The Ventral Stream and Visual Agnosia David Glenn Clark, MD Department of Neurology, UAB and BVAMC David Glenn Clark, MD Department of Neurology, UAB and.

The 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

Outline  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 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?  “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 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?  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 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

Advantages of Neurons  Parallel processing  Fault tolerant  Fuzzy reasoning  Form generalizations  Permits cascading neural events  Top-down processing

Points and edges Colors Motion Surfaces

Points and edges Colors Shapes Motion SolidsSurfaces

Points and edges Colors Shapes Motion SolidsSurfaces ToolFaceAnimalFruit

Points and edges Colors Shapes Motion SolidsSurfaces ToolFaceAnimalFruit HearingTactile sen.GustationEmotion

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  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  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?

Central 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

Apperceptive 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

Associative 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 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

Points and edges Colors Shapes Motion SolidsSurfaces ToolsFacesAnimalsFruits HearingTactile sen.GustationEmotion

Prosopagnosia  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 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  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 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

Points and edges Colors Shapes Motion SolidsSurfaces ToolsFacesAnimalsFruits HearingTactile sen.GustationEmotion words

Optic 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!”

Points and edges Colors Shapes Motion SolidsSurfaces words

Pure 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

Category 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 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 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

Recapitulation  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 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

The Ventral Stream and Visual Agnosia David Glenn Clark, MD Department of Neurology, UAB and BVAMC David Glenn Clark, MD Department of Neurology, UAB and.

Similar presentations

Presentation on theme: "The Ventral Stream and Visual Agnosia David Glenn Clark, MD Department of Neurology, UAB and BVAMC David Glenn Clark, MD Department of Neurology, UAB and."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

The Ventral Stream and Visual Agnosia David Glenn Clark, MD Department of Neurology, UAB and BVAMC David Glenn Clark, MD Department of Neurology, UAB and.

Similar presentations

Presentation on theme: "The Ventral Stream and Visual Agnosia David Glenn Clark, MD Department of Neurology, UAB and BVAMC David Glenn Clark, MD Department of Neurology, UAB and."— Presentation transcript:

Similar presentations

About project

Feedback