(“hole”in V1)Hemianopias*DIGITAL VIDEO:Hemianopia Perceptu
3、al Filling-InRamachandran 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 facesLessons From Filling In:Perceptual Completionl Brain uses statisti
4、cal regularities to fill in.l This act of interpolation saves an enormous amount of computation.l Perhaps due to lateral horizontal connections in cortical areas higher than V1?Conceptual Completion Additional parietal damageCharles Bonnet SyndromePatients Know Hallucinations Arent Real Because:l Ot
5、hers correct theml Fade after a few secondsl Highly improbablyl Something odd about the images(too vivid,cartoonish,etc.)Lessons From Filling-In:Conceptual Completion Parietal Damage?Back-Projections?Disorders of Color ProcessingCentral Achromatopsia Deficit in color perception caused by an acquired
6、 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 fieldCentral Achromatopsia Disorder of Color Perception Nature of the impairment uncertain Reduced hue discrimination Deficien
7、t color constancy Co-occurs often with alexia or visual agnosia V4 damage most likely site Lingual gyrus,fusiform gyrus,or white matter between the regionsV4 DamageDisorder of Color Imagery Seems that defective color perception invariably results in defective color imagery Imagining an objects color
8、(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 imaginedColor Agnosia Disorder Of Color Recognition Perform fine on color matching tasks Exhibit errors in matching colors to objects May s
9、till have semantic knowledge about colors Not yet well-distinguished from color perception disorder Behavioral manifestations Site of damageCerebral Akinetopsia:Motion BlindnessCerebral Akinetopsia:Motion Blindness Deficit of motion processing caused by acquired cerebral lesions Because motion cues
10、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 impairedL.M.Case Description Could see slowly moving targets Faster ones materialized at successive positions with no movement in between Did no
11、t 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 demoL.M.Case Description Good static visual acuity perception Perception of tactile and acoustic motion Accurate localization of visu
12、al 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 visionV5 DamageMotion Blindness:Neuroanatomical Locus Damage Parietal-temporo-occipital,n
13、ear 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 monkeys area MT/V5)The homologies between motion processing areas in mon
14、key 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 cerebellumWHAT,WHERE,&HOW SYSTEMSWhat,Where,&How SystemsWhatVisual AgnosiaVisual Object Agnosia Apperceptive AssociativeApperceptive Agnosia Intact
15、vision:Acuity,brightness discrimination,color vision,&other elementary visual capabilities Sometimes preserved shape from motion Deficits:Abnormal shape perception(pictures,letters,simple shapes)Grouping process deficit(that operates over an array of local features representing contour,color,depth,e
16、tc.)Apperceptive Agnosia VIDEO:Apperceptive Agnosia,impaired triangle recognition,subject 1 VIDEO:Apperceptive Agnosia,impaired object recognition,subject 1 VIDEO:Object Agnosia 2:Impaired Visual but not tactile identification(naming),subject 2 VIDEO:Object Agnosia 3:Intact visual movement identific
17、ation,subject 2 VIDEO:Object Agnosia 1:Impaired Visual identification(subject given name&array of objects),cant see objectsAssociative AgnosiaAssociative Agnosia Cannot recognize objects by sight alone Intact general knowledge of objects Can recognize objects by touch or definition Visual perception
18、 better than in apperceptive agnosia Not a naming deficit(cannot indicate recognition by nonverbal means)Theories of Associative Agnosial Disconnection between visual representations and language areasl Disconnection between visual representations and memory areasl Stored visual memories have been d
19、amagedl A perceptual and memory problem,and the two are inseparableIntertwined Perception&MemorySome 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 c
20、onnections strengths among 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
21、,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 inseparable,and the impairment is better described as a loss of high level visual perceptual representations that were shaped by,and embody
22、the memory of,visual experience.Apperceptive:Localization of Damage Diffuse brain damage,often from carbon monoxide poisoningApperceptive AssociativeAssociative AgnosiaProsopagnosiaProsopagnosia Compensate by relying on nonfacial cues(voice,gait,clothing.)With a few exceptions,they can discriminate
23、a faces gender,ethnicity,approximate age,and emotion conveyed.Patients who do not have problems recognizing faces may have difficulty recognizing the emotion.Matching Faces TaskTest of Famous FacesSkin Conductance Response(SCR)Farah Ch.7:Are Faces Really Unique?Types Of Agnosia Face Object Printed W
24、ord 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)
