Problem 1 Flashcards
Extrastirate cortex is composed of … ?
2 segregated but interacting parallel processing streams
MT
Specialized for processing motion + depth
Traditional view of the action pathways?
Comprised of
- dorsal (where/how pathway)
vs
- ventral (what pathway)
Dorsal stream
Mediates navigation + the visual control of skilled actions directed at objects in the visual world
Ventral stream
Transforms visual inputs into representations that embody the enduring characteristics of objects + their spatial relationships
Dorsal stream lesions affect … ?
… 1. smooth pursuit eye movements
- Acura of goal directed arm movements
- speed discriminations
- complex mtotion perception
- Accruate encoding of visual space
Theory of independent visual-motor channels
Hypothesizes that reach-to-grasp movements require independent coding of different object properties
e.g. location, size, orientation etc
What does the newer view on action pathways consist ?
Dorsal stream should be subdivided into 2 sub circuits
Multiple parallel parieto-premotor circuits
They refer to the parallel running dorsal and ventral subcircuits/pathways in the dorsal system
–> dorso-dorsal + ventro-dorsal pathway
AND: maintain segregation until frontal cortex
What is the function of the dorso-dorsal pathway ?
Grasp-system
Controlling ones actions while they are on-going (“online”)
–> e.g. grasping something based on current visual info
What is the function of the ventral-dorsal pathway ?
Use-system
- Space perception
- Maintaining knowledge of particular skilled actions
associated with familiar objects - Action understanding
- -> recognizing + understanding the actions that were made by other
The dorsal + ventral streams clearly make up 2 relatively separate circuits.
Does that mean that the anatomical segregation between the 2 is absolute ?
No.
There is clear evidence of cross-talk between the streams
–> most connections from the V stream reach the ventral part of the D stream
THUS: VD stream constitutes an interface btw the ventral + dorsal streams of visual info processing
How do the sub streams thus interact ?
They both process the same set of visual attributes but for different behavioral goals
–> everyday actions require precise coordination between the systems
Lesions to the dorso-dorsal stream lead to … ?
Optic ataxia, where patients lose the ability to complete visually guided reaching tasks
–> reaching + grasping a target object with your hand arm/targeted arm movement
Lesions to the ventro-dorsal stream lead to … ?
Ideomotor/Limb Apraxia
- Deficits in object -related actions, meaning difficulty performing a motor task
- Especially without direct visual control, despite intact sensory, motor + language functions
The left lateralized system is crucial in making … ?
… correct inferences about the function of an object from its structure
–> tool use - knowing a calculator can do maths
Bilateral system
Specialized for online actions directed at currently visible stimuli on the basis of their structure
–> primarily subserved by a dorso-dorsal system
Left-lateralized system
Devoted to skilled, functional object-related actions
–> mediated by inferior venture-dorsal stream
e.g. tool use
Respondent behavior
Responding to an external stimulus
e.g. food is presented, eat it
Operant behavior
Operating on the environment by being or not being rewarded
e.g. dog coming up voluntarily - then getting a scratch on the back
Difference between respondent vs operant behavior ?
Respondent
–> externally triggered behavior
Operant
–> self-initiated behavior
How does operant behavior (self-initiated) show on a neuronal level ?
Neurons in
- Supplementary motor cortex (SMA + pre SMA)
- Lateral pre motor cortex
–> most crucial + firing in SMA, CMA - lateral does not have a big effect
It has been established that the same areas become activated when movement is externally triggered as when self-initiated.
How come ?
Activation in these areas are not confined to self initiated movements
BUT: activation in the pre SMA + SMA starts earlier when the movements is operant (
The role of the ACC in behavioral responding ?
It has cells that fire when an action is NOT followed by the expected reward
–> so an alternative action must be performed on the next trial
BUT: do not fire if there is an external cure that specifies the shift in responding
Function of the paracingulate cortex
Evaluation of ones own performance
Function of the medial frontal cortex/surface ?
Integrating info about our actions + internal state
- Self generated voluntary behavior
- Monitoring ones own performance
–> meaning the association of goals with actions, actions with outcomes
Object affordances
Involves reacting to changing situations in our dynamic environment
–> most linked to grasp system
Object affordances are important for 2 reasons.
Name them.
- Demonstrates the close connection between perception and action
- Provides an understanding of the importance of variability and context
Lesion to supplementary eye field (SEF) will lead to … ?
Deficits in voluntary eye movement control
Lesions to pre-SMA + SMA will lead to … ?
Deficitis in self-initiation oof movement
BUT: not when guided by sensory cues
When do unwanted movement plans occur ?
Established condition-action associations may cause automatic subconscious motor activation
–> even if the individual does not want to move in that particular way
AND: activations occur in SMA
What is the goal of the SUMNER study
Determining whether SMA + SEF contribute to voluntary control though automatic inhibition of unwanted motor plans
–> these are activated unconsciously by established condition-action associations
Masked prime task
- Participnts repsond to stimuli associated to left or right responses
- Stimuli are preceded by primes which are tended invisible by backward mask
Facilitatory priming
Masked prime task
Responding goes faster when the prime + target indicate the same response
Negative compatibility effect - NCE
Maske prime task
Slower responding for compatible trails
–> since an automatic inhibitory mechanism surpasses the motor activation evoked by the prime
Lesion to the medial PFC will lead to … ?
Alien hand syndrome that causes one hand to act on its own free will
–> the hand isn’t under the control of the mind and moves as though it has its own mind
4 steps of Motor planning
- Brain perceiving surrounding environment
- Identifikation of the object
- Determining required response action
- Issuing of a motor command
Motor planning
Refer to any processes related to preparation of movement that occurs during RT prior to movement onset
Lateral intraparietal area
LIP
Contains salience map for spatial attention
–> reflects the location of visual target rather than saccade endpoint
Default mode network
Is active when one is not engaged in a task
–> needs t be suppresses in order to attend to something + engage in a task
Stable affordances
Things that don’t change
–> cup size or color
