Occipital Lobes

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Bryan Kolb Ian Q. Whishaws
Fundamentals of Human Neuropsychology, Sixth
Edition Chapter 13 Lecture PPT
Prepared by Gina Mollet, Adams State College
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The Occipital Lobes
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Portrait An Injured Soldiers Visual World

• P.M.
• Struck by a bullet in the back of his brain
• Lost sight in the right visual field
• Could accurately guess about the presence or
  absence of light
• Difficulty reading and recognizing faces

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Anatomy of the Occipital Lobes

• No clear division on lateral surface of brain
• Medial Surface
• Parieto-occipital surface
• Calcarine Sulcus
• Contains much of primary visual cortex
• Separates upper and lower visual fields
• Ventral Surface
• Lingual gyrus
• V2 and VP
• Fusiform gyrus
• V4

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Subdivisions of the Occipital Cortex

• Map based on monkey occipital cortex

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Subdivisions of the Occipital Cortex

• Roger Tootell
• Map of human cortex

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Subdivisions of the Occipital Cortex

• Area V1
• Laminar organization most distinct of all
  cortical areas
• Heterogenous
• Has more than one distinct function
• Preserved in V2
• Striate cortex
• Another name for visual cortex due to its striped
  appearance

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Subdivisions of the Occipital Cortex

• Color Vision
• Primary job of V4, but distributed throughout
  occipital cortex
• Plays a role in detection of movement, depth, and
  position

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Connections of the Visual Cortex

• Connections
• Primary Visual Cortex (V1)
• Input from LGN
• Output to all other levels
• Secondary Visual Cortex (V2)
• Output to all other levels
• After V2
• Output to the parietal lobe - Dorsal Stream
• Output to the inferior temporal lobe - Ventral
  Stream
• Output to the superior temporal sulcus (STS) -
  STS Stream

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Visual Pathways

• Dorsal Stream
• Visual Guidance of Movements
• Ventral Stream
• Object Perception
• STS
• Visuospatial functions

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A Theory of Occipital Lobe Function

• Vision begins in V1 (primary visual cortex), that
  is heterogeneous, and then travels to more
  specialized cortical zones
• Selective lesions up the hierarchy produce
  specific visual deficits
• Lesions to V1 are not aware of seeing

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Visual Functions Beyond the Occipital Lobe

• Vision-related areas in the brain make up about
  55 of the total cortex
• Multiple visual regions in the temporal,
  parietal, and frontal lobes
• Vision
• Not unitary, composed of many quite specific
  forms of processing
• Five categories for vision

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Five Categories of Vision

• Vision for Action
• Parietal Visual Areas in the Dorsal Stream
• Reaching
• Ducking
• Catching
• Action for Vision
• Visual Scanning
• Eye Movements and Selective Attention

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Categories of Vision

• Visual Recognition
• Temporal Lobes
• Object Recognition
• Visual Space
• Parietal and Temporal Lobes
• Spatial location
• Location of an object relative to person
  (egocentric space)
• Location of an object relative to another
  (allocentric space)

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Categories of Vision

• Visual Attention
• Selective attention for specific visual input
• Parietal lobes guide movements and temporal lobes
  help in object recognition

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Visual Pathways Beyond the Occipital Lobe

• Milner and Goodale
• The dorsal stream is a set of systems for on-line
  visual control of action
• Evidence
• Visual neurons in the parietal cortex are active
  only when the brain acts on visual information
• 3 pathways run from V1 to the parietal cortex,
  must be functionally dissociable
• Visual impairments after parietal lesions can be
  characterized as visuomotor or orientational

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Visual Pathways Beyond the Occipital Lobe

• STS stream
• Characterized by polysensory neurons
• Neurons are responsive to both auditory and
  visual input or both visual and somatosensory
  input
• Originates from structures in the parietal and
  temporal cortex

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Imaging Studies of Dorsal and Ventral Streams

• Haxby and colleagues
• PET study
• Found activation for facial stimuli in the
  temporal region and activation during a location
  task in the posterior parietal region and frontal
  lobes
• Detection of motion activated V5, while detection
  of shape activated the STS
• Color perception activated area V4

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Disorders of Visual Pathways

• Monocular Blindness
• Loss of sight in one eye
• Results from destruction of the retina or optic
  nerve
• Bitemporal Hemianopia
• Loss of vision from both temporal fields
• Results from a lesion to the optic chiasm
• Nasal Hemianopia
• Loss of vision of one nasal field
• Results from a lesion of the lateral chiasm

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Disorders of Visual Pathways

• Homonymous Hemianopia
• Blindness of one entire visual field
• Results from a complete cut of the optic tract,
  LGN or V1
• Macular sparing
• Sparing of the central or macular region of the
  visual field
• Results from a lesion to the occipital lobe

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Disorders of Visual Pathways

• Quadrantoanopia or Hemianopia
• Complete loss of vision in one-quarter of the
  fovea or in one-half of the fovea
• Results from a lesion to the occipital lobe
• Field Defects
• Scotomas - small blind spots
• Results from small lesions to the occipital lobe

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Disorders of Cortical Function

• B.K. V1 Damage and a Scotoma
• Right infarct (dead tissue) in the occipital lobe
• Experienced blindsight - could perceive location
  without perceiving content
• Lost one-quarter of the fovea, poor vision in the
  upper left quadrant
• Slow facial recognition

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Disorders of Cortical Function

• Case D.B. V1 Damage and Blindsight
• Had an angioma in the right calcarine fissure
• Has a hemianopia
• Cortical Blindness - blindsight in which he
  reports no conscious awareness of seeing but can
  report movement and location of objects

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Disorders of Cortical Function

• Case J.I. V4 Damage and Loss of Color Vision
• Sustained a concussion and suddenly lost color
  vision
• Specific damage in the occipital cortex
• Improved acuity at twilight or at night
• Years later, no longer remembered color

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Disorders of Cortical Function

• Case P.B. Conscious Color Perception in a Blind
  Patient
• Suffered an ischemia that destroyed large area of
  the posterior cortex
• Can only detect presence or absence of light and
  has intact color vision

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Disorders of Cortical Function

• Case L.M. V5 (MT) Damage and the Perception of
  Movement
• Vascular abnormality that produced bilateral
  posterior damage
• Loss of movement vision
• Unable to intercept moving objects by using her
  hand

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Disorders of Cortical Function

• Case D.F. Occipital Damage and Visual Agnosia
• Bilateral damage to the LO region and tissue
  between the parietal and occipital lobes
• Visual form agnosia - inability to recognize line
  drawings of objects
• Can use visual information to guide movements,
  but not to recognize objects

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Disorders of Cortical Function

• Case V.K. Parietal Damage and Visuomotor
  Guidance
• Bilateral hemorrhages in the occipitoparietal
  regions
• Optic Ataxia - Deficit in visually guided hand
  movements

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Disorders of Cortical Function

• Cases D. and T. Higher-Level Visual Processes
• D
• Right occipitotemporal lesion
• Prosopagnosia - Facial recognition deficit
• Could read lips
• T
• Left occipitotemporal lesion
• Alexia - Inability to read
• Impaired lip reading

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Conclusions from Case Studies

• Distinct syndromes of visual disturbance
• Some provide evidence for a fundamental
  dissociation between the dorsal and ventral
  streams
• Visual experience is not unified
• Asymmetry in functions of occipital lobes

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Visual Agnosia

• Object Agnosia
• Apperceptive Agnosia
• Deficit in the ability to develop a percept of
  the structure of an object or objects
• Simultagnosia
• Unable to perceive more than one object at a time
• Results from bilateral damage to the lateral
  parts of the occipital lobes
• Associative Agnosia
• Can perceive objects, but cannot identify them
• Results from lesions to the anterior temporal
  lobes

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Visual Agnosia

• Other Agnosias
• Prosopagnosia
• Cannot recognize faces
• Can recognize facial features, facial
  expressions, and tell human from nonhuman faces
• Alexia
• Inability to read
• Form of object agnosia - inability to construct
  perceptual wholes from parts or
• Form of associative agnosia - word memory is
  damaged or inaccessible
• Results from damage to the left fusiform and
  lingual areas

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Visual Imagery

• Neural structures mediating perception and
  visualization are not completely independent
• Right hemisphere superiority in mental rotation
• Evidence that the left temporal-occipital region
  is responsible for image generation

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Snapshot Generating Mental Images

• Mark DEsposito and colleagues
• What is the neural basis for visual imagery?
• fMRI study
• Found that visualization of concrete words
  increases activation in the left posterior
  temporal-occipital region
• Findings consistent with other imaging studies
  and case studies

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