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What helps object recognition?
Where does motion processing occur?
Visual area MT
What can localize MT as a motion processing center?
What can probe motion processing in MT?
Random moving dot stimuli
What are MT neurons hightly sensitive to?
What is optic flow?
- Motion that arises b/c of your own motion
- You're moving thru space
What's an example of self-generated motion?
What is visual area MT?
- Middle temporal area
- Downstream from visual cortex
- Comparatively small compared to rest of brain
What parts of the brain are in the temporal lobe?
What's the difference between detecting motion and simply detecting change in contrast by flipping between black and white?
- Both stimulate the visual cortex of brain
- But motion stimulates slightly downstream (MT)
What's the significance of motion coherence on responses of MT neurons?
- Degree of coherence determines which neurons fire
- Ex. A lot of firing when all objects going in preferred direction after a vote
What is the process involving monkeys and motion percepts?
Microstimulate at a site in MT where neurons prefer downward motion while monkeys make up/down motion judgments for stimuli with various levels of coherence
What kind of architecture does MT have?
Has vertical columns of neurons sensitive to different movement directions
What happens when you electrically stimulate columns in MT?
- Alter motion perception
- Make person/animal think object is going in a different direction
Describe the graph after microstimulation of MT
- Looks like a leftward shift of perception+confidence curve
- Generally at 0 coherence (random mvmt), normal animal can't tell direction
- But with stimulation, still knows/is confident of the right direction
How are higher visual functions separated?
- Dorsal Stream
- Ventral Stream
What kind of info is the dorsal stream in charge of?
- Doesn't care what object is
- Just where it is and where its going
What's the point of the dorsal stream?
Helps coordinate vision and motor activity
What kind of info is the ventral stream in charge of?
- Doesn't care where object is
- Just its color, form, etc.
Where does the dorsal stream project to?
Projects through the parietal lobe to represent location and motion
Where does the ventral stream project to?
Projects through the temporal lobe to represent form and object recognition
How are cortical visual areas connected?
Highly reciprocally connected
What kind of processing is required for visual perceptions?
Both hierarchical and feedback processing
What does IT stand for?
What kind of neurons does the IT consist of?
How are face-selective neurons arranged in IT?
In clusters in small selective-for-face regions
What's the point of the Jennifer Anniston study?
- Shows single neurons can be devoted to very very specific faces
- Invariant to orientation of face
- But context can change perception (+Brad)
How are representation of object classes also organized?
Into cortical columns
What happens when IT is damaged?
Impairs object recognition
What are the different kinds of object recognition impairments?
- Apperceptive agnosia
- Associative agnosia
Describe apperceptive agnosia
- Slightly more posterior
- Cannot see object parts as unified whole
- Unable to construct sensory representations of visual stimuli
- But can still verbally identify object
Describe associative agnosia
- Slightly more anterior
- Cannot interpret, understand, identify, or assign meaning to objects
- Sensory representation is created normally cannot be associated with meaning, function, or utility
- Reproduces object with no problem; Can't identify