9/13 VisualSystem2 - Woodbury

Question 1

retinotopic map of calcarine fissure

blood supply

Answer 1

upper bank: upper retina: inferior eye field

lower bank: lower retina: superior eye field

occipital pole area: fovea

blood supply:

• medial portion perfused by PCA (post cerebral a)
• occipital pole CAN receive blood from MCA → spared in PCA infarct!
  
  • “macula sparing”

Question 2

V1

• prominent cortical layers
• organization

Answer 2

layers 4 and 6 very prominent (inputs from thalamus & outputs to thalamus)

contains columns with many functions

• eye-specific columns
• orientation columns

eye-specific layers in LGN map onto eye-specific columns in V1

Question 3

1M RGC → 1.5M LGN neurons → 200M V1 neurons

???

Answer 3

a lot going on in V1!

V1 starts to put info together

• seen in orientation columns
  
  • V1 simple cells respond only to line of light in single orientation in center of receptive field)
    
    • send out info to be analyzed into form/shape
  • V1 complex cells respond to lines of light in single orientation at multiple points in receptive field (earliest cells able to detect movement within receptive field via input from M cells)
    
    • send out info to distinguish movement

Question 4

what about areas outside of V1?

Answer 4

visual areas outside of V1 (V2, V3, V4, V5) demonstrate larger receptive fields aka visual association (secondary) cortex

• resp for creative attributes of vision
• specialized for diff aspects of vision (dominant fx, NOT exclusive fx!)
  
  • V2/V3 - form/shape
  • V4 - color
  • V5 - motion

*V5 further away from the others

Question 5

dorsal and ventral visual streams

Answer 5

dorsal: vision for action

• visuomotor area → helps you determine how you want to interact with something you see (objects, etc)

ventral: vision for identification

• “what is it?”

Question 6

visual cortex regions and lesions

Answer 6

V2/V3 apperceptive agnosia: visual acuity often intact BUT input cant be combined in a meaningful way

V4 achromatopsia

V5 akinetopsia: motion blindness

• static objects visible but disappear once start moving rapidly
• motion cna be detected in slow-moving obj, but direction of movement uncertain

Question 7

visual object recognition

compare to visuomotor impulses

implications

Answer 7

1. form a percept

• happens through cross-comm between V1/V2/V3/V4/V5 through ventral stream to come up with an integrated, unified percept
• happens above level of consciousness, BUT have to compare it with databack to id what the percept actually is

2. compare percept to database of known objects, look for a match

visuomotor: SEPARATE pathway for object interaction!

• dorsal stream
• splits off as early as V2
• never reaches level of consciousness UNTIL you approach object to interact with it!

implication: bc the two streams are separate, POSSIBLE to damage one and leave the other intact

Question 8

associative visual agnosia

Answer 8

ventral stream broken!

• can’t ID based on vision alone bc can’t compare percept to known objects
• can associate action with image seen via subconscious info in dorsal stream
• possibly reason out to an identification via motor movements

NOT the same as apperceptive agnosia!

Question 9

facial recognition

Thatcher effect

prosopagnosia

Answer 9

rapid eyes/mouth scanning

based on work with Margaret Thatcher’s photo - tells us that brain cannot process a face that’s upside down…but it thinks it can!

• more difficult to detect local feature changes in an upside down face

prosopagnosia: damage to temporal lobe, specifically affecting ability to recognize faces

Question 10

prosopagnosia details

cause

Answer 10

typically occurs after damage to fusiform gyrus, which has areas for…

• shapes
• faces (more R, fusiform face area)
• places (hippocampal place area)
• words (dominant)

prosopagnosia thought to require bilateral damage to FFA (fusiform face area)

• closed head trauma
• bilat stroke