Ventral and Dorsal Stream Flashcards
What is the ventral stream vs. dorsal stream?
Ventral: info related to objects, temporal association cortex, uses shape/colour, touch/sound info to identify objects
semantic knowledge/memory about the world.
dorsal: info about spatial arrangments “where objects are”, pareital association cortex, visual and somatosensory info is used to understand spatial relationships and guide attention
How does the brain identify and understand objects?
Low level visual processing (detecting contrast, shape)
Intermediate level (detecting visual surfaces)
This info is integrated to make …
Higher level (semantic content)
1) categorial linking
2) image linking
3) associative learning
**
tied to emotional valence, sensory modalities, experiences have emotions attached to them. how are they integrated.
How are higher order representations made in the ventral stream by convergence?
Remember the “bar of light”, well now you have cells that fire in response to multiple light orientations (oreintation specific RFs for all possible combo of converging neurons)
Fragments of objects CONVERGED to get higher order represenation
i.e. making a triangle from 3 lines.
IT is highest order representation.
How do we infer function of the normal brain based on RF firing?
In studies with monkeys, you can use the inferotemporal cortex which responds to specific stimulus (i.e. faces)
FOUND: when stimulus (Face) is visible, there is more firing. when face is manipulated/disoridented, firing goes down.
What does prosopagnosia result in?
Damage to face selective regions of the temporal lobe. Fusiform gyrus (important for perceiving faces)
How is the temporal cortex organized?
In columns. with large receptive fields.
RF in V1: 1 degree
RF in V4: 10 degrees
RF in inferotemporal: up to 100 degrees.
Hypercolumns (cluster that represent a class of stimuli)
Perceptual constancy (ability to recognize an object despite variations like size, colour, position etc.) - population of coding of viewpoint neurons OR convergence in higher visual regions.
THis has been shown in cylindrical objects shown to primates.
What is the Jennifer Aniston neuron?
Neuron that fires specifically to pictures (many) of jennifer aniston. All images elicted firing in response to jennifer aniston, you can conclude its specfically for her, even fired to the written word of her name.
At the highest level of heirarchy, single neurons represent each individual items in our perceptual experience/memory.
- maybe but its impractical
neuron also fired to Lisa Kudrow, so items are unlikely to be represented by invidual neurons, but by POPULATIONS and population codes.
How does associateive learning allow neuronal representations to be linked?
THe medial temporal lobe links neocortical representations.
i.e. How a horse stimulus may effect a circus tent.
Low/intermeidate level visual processing goes to medial temporal lobe to be consolidatied, then to inferior temporal cortex for memory storage, then to prefrontal cortex (working memory)
Associative learning allows both to fire to one stimulus. you “associate” them with each other.
What is the two stage model of object recognition?
- Apperceptive Agnosia (damage to posterior IT)
- can identify verbally but cannot draw/construct sensory representations of visuals stim.
- cannot see object parts as a unified whole - Associate Agnosia (damage to anterior IT, higher up in associative heirarchy)
- cannot interpret or assign meanings to objects. Can copy images with detail but cannot speak what they have drawn.
Sensory representation okay but not associated with meaning.
What are the two subdivisions of the dorsal stream?
Dorsal and Ventral.
Dorsal area: closer to somatosensory cortex, more motor functions related to space. Interacting appropriately with objects
Ventral area: closer to visual cortex, more pure spatial functions in perception and cognition. Perceiving space.
Convergence into higher order represenations, create spatial relationships.
What is spatial neglect and where is the damage?
Other types of damage?
Parietal association cortex (dorsal stream, ventral area)
(right cortex)
ignoring left part of the visual field.
Other posterior parietal damage can result in REPRESENTATIONAL neglect (recalled memories at the Duomo)
- memories can be represented according to one’s vantage point)
- **
and
MOTOR DEFICITS
- neglect of body parts, inability to reach for objects/orient the hand. (but no problem in the dark)
How does activity change when engaging with stimulus in posterior parietal neurons.
In dorsal stream, DORSAL AREA, when you aren’t attendint to object, you don’t get much firing. when you glance at the object, you get more firing and when you TOUCH the object you get the most firing.
Write out table on 1st lecture near the end
do itt
Where do dorsal and ventral streams converge on? Describe this region.
the hippocampus. The two distinct streams with highly processed info converge onto hippo to distinguish specific experiences from each other.
Object info (ventral) and spatial info (dorsal) converge to LEC and MEC RESPECTIVELY and then go to hippocampus.
LEC and MEC send inputs to dentate gyrus (densly packed with neurons) which goes to CA3, very interconnected. If you activate just a few, they will all be activated cause theyre all connected! (partial cue to retrieve full memory)
