motor control Flashcards
what effect does increasing the reward associated with a target have on eye movement towards the target?
it increases the velocity of the eye movement
what effect does blinking have on eye movements?
it pushes the eye, altering its trajectory
what problems do increasing the velocity of eye movement and atltering trajectory cause for the occulomotor system?
motor commands that initiate eye movements are variable, due to variations in context and situation
the problem is how the occulomotor system is able to fixate on a target accurately despite this variation in initial state
what is corollary discharge and how does it deal with the problem of accurate fixation for the occulomotor system?
internal copy of an action command which predicts the sensory consequences of an action before sensory feedback is available
able to compensate for variability in the initial motor commands and produce accurate eye movements
what problem does delayed sensorimotor feedback cause for the motor system?
it can destabilise movements as results in continual over-adjustments whereby absense of feedback leads to additional movements
when the feedback arrives it shows the movement has gone too far so a big counter-adjustment is made
how might a forward model solve the problem of delayed sensorimotor feedback?
would generate a prediction of the position and velocity of a limb based on prior motor commands
enable feedback control to happen in real time and avoid instability associated with feedback delays
what additional advantage do forward models have?
can account for perturbations (disturbance of motion) affecting the directly perturbed muscle and other connecting muscles
can take into account the more physical dynamics of the limb
what evidence is there to suggest the cerebellum might generate forward models?
TMS to cerebellum disrupts ability to make accurate movements to a target that has disappeared
suggests cerebellum computes the likely position of the arm in the future and copensates by adjusting the trajectory
why would the oculomotor system have a better idea of teh position of the eye after an eye movement than before?
after making a movement the brain is able to combine 2 sources of info: prediction of sensory consequences of an eye movement (provided by forward model) and sensory feedback after completion of the movement
thus providing more precise estimate than if it had to rely on a single source of info
what is the role of the parietal cortex in identifying position of eye after eye movement?
neurons in parietal cortex remap their receptice fields before an eye movement occurs based on a prediction of the sensory consequences of the movement
neurons provide a model of what the woorld will look like after the eye movement
what would happen if we couldn’t predict the sensory consequences of making eye movements?
the brain wouldn’t have the ability to predict that the stationary image will move across the retina and adjust our perception in this way
world would appear to move and be blurred every time we move our eyes
what is the optimal way to combine 2 sources of info?
combine them in a way that minimises the variance of the resulting estimate
brain should incorporate a measure of uncertainty into its predictions
how should each source of info be ‘weighted’ when being combined?
info should be weighted in inverse proportion to the variance
so, weighting will be higher for source of info with lower variance and will be lower for source of info with higher variance
how does the brain form a ‘belief’ about the current state of the world?
by combining predictions about the sensory consequences of a movement with the actual measurements made at the time of movement
how might physical development of the body affect sensorimotor predictions?
it would change the relationship between motor commands and the actual motion of the limb
so affecting ability to predict the consequences of any particular motor command
