1. Visuospatial Function
Review of Visual Neuroanatomy
Hierarchical organization and somatotopic, functional segregation of visual information from retina to cortex
Magnocellular (dorsal, ‘how/where’ pathway)
Parvocellular (ventral, ‘what’ pathway)
Disorders of higher-order visual function and how they are assessed
Variants of Blindness (Pre-striate and Striate Syndromes)
Ventral (‘what’) Stream Syndromes
Dorsal (‘where’) Stream Syndromes

2. Organizing Principles of Visual System
Somatotopy
Spatial relations in environment map to primary cortical areas that represent them
Hierarchy
information is summarized and passed on to higher levels in simplified form
information modified/combined at next level
final output reflects total information in system
Functional segregation
Lower level features are integrated into higher level representations of objects and location
objects in space are further integrated into meaningful environmental ‘scenes’
Parallel processing across hierarchical and functionally segregated systems (‘cross-talk’) ensures smooth integration of information

3. P P Anatomy of the eye Cornea Pupil Lens Retina Fovea Optic nerve
Outer layer of eye
Pupil
Aperture through which light enters eye
Lens
Focuses light on fovea
Retina
Layer of cells which process light
Fovea
Focal point of images
Optic nerve
Transmits visual information to brain P P

4. Rods Cones Fovea absent from fovea
high concentration in periphery of retina
low resolution (acuity)
respond to movement, orientation
primary input from ganglion cells to magnocellular pathways
high concentration in fovea
lower concentration in periphery of retina
high resolution (acuity)
respond to color, edges
primary input from ganglion cells to parvocellular pathways

5. Somatotopic Representation of Visual Information
The left LGN receives input from the right visual field via
nasal half of retina of right eye
temporal half of retina of left eye
The right LGN receives input from the left visual field via
nasal half of retina of left eye
temporal half of retina of right eye
Each LGN projects to the same-side (ipsilateral) primary visual cortex.
Objects in right visual field are processed in left visual cortex
Objects in left visual field are processed in right visual cortex
Left
Visual
Field
Right
Visual
Field
Temporal
Nasal
Temporal
Optic nerve
Optic chiasm
Optic tract
Lateral
geniculate
nucleus
Optic radiation
Primary visual cortex

6. Hierarchical processing From Retina to Cortex
Photoreceptors sensitive to four primary types of visual attributes
Attributes individually processed in photoreceptors
Color & shape (cones)
Orientation & movement (rods)
Photoreceptors connect to retinal ganglion cells which respond to only one of the attributes.
The ganglion cells forward their signals to cells in different layers of the lateral geniculate nucleus (LGN). These respond uniquely to that one type of information
LGN cells forward information to primary visual cortex and further cortical areas.
A complete and dynamic visual scene is assembled at higher levels

8. Functional Segregation of the Visual System
Multimodal
Parietal Cortex
Magnocellular Pathway
(responsive to movement & orientation) MT V3 V2
Dorsal Pathway
(‘where’) V1
M-ganglion cell
(info from rods)
Magno LGN
P-ganglion cell
(info from cones)
Parvo LGN V1
Ventral Pathway
(‘what’) V2
Parvocellular Pathway
(responsive to color & shape) V4 IT
Multimodal
Temporal Cortex

9. Hierarchical Organization of Visual System
Area
Neurons Respond to V1
colors, angled lines V2
linear motion, changes in depth V3
shapes, specific velocities of motion V4
complex patterns & shapes MT
optic flow (movement through environment)

10. Segregation of dorsal and ventral streams
Propagation of visual information from primary sensory cortex to multimodal integrative cortex
Dorsal stream continues superiorly ending in posterior parietal cortex
Ventral stream continues inferiorly ending in inferotemporal cortex
Not mutually exclusive- much cross talk between these processing streams.

13. Is the Hierarchy accidental?
Yamins, D. L., & DiCarlo, J. J. (2016), Using goal-driven deep learning models to understand sensory cortex. Nature neuroscience

14. Is the Hierarchy accidental?
Yamins, D. L., & DiCarlo, J. J. (2016), Using goal-driven deep learning models to understand sensory cortex. Nature neuroscience

15. Disorders of Visual Abilities
Primary Visual (striate/peri-striate cortex)
Primary Blindness/Visual field defects
Blindsight
Visuoperceptual (ventral ‘what’ stream)
Impairment of visual object/feature recognition (agnosias)
Defective visual feature analysis and synthesis
Visuospatial (dorsal ‘where’ stream)
Defective somatic and topographical orientation
Defective judgment of direction and distance
Visual attention deficits
Visuoconstructive (Sensory-Motor Integration)
Defective assembling performance
Defective drawing performance

16. Primary Visual Syndromes (Pre-Striate and Striate)
Blindness/Visual Field defect
failure to respond to information presented to visual field
damage between retina and V1
Monocular
Blindness
Tunnel Vision
Homonymous
Hemianopsia
Superior
Quadrantanopsia
Inferior
Quadrantanopsia
Superior
Quadrantanopsia

17. Primary Visual Syndromes (Pre-Striate and Striate)
Blindness/Visual Field defect
failure to respond to information presented to visual field
damage between retina and V1
‘Blind-sight’
ability to respond to visual stimuli in scotoma (‘blind spot’) without overt awareness
describe characteristics of objects
adjust grasping movement to location/size
avoid objects in path
semantic priming
Proposed mechanism: damage to V1, but preserved LGN or collicular input to higher visual association areas

18. Ventral Stream (‘What’) Disorders (Posterior Temporal / Inferior-Parietal Damage)
Associative visual Agnosia –
inability to recognize an object or its distinguishing feature(s)
inability is not explained by other deficits (e.g., sensory, language, attentional)
Deficit in assigning meaning to object
Apperceptive visual agnosia
Can describe, reproduce or discriminate objects in normal context
Changing orientation or context disrupts this ability
Deficit in visual perception

19. Gollin Incomplete Figures

20. Ventral Stream (‘What’) Disorders (Posterior Temporal Inferior-Parietal Damage)
Associative Visual Agnosia –
inability to associate visual forms with meaning
visual-perceptual and constructive functions (discrimination, matching, copying) are preserved
deficit in connecting visual information with semantic system
may affect verbal label only (anomia) or other semantic information (agnosia)
can be specific to physical features
Color
Letter/word forms (alexia)
Objects within a class (faces, cars, cows, bird species) (prosopagnosia)

22. Benton Facial Recognition Test
Famous Faces Test
David Letterman
Barack Obama
George Bush
Tiger Woods or
Talk-show Host
Current president
Former president
Golfer

23. WAIS-III Picture Completion
Ventral Stream (‘What’) Disorders (Posterior Temporal Inferior-Parietal Damage)
Defective visual analysis and synthesis
inability to discriminate/integrate abstract or meaningful visual features
may reflect primary visual-perceptual or attention deficits
subtle deficits may interfere with important functions (e.g. driving)
WAIS-III Picture Completion

24. Hooper Visuospatial Organization Test

25. WAIS-IV Matrix Reasoning

26. Dorsal Stream (‘Where’) Disorders (Superior Parietal Damage)
Deficits in Spatial Orientation
Intrapersonal
Right - left confusion (difficulty discriminating left and right on self or others)
Finger agnosia (difficulty discriminating fingers)
Anosagnosia (lack of awareness of motor deficit)
Extrapersonal
Topographic disorientation (inability to represent extrapersonal space)
Deficits of Visual Attention (another lecture)
Visual neglect
Balint’s Syndrome

27. R/L Orientation

28. Topographical Disorientation
Disruption of mental representation of environment within and beyond range of immediate perception
(Aguirre & D’Esposito, Brain, 1999)

29. Double Dissociation of Topographic Disorders
Egocentric Disorientation
‘Landmark’ Agnosia
Visual Object Recognition
Intact
Impaired (subtle)
Way-finding (Landmarks)
Not assessed
Impaired
Spatial Span
Visual Reaching
Judging Relative Position
Verbal Route Description
Way-finding (Spatial Map)
Lesion lateralization
Bilat or Right
Lesion localization
Posterior parietal
Lingual, fusiform, parahippocampal gyri

30. Visuo-Constructional Deficits (Frontal and/or Parietal Damage)
Deficit in reproducing 2D/3D representations of complex objects
Drawing tasks (Cross, Clock, Rey-Osterreith Figure)
Construction Tasks (WAIS-III Block Design

31. WAIS Block Design

32. Broken Configuration Error

33. 3D Constructional Tasks
Patient’s Reproduction
Model

34. Summary
Visual information is represented in the brain in somatotopic, hierarchically organized, functionally segregated (‘what’ and ‘where’) systems
Localized brain lesions produce dissociations between and within these systems, due to damage to specific functional subsystems
Apperceptive vs. Associative Agnosias
Category-specific agnosias