The Ventral Stream and Visual Agnosia

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


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




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.”



What does it mean to see?What does it mean to see?





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

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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


HearingTactile sen. Gustation Emotion

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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



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



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



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



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


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


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



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







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

Documents

The Ventral Stream and Visual Agnosia