the ventral stream and visual agnosia
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The Ventral Stream and Visual AgnosiaThe Ventral Stream and Visual Agnosia
David Glenn Clark, MD
Department of Neurology, UAB and BVAMC
David Glenn Clark, MD
Department of Neurology, UAB and BVAMC
OutlineOutline
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
Main PointsMain Points
The “ventral stream” refers to the flow of visual information from striate cortex toward the temporal poles
Lesions of the ventral stream induce disorders of complex visual processing
Receptive fields of neurons in the temporal lobe may be specific for certain semantic categories
The “ventral stream” refers to the flow of visual information from striate cortex toward the temporal poles
Lesions of the ventral stream induce disorders of complex visual processing
Receptive fields of neurons in the temporal lobe may be specific for certain semantic categories
What does it mean to see?What does it mean to see?
“To learn what is where by looking.” (Aristotle)
Marr, 1982: “Vision is the process of discovering from images what is present in the world, and where it is.”
“To learn what is where by looking.” (Aristotle)
Marr, 1982: “Vision is the process of discovering from images what is present in the world, and where it is.”
What does it mean to see?What does it mean to see?
“To learn what is where by looking.” (Aristotle)
Marr, 1982: “Vision is the process of discovering from images what is present in the world, and where it is.”
“To learn what is where by looking.” (Aristotle)
Marr, 1982: “Vision is the process of discovering from images what is present in the world, and where it is.”
where
what
Sources of InformationSources of Information
Artificial Intelligence How would you build a robot that brings you a
coke from the fridge?
Patients Lesion-symptom mapping
Functional imaging, EEG, MEG Non-human primate studies
Artificial Intelligence How would you build a robot that brings you a
coke from the fridge?
Patients Lesion-symptom mapping
Functional imaging, EEG, MEG Non-human primate studies
Why See?Why See?
If we want a robot to retrieve cokes or other beverages, it might help if it can see
Seeing (like all senses) appears to be useful only for guiding movements
Seeing helps us (and other animals) to: Identify tigers, cokes, enemies, potential mates Use this information to guide fleeing, drinking,
attacking, and mating calls
If we want a robot to retrieve cokes or other beverages, it might help if it can see
Seeing (like all senses) appears to be useful only for guiding movements
Seeing helps us (and other animals) to: Identify tigers, cokes, enemies, potential mates Use this information to guide fleeing, drinking,
attacking, and mating calls
What Our Robot Needs To AccomplishWhat Our Robot Needs To Accomplish
Process images from its environment: Lines, borders, shapes, solids, colors
Identify objects from processed images Maintain a representation of the environment
Multiple objects, spatial relationships among them
Represent itself within its environment Compute movements to manipulate objects based
on these representations
Process images from its environment: Lines, borders, shapes, solids, colors
Identify objects from processed images Maintain a representation of the environment
Multiple objects, spatial relationships among them
Represent itself within its environment Compute movements to manipulate objects based
on these representations
;; given a graphic scene, return ‘true’ if an object is present;; and ‘false’ if no object is present
(defun find_object (scene) …)
;; given a location and a graphic scene, find the nearest 90 ;; degree angle and return its location. Return false if there;; is no corner
(defun find_corner (x y scene) …)
;; given a scene, use find_corner to identify the locations of;; all corners and ensure that they are connected by lines
(defun find_4corners (scene) (let ((corner (find_corner (0 0 scene)))) …)
HOW VISION WORKS
HOW VISION WORKS
Advantages of NeuronsAdvantages of Neurons
Parallel processing Fault tolerant Fuzzy reasoning Form generalizations Permits cascading
neural events Top-down processing
Parallel processing Fault tolerant Fuzzy reasoning Form generalizations Permits cascading
neural events Top-down processing
OutlineOutline
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
Pointsand edges
Colors
Motion
Surfaces
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tool FaceAnimal Fruit
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tool FaceAnimal Fruit
HearingTactile sen. Gustation Emotion
OutlineOutline
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
Examining Ventral Stream Function
Examining Ventral Stream Function
Ensure that basic visual perception is normal Visual acuity Visual fields Brightness discrimination, edge detection, number of
stimuli, depth perception
Also assess: Color perception Motion processing
Ensure that basic visual perception is normal Visual acuity Visual fields Brightness discrimination, edge detection, number of
stimuli, depth perception
Also assess: Color perception Motion processing
Examining Ventral Stream Function
Examining Ventral Stream Function
Evaluate naming Visual confrontational naming
Line drawings, photographs, real objects, moving stimuli Various categories: faces, animals, artifacts, plants
Naming in other sensory modalities (tactile, auditory)
Verbal fluency Naming to definition Color naming
Evaluate naming Visual confrontational naming
Line drawings, photographs, real objects, moving stimuli Various categories: faces, animals, artifacts, plants
Naming in other sensory modalities (tactile, auditory)
Verbal fluency Naming to definition Color naming
Examining Ventral Stream Function
Examining Ventral Stream Function
Nonverbal evaluation of complex visual perception Matching Copying Verbal description of visual percepts
Semantic knowledge pertaining to percepts Can the patient recognize an object but not name it? Can the patient answer conceptual questions about
visual percepts or questions about concrete entities in the world?
Nonverbal evaluation of complex visual perception Matching Copying Verbal description of visual percepts
Semantic knowledge pertaining to percepts Can the patient recognize an object but not name it? Can the patient answer conceptual questions about
visual percepts or questions about concrete entities in the world?
OutlineOutline
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
What does it mean to see? Neural organization of visual processing Examination of ventral stream functions Brain lesions
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Central AchromatopsiaCentral Achromatopsia
A defect in color perception caused by an acquired cerebral lesion Reduced hue discrimination Deficient color constancy Cannot match colored plates Ishihara plates may help diagnosis
Lesion is in ventro-medial occipital lobe(s) Colors are either all gray, or “washed out”, “dirty”, or “faded” Some subjects report defective color imagery Also known as color agnosia
A defect in color perception caused by an acquired cerebral lesion Reduced hue discrimination Deficient color constancy Cannot match colored plates Ishihara plates may help diagnosis
Lesion is in ventro-medial occipital lobe(s) Colors are either all gray, or “washed out”, “dirty”, or “faded” Some subjects report defective color imagery Also known as color agnosia
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Apperceptive AgnosiaApperceptive Agnosia
Disruption of early image processing Cannot be explained by defects of visual fields, color vision,
brightness detection or other elementary visual processes Patients cannot:
Recognize visually presented objects Accurately describe shapes or features of visually presented items Copy figures Match figures
Most common with diffuse brain injury: CO or Hg poisoning At least one case after focal brain injury
Disruption of early image processing Cannot be explained by defects of visual fields, color vision,
brightness detection or other elementary visual processes Patients cannot:
Recognize visually presented objects Accurately describe shapes or features of visually presented items Copy figures Match figures
Most common with diffuse brain injury: CO or Hg poisoning At least one case after focal brain injury
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tool FaceAnimal Fruit
HearingTactile sen. Gustation Emotion
Associative AgnosiaAssociative Agnosia
“A normal percept stripped of its meanings” Disrupted activation of conceptual knowledge
after visual form is processed Patients CANNOT:
Recognize visually presented objects Patients CAN:
Recognize and name objects in other modalities Copy pictures of objects Match one picture to another
“A normal percept stripped of its meanings” Disrupted activation of conceptual knowledge
after visual form is processed Patients CANNOT:
Recognize visually presented objects Patients CAN:
Recognize and name objects in other modalities Copy pictures of objects Match one picture to another
Associative AgnosiaAssociative Agnosia
Lesions have various descriptions, but are predominantly in ventral stream Bilateral temporo-occipital with underlying
white matter Perhaps more common with right hemisphere
lesions when naming is unimpaired
Etiologies: stroke (PCA), AD, SD, DLB
Lesions have various descriptions, but are predominantly in ventral stream Bilateral temporo-occipital with underlying
white matter Perhaps more common with right hemisphere
lesions when naming is unimpaired
Etiologies: stroke (PCA), AD, SD, DLB
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tools FacesAnimals Fruits
HearingTactile sen. Gustation Emotion
ProsopagnosiaProsopagnosia
A deficit of face processing and recognition Lesion always temporo-occipital, probably
always right hemispheric Fusiform face area (R fusiform gyrus) Right temporal pole Left temporal pole seems to be necessary
for accurate face naming
A deficit of face processing and recognition Lesion always temporo-occipital, probably
always right hemispheric Fusiform face area (R fusiform gyrus) Right temporal pole Left temporal pole seems to be necessary
for accurate face naming
Faces Are SpecialFaces Are Special
One prosopagnosic patient could identify specific sheep better than specific people
Farah studied a patient who performed normally recalling pictures of objects (e.g., eyeglass frames) but not faces
Same subject showed better recognition memory of inverted faces relative to controls
One prosopagnosic patient could identify specific sheep better than specific people
Farah studied a patient who performed normally recalling pictures of objects (e.g., eyeglass frames) but not faces
Same subject showed better recognition memory of inverted faces relative to controls
Conscious vs. Emotional Face Processing
Conscious vs. Emotional Face Processing
Patients with prosopagnosia may still exhibit autonomic (GSR) response to familiar faces
Patients with intact facial recognition may lose autonomic responses to familiar or angry faces
Patients with prosopagnosia may still exhibit autonomic (GSR) response to familiar faces
Patients with intact facial recognition may lose autonomic responses to familiar or angry faces
Neuropsychiatric SyndromesNeuropsychiatric Syndromes
Misidentification Capgras - Invasion of the Body Snatchers Fregoli - Fallen (with Denzel Washington) Intermetamorphosis - Lost Highway,
Mulholland Drive
Visual Hallucinations DLB: well-formed, often animate, associated
with more Lewy bodies in temporal lobe
Misidentification Capgras - Invasion of the Body Snatchers Fregoli - Fallen (with Denzel Washington) Intermetamorphosis - Lost Highway,
Mulholland Drive
Visual Hallucinations DLB: well-formed, often animate, associated
with more Lewy bodies in temporal lobe
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tools FacesAnimals Fruits
HearingTactile sen. Gustation Emotion
words
Optic AphasiaOptic Aphasia
Lesion in ventral stream of language-dominant hemisphere
Patients show intact visual recognition but naming defect only in response to visual stimuli
(Pt. shown a key) “You open a door with it… it’s a… lock” (Pt. handed key) “It’s a key!”
Lesion in ventral stream of language-dominant hemisphere
Patients show intact visual recognition but naming defect only in response to visual stimuli
(Pt. shown a key) “You open a door with it… it’s a… lock” (Pt. handed key) “It’s a key!”
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
words
Pure AlexiaPure Alexia
Classically a L PCA infarction with R hemianopsia and damage to splenium of corpus callosum
AKA “Pure Word Blindness” Disorder of reading with generally intact
visual naming and other language functions
Classically a L PCA infarction with R hemianopsia and damage to splenium of corpus callosum
AKA “Pure Word Blindness” Disorder of reading with generally intact
visual naming and other language functions
Pointsand edges
Colors
Shapes
Motion
SolidsSurfaces
Tool FaceAnimal Fruit
HearingTactile sen. Gustation Emotion
Category Specific DeficitsCategory Specific Deficits
Numerous patients described with defective recognition or naming of concrete entities
Per Caramazza, always animals, plant matter, or conspecifics
Several competing hypotheses for explaining this
My personal favorite is Damasio’s Convergence Zone hypothesis
Numerous patients described with defective recognition or naming of concrete entities
Per Caramazza, always animals, plant matter, or conspecifics
Several competing hypotheses for explaining this
My personal favorite is Damasio’s Convergence Zone hypothesis
Convergence ZonesConvergence Zones
Entities within a semantic category have overlapping features
Association cortices capture statistical regularities in other cortical regions
Neurons with similar receptive fields tend to group together in associative maps
Leads to clustering of neurons that have relative specificity for a given category
Entities within a semantic category have overlapping features
Association cortices capture statistical regularities in other cortical regions
Neurons with similar receptive fields tend to group together in associative maps
Leads to clustering of neurons that have relative specificity for a given category
Main PointsMain Points
The “ventral stream” refers to the flow of visual information from striate cortex toward the temporal poles
Lesions of the ventral stream induce disorders of complex visual processing
Receptive fields of neurons in the temporal lobe may be specific for certain semantic categories
The “ventral stream” refers to the flow of visual information from striate cortex toward the temporal poles
Lesions of the ventral stream induce disorders of complex visual processing
Receptive fields of neurons in the temporal lobe may be specific for certain semantic categories
RecapitulationRecapitulation
Achromatopsia Apperceptive agnosia Associative agnosia Optic aphasia Pure alexia Category-specific semantic or lexical
defects
Achromatopsia Apperceptive agnosia Associative agnosia Optic aphasia Pure alexia Category-specific semantic or lexical
defects
Recommended ReadingRecommended Reading
Visual Agnosia (2004) - Martha Farah Vision (1982) - David Marr Neural systems behind word and concept retrieval
(2004) - Damasio, Cognition (92) pp. 179-229 Two hierarchically organized neural systems for
object information in human visual cortex (2008) - Konen, Nature Neuroscience (11) pp. 224-231
Visual Agnosia (2004) - Martha Farah Vision (1982) - David Marr Neural systems behind word and concept retrieval
(2004) - Damasio, Cognition (92) pp. 179-229 Two hierarchically organized neural systems for
object information in human visual cortex (2008) - Konen, Nature Neuroscience (11) pp. 224-231
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