Visual system


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Visual system

  1. 1. Neuropsychology of Visual Processes
  2. 2. General principles <ul><li>Various aspects of visual information are analyzed by different systems </li></ul><ul><li>Systems are distinguished at the structure/location and cellular levels, or both </li></ul>
  3. 3. Initial Visual Pathway <ul><li>Eyes </li></ul><ul><li>Optic Nerve </li></ul><ul><li>Optic Chiasm </li></ul><ul><li>Fiber crossover: separation of right and left visual fields instead of right and left eyes </li></ul>
  4. 4. Initial Visual Path Problems <ul><li>Retinal or other eye damage (e.g. macular degeneration, retinal stroke) </li></ul><ul><li>Monocular blindness; field cuts </li></ul><ul><li>Homonymous hemianopsias: bitemporal, nasal </li></ul><ul><li>Quadrantinopsias </li></ul><ul><li>Macular sparing </li></ul>
  5. 5. Middle Visual Path I: Geniculostriate Path <ul><li>Optic chiasm </li></ul><ul><li>Lateral geniculate body of thalamus </li></ul><ul><li>Optic radiations </li></ul><ul><li>Calcarine fissure: primary visual cortex </li></ul><ul><li>Purpose is pattern analysis and color perception </li></ul>
  6. 6. Middle Visual Path I: Thalamic Processing <ul><li>Two types of lateral geniculate cells </li></ul><ul><li>Magno cells--low specificity high rate (e.g. form & movement) </li></ul><ul><li>Parvo cells--high specificity low rate (e.g. color detection) </li></ul><ul><li>Some individuals with LD have abnormal frequency distributions of the two cell types </li></ul>
  7. 7. Middle Visual Path II: Tectopulvinar Path <ul><li>Optic chiasm </li></ul><ul><li>Superior colliculi </li></ul><ul><li>Thalamus </li></ul><ul><li>Occiptial lobe: secondary visual cortex </li></ul><ul><li>Purpose is detection/orientation to visual stimuli </li></ul>
  8. 8. Primary Visual Cortex <ul><li>Works on multiple represenation principle </li></ul><ul><li>Representations differ by </li></ul><ul><ul><li>Area </li></ul></ul><ul><ul><li>Complexity </li></ul></ul><ul><ul><li>Orientation </li></ul></ul><ul><ul><li>Color </li></ul></ul>
  9. 9. Visuospatial Disorders <ul><li>Main Types: </li></ul><ul><ul><li>Visuoperceptual disturbances: e.g. problems with visual identification </li></ul></ul><ul><ul><li>Visuospatial disturbances: more general than visuoperceptual problems </li></ul></ul><ul><ul><li>Visuomotor disturbances </li></ul></ul>
  10. 10. Visuoperceptual Problems <ul><li>Visual agnosias </li></ul><ul><li>Visual distortion </li></ul><ul><li>Visual confusion: figure-ground problems </li></ul><ul><li>Visual integration </li></ul>
  11. 11. Visual agnosias <ul><li>Problem with recognition (not naming) of visual stimuli </li></ul><ul><li>Special case: prosopagnosia--problems with facial recognition </li></ul><ul><ul><li>Unfamiliar faces </li></ul></ul><ul><ul><li>Familiar faces </li></ul></ul><ul><ul><li>Emotional expressions on faces </li></ul></ul><ul><li>Often due to R posterior brain damage </li></ul>
  12. 12. Visual agnosias (cont.) <ul><li>Tests to assess visual agnosias: </li></ul><ul><ul><li>Luria-Nebraska Neuropsychological Battery </li></ul></ul><ul><ul><li>Benton Facial Recognition Test </li></ul></ul><ul><li>In assessment, need to separate visual problems from naming problems </li></ul><ul><li>Separation done by double dissociation procedure: give two tests, one requiring recognition and naming, the other recognition only (in that order) </li></ul>
  13. 13. Visual distortion <ul><li>Figure recognized, but mental representation is distorted </li></ul><ul><li>Mild example: angulation problems, assessed by Benton Line Orientation Test (18/30 or below indicating problem) </li></ul><ul><li>Major example: form discrimination problems, assessed by Benton Visual Form Discrimination Test </li></ul><ul><li>Usually due to R posterior damage </li></ul>
  14. 14. Visual confusion <ul><li>Problems isolating specific visual percepts </li></ul><ul><li>Separation requires both visual and attentional abilities, also complex visual recognition </li></ul><ul><li>Usually caused by focal lesions to the brian, no specific area </li></ul><ul><li>Test: Poppelreuter Overlapping Figures Test </li></ul>
  15. 15. Visual integration <ul><li>Problem with integrating visual information into a meaningful whole </li></ul><ul><li>Generally caused by focal lesions </li></ul><ul><ul><li>Most common area R posterior, especially R posterior temporal </li></ul></ul><ul><ul><li>When one part of visual stimulus is intepreted as the whole, can be due to R frontal problems </li></ul></ul><ul><li>Test: Hooper Visual Organization Test (> 10 errors indicates severe problem) </li></ul>
  16. 16. Visuospatial Disturbances <ul><li>General problems that can have an overall effect on visual perception </li></ul><ul><li>Example: unilateral visual neglect </li></ul>
  17. 17. Unilateral Visual Neglect <ul><li>Primarily an attentional problem </li></ul><ul><li>Attention has three aspects: </li></ul><ul><ul><li>General awareness, level of consciousness </li></ul></ul><ul><ul><li>Nonvolitional/automatic vs volitional </li></ul></ul><ul><ul><li>General vs modality-specific </li></ul></ul><ul><li>Neglect is nonvolitional, modality specific </li></ul>
  18. 18. Unilateral Visual Neglect (cont.) <ul><li>Locations that can cause: </li></ul><ul><ul><li>inferior parietal lobule (right) </li></ul></ul><ul><ul><li>dorsolateral frontal lobe </li></ul></ul><ul><ul><li>cingulate gyrus </li></ul></ul><ul><ul><li>neostriatum (caudate, putamen) </li></ul></ul><ul><ul><li>thalamus </li></ul></ul><ul><li>Test: Line Bisection Test </li></ul>