09-10. extrastriate processing Flashcards
2 main extrastriate pathways?
- dorsal (dorsal fin –> dory –> top)
- ventral
What does the dorsal pathway connect?
(LGN layer, pathway, cortex)
- MAGNO cellular layer
- MT (middle-temporal visual area)
- Parietal cortex
What is the dorsal pathway most important for?
“where” / “how” pathway
(dOrsal = hOw)
What is MT important for?
Motion perception!
Specifically direction, more than just flickering
MT = MoTion
What does the ventral pathway connect?
(LGN layer, pathway, cortex)
- PARVO cellular layer
- V4
- Inferotemporal cortex
What is the ventral pathway most important for?
“what” pathway
venTral = whaT
What is V4 important for?
- form
- color
V4 –> “FOURm” & color
How is V4 sensitive to form and curved edges?
- V1 cells have preferred orientations that indicate short, straight edges
–> V1 tells us BARS - V4 cells combine info from V1 cells to add bars and make a CURVED edge
- curved edges important for perceiving CONTOUR / form
How does the IT cortex perceive form?
- V1 = straight
- V4 = curves, contours
- IT cortex = SHAPES
- cells in IT cortex respond to combinations of contours, with relatively large receptive fields
What experiment is the PARIETAL cortex crucial for?
- landmark / “where” task
- monkey learns that food is in the bin with the object near it
- with damage to PARIETAL cortex…
–> they have trouble identifying WHERE food is
–> struggle with SPATIAL LOCATION
What experiment is the IT cortex crucial for?
- object / “what” task
- has to differentiate between a square/triangle or between red/green to get food
- with damage to IT cortex…
–> struggle with FORM and COLOR
What happened with the patient with ventral stream damage? What could/couldn’t she do? What does this tell us?
- couldn’t identify objects, but could draw pictures from memory
- couldn’t report orientation of slot, but could insert a card into it
- affected VERBAL report, NOT her ACTION
- ventral / IT is essential for identifying objects
- there might be information that a person doesn’t have conscious access to
–> may be in the dorsal / MT pathway
–> she was able to complete motion/action, but not perception
Dissociating perception and action meaning…?
Idea that perception and action happen in different visual pathways
Ventral –> Perception (end of alph.)
Dorsal –> Action (beg. of alph)
How to study dissociation in non neurologically compromised people?
Compare the effects of an illusion on…
1. judgement on appearance of stimulus (perception)
2. motor actions towards it
–> like picking it up
ex.
- small stick that looks bigger (like railroad track illusion lines)
- dots surrounded by other dots
- motor action is the same for the same physical stimulus, regardless of perception
What is modularity?
Very specialized processing locations for different visual / brain functions
