Vision

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Vision
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Vision 1 Filling-in, Color, Motion, Form

• Visual Paths
• Filling-In
• Perceptual Completion
• Conceptual Completion
• Color
• Motion
• Form
• Agnosia
• Prosopagnosia

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Filling-In

• Usually, function of a brain area is deduced from
  deficits correlated with damage to that area
• In the case of filling-in, brain function is
  deduced from intact abilities (perceptions) in
  the absence of sensory input

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Filling-In Perceptual Completion
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Perceptual Completion in Normals

• Probably due to excitatory horizontal connections
  in V1

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Filling-In Resulting From V1 Damage

• From scotomas (hole in V1)
• Hemianopias
• DIGITAL VIDEO Hemianopia

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Perceptual Filling-In

• Ramachandran patient
• Filled in texture/surfaces but not objects
• Filled in numbers but looked like
  hieroglyphics/couldnt identify
• Filling in occurs at different speeds for
  different perceptual attributes
• Couldnt fill in faces

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Lessons From Filling In Perceptual Completion

1. Brain uses statistical regularities to fill in.
2. This act of interpolation saves an enormous
   amount of computation.
3. Perhaps due to lateral horizontal connections in
   cortical areas higher than V1?

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Conceptual Completion

• Additional parietal damage

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Charles Bonnet Syndrome
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Patients Know Hallucinations Arent Real Because

• Others correct them
• Fade after a few seconds
• Highly improbably
• Something odd about the images (too vivid,
  cartoonish, etc.)

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Lessons From Filling-InConceptual Completion

• Parietal Damage?
• Back-Projections?

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Disorders of Color Processing
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Central Achromatopsia

• Deficit in color perception caused by an acquired
  cerebral lesion

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Tested With

• Color plate test
• (e.g., Ishihara Color Plate Test)
• Color arrangement test
• (e.g., Farnsworth-Munsell 100-Hue Test)
• Pass color chips across the visual field

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Central Achromatopsia Disorder of Color
Perception

•  Nature of the impairment uncertain
• Reduced hue discrimination
• Deficient color constancy
• Co-occurs often with alexia or visual agnosia
• V4 damage most likely site
• Lingual gyrus, fusiform gyrus, or white matter
  between the regions

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V4 Damage
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Disorder of Color Imagery

• Seems that defective color perception invariably
  results in defective color imagery
• Imagining an objects color (e.g., a yellow
  banana) requires an least some of the neural
  representations required to perceive color
• Patient cannot remember the color of items that
  need to be imagined

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Color Agnosia Disorder Of Color Recognition

• Perform fine on color matching tasks
• Exhibit errors in matching colors to objects
• May still have semantic knowledge about colors
• Not yet well-distinguished from color perception
  disorder
• Behavioral manifestations
• Site of damage

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Cerebral AkinetopsiaMotion Blindness
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Cerebral Akinetopsia Motion Blindness

• Deficit of motion processing caused by acquired
  cerebral lesions
• Because motion cues serve many purposes, a range
  of deficits can result
• E.g., Difficulty using motion to find objects
  (structure for motion or kinetic depth)
• Pursuit eye movements impaired

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L.M. Case Description

• Could see slowly moving targets
• Faster ones materialized at successive positions
  with no movement in between
• Did not perceive apparent motion
• Reduced perception of motion after-effects
• Saw changes in position not depth for objects
  moved towards her
• Motion after-effect illusion for demo

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L.M. Case Description

• Good static visual acuity perception
• Perception of tactile and acoustic motion
• Accurate localization of visual targets by
  saccadic eye movements
• No visual field defect for form
• No neglect of visual targets flashed
  simultaneously in both hemi field
• Relative preservation of face and object
  recognition, reading, and color vision

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V5 Damage
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Motion BlindnessNeuroanatomical Locus

• Damage
• Parietal-temporo-occipital, near angular gyrus
• Parieto-occipital
• As part of a more pervasive disturbance
• (Balint's syndrome or Alzheimer's disease)
• L M and others superior temporoparietal
• Includes the cortical areas of 19 and 37, which
  are adjacent (may resemble monkeys area MT / V5)
• The homologies between motion processing areas in
  monkey and human may not be as close as they once
  appeared.
• Severe deficits of motion perception can also
  occur with lesions in parietal insula and midline
  cerebellum

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WHAT, WHERE, HOW SYSTEMS
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What, Where, How Systems
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What
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Visual Agnosia
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Visual Object Agnosia

• Apperceptive
• Associative

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Apperceptive Agnosia

• Intact vision
• Acuity, brightness discrimination, color vision,
  other elementary visual capabilities
• Sometimes preserved shape from motion
• Deficits
• Abnormal shape perception (pictures, letters,
  simple shapes)
• Grouping process deficit (that operates over an
  array of local features representing contour,
  color, depth, etc.)

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Apperceptive Agnosia

• VIDEO Apperceptive Agnosia, impaired triangle
  recognition, subject 1
• VIDEO Apperceptive Agnosia, impaired object
  recognition, subject 1
• VIDEO Object Agnosia 2 Impaired Visual but not
  tactile identification (naming), subject 2
• VIDEO Object Agnosia 3 Intact visual movement
  identification, subject 2
• VIDEO Object Agnosia 1 Impaired Visual
  identification (subject given name array of
  objects), cant see objects

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Associative Agnosia

• Associative Agnosia
• Cannot recognize objects by sight alone
• Intact general knowledge of objects
• Can recognize objects by touch or definition
• Visual perception better than in apperceptive
  agnosia
• Not a naming deficit
• (cannot indicate recognition by nonverbal means)

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Theories of Associative Agnosia

1. Disconnection between visual representations and
   language areas
2. Disconnection between visual representations and
   memory areas
3. Stored visual memories have been damaged
4. A perceptual and memory problem, and the two are
   inseparable

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Intertwined Perception Memory

• Some visual problems
• Copying drawings on line by line
• On matching tasks, they rely on slow, sequential
  featured-by-feature checking
• In the PDP system, the memory of the stimulus
  would consist of a pattern of connections
  strengths among a number of neuron like units.
  The " perceptual" representation resulting from
  presentation of the stimulus will depend upon the
  pattern of connection strengths among the units
  directly or indirectly activated by the stimulus.
  Thus, if a memory is altered by damaging the
  network, perception will be altered as well.
  Thus, Associative Agnosia may not be the results
  of an impairment to perception or to memory
  rather, the two are in principle inseparable, and
  the impairment is better described as a loss of
  high level visual perceptual representations that
  were shaped by, and embody the memory of, visual
  experience.

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ApperceptiveLocalization of Damage

• Diffuse brain damage, often from carbon monoxide
  poisoning

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Apperceptive Associative
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Associative Agnosia
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Prosopagnosia
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Prosopagnosia

• Compensate by relying on nonfacial cues (voice,
  gait, clothing..)
• With a few exceptions, they can discriminate a
  faces gender, ethnicity, approximate age, and
  emotion conveyed.
• Patients who do not have problems recognizing
  faces may have difficulty recognizing the
  emotion.

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Matching Faces Task
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Test of Famous Faces
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Skin Conductance Response (SCR)
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Farah Ch. 7 Are Faces Really Unique?
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Types Of Agnosia

• Face
• Object
• Printed Word
• Face, or face and object -- right or bilateral
• Word, or word and object left
• Maximum overlap in left inferior medial region
  (including parahippocampal, fusiform, and lingual
  gyri)

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Capgras

• Patients have both left and right hemisphere
  damage
• Possible Damage Sites
• Disconnection between IT amygdala (limbic
  system, emotion)