-
What helps object recognition?
Motion
-
Where does motion processing occur?
Visual area MT
-
What can localize MT as a motion processing center?
An fMRI
-
What can probe motion processing in MT?
Random moving dot stimuli
-
What are MT neurons hightly sensitive to?
Motion coherence
-
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?
Optic flow
-
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?
- Where
- 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?
- What
- 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?
Inferotemporal cortex
-
What kind of neurons does the IT consist of?
Face-selective neurons
-
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
|
|