Visual system

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Visual system
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fMRI of the Visual System

• Functional anatomy
• V1-V4
• MT and Dorsal Stream
• LO, IT, Ventral Stream
• E.G.s of Functional characterization
• Contours in V1-gt LO
• Organization in LO IT

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Retinotopy Stimulus
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Retinotopy Results in V1 Slice
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Retinotopy Unfolded results
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Selective attention to shape, color, motion
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V419 near 37
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Motion MT- V5
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• 39/19

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• 19/39 MT V5

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Object presentation

• Fusiform- 37

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Levy et al. Methods

• Stimuli Faces, houses center, periphery

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Disorders of visual perception

• Scotoma- loss in retinotopic representation V1-2
• Achromatopsia V4 lesion
• Akinetopsia V5 lesion
• Agnosia
• Object agnosia
• Prosopanosia
• Letter agnosia/pure alexia
• Anomia vs agnosia?

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Agnosia a loss of ability to recognize objects,
persons, sounds, shapes, or smells while the
specific sense is not defective nor is there any
significant memory loss.
Apperceptive agnosia -unable to distinguish
visual shapes and - have trouble recognizing,
copying, or discriminating between different
visual stimuli. - unable to copy
images Associative agnosia -Inability to
recognize objects -retain semantic knowledge
-can describe visual info, can copy
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Prosopagnosia Inability to recognize or
discriminate faces Found in RH or bilateral
lesions Lateral Fusiorm FFA lesions
Integrative agnosia or Simultanagnosia can
recognize 1 element at a time, cannot Process
more than 1 element or integrate elements into
a whole percept
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Higher level vision what vs where
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Higher level vision- what system

• V2 secondary vision stereopsis
• V3 form
• V4 color, color/shape
• V5 motion- towards the where shape from motion

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The transition to spatial vision parietal lobe

• Parietal lobe disorders
• Neglect syndromes body and space
• Working memory sustained where processing
• Apraxic disorders
• constructional apraxias
• ideational
• Sequencing deficits

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Fields vs. neglect?
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Laterality and visual deficits

• Spatial frequency
• Gestalt vs detail processing
• Tests that emphasize lateralized visual
  differences

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Body Dysmorphic Disorder- J. Feusner
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Sequencing deficits

• Numbers- digit span
• In speech literal paraphasias, neologistic
  paraphasis
• rhinosaur
• spelling