Vision - UCSD Cognitive Science视觉-加州大学圣地亚哥分校的认知科学

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 functi

2、on is deduced from intact abilities (perceptions) in the absence of sensory inputfilling-in: perceptual completionperceptual completion in normals1.probably due to excitatory horizontal connections in v1filling-in resulting from v1 damage from scotomas (“hole” in v1) hemianopias *digital video: hemi

3、anopia perceptual 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 completion1. br

4、ain uses statistical regularities to fill in.2. this act of interpolation saves an enormous amount of computation.3. perhaps due to lateral horizontal connections in cortical areas higher than v1?conceptual completion additional parietal damagecharles bonnet syndromepatients know hallucinations aren

5、t real because:1. others correct them2. fade after a few seconds3. highly improbably4. 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 perce

6、ption 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 fieldcentral achromatopsia disorder of color perception nature of the impairment uncertain redu

7、ced 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 regionsv4 damagedisorder of color imagery seems that defective color perception invariably results in defective color i

8、magery 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 imaginedcolor agnosia disorder of color recognition perform fine on color matching tasks exhibit erro

9、rs in matching colors to objects may still 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 acquire

10、d 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 impairedl.m. case description could see slowly moving targets faster ones materialized at successive

11、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 demol.m. case description good static visual acuity perception perception of tactile and

12、 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 visionv5 damagemotion blindness:neuroanat

13、omical 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 monkeys area mt /

14、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 cerebellumwhat, where, & how systemswhat, where, & how systemswhatvisual agnosiavi

15、sual object agnosia apperceptive associativeapperceptive 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 process de

16、ficit (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 visual but no

17、t 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 objectsassociative agnosiaassociative agnosia cannot recognize objects

18、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 agnosia1. disconnection between visual representations an

19、d language areas2. disconnection between visual representations and memory areas3. stored visual memories have been damaged4. a perceptual and memory problem, and the two are inseparableintertwined perception & memorysome visual problems copying drawings on line by lineon matching tasks, they re

20、ly on slow, sequential featured-by-feature checkingin 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 connecti

21、on 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 inse

22、parable, 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 poisoningapperceptive associativeassociative agnosiaprosopagnosiaprosopagnosia compensa