control of movement trajectories Flashcards
what is the usual pattern of upper limb reaching mvmts
smooth
relatively straight
accurate
what do the speed and acceleration profiles look like in upper limb reaching mvmts
unimodal speed profile (bell curve)
biphasic acceleration profile
(* invariant across mvmt amplitudes *)
what do the stereotyped features of reaching movements suggest
the motor system explicitly plans and maintains the limbs trajectory
how much time is spent in acceleration and deceleration in healthy adults
45-50% acceleration
50-55% deceleration
(good marker for neuro disease)
how does hand speed change in aging and with damage to NS
increase mvmt time
increase relative time (higher %) spent in deceleration phase
- need more corrections
what is the traditional view of mvmt
that mvmt occurs in 3 distinct steps:
1. action selection
2. planning
3. execution
- involves selecting a specific hand trajectory to reach the spatial goal
- hand trajectory is an intermediate goal between spatial goal and motor command
what is action selection in traditional view of mvmt
selecting goal and determining features of goal (size, location, etc)
what is mvmt planning in traditional view of mvmt
selecting a specific hand trajectory to reach the goal
what is involved in inverse kinematics in the traditional view of mvmt
brain computes joints motion patterns to carry out desired hand trajectory
- how joints move to get there
(works bwd from the end position)
what do you need to know to do inverse kinematics
- start and end position of the hand
- difference in x and y of the start and end position
- initial joint angles
what is involved in inverse dynamics in the traditional view of mvmt
brain computes joint torque patterns to produce joint motion patterns
what do you need to know to do inverse dynamics
- the torques required to produce the joint motion pattern
- length of arm segments
- force of mvmt
what does the serial processing framework of the traditional view of mvmt imply
that the system explicitly computes and attempts to reinforce specific hand trajectories when moving to a spatial goal
T/F - there is invariance of hand paths across movement amplitudes, directions, speeds, etc
true
what is involved in the control of mvmt trajectory
- motor planning (select hand trajectory)
- desired joint angles
- motor execution
- desired joint torques
- movement
what is the evidence that trajectory matters
when arm is pushed closer to the target, hand returns to the original path due to brief reversal in elbow motion and finishes the task on the unperturbed path
what is deafferentation
cut dorsal roots
- no proprioceptive feedback
- leads to muted reflex responses
what behaviours were seen in learned tasks after deafferentation
- could still reach accurately to targets that it was trained to reach to
- if the elbow position was moved at all, the accuracy severely declines even with visual feedback
what are the goal directed feedback responses seen in timed single joint reaching task
time unconstrained = let the perturbation move them direcltly into the target (doesn’t return to original planned path)
time constrained = brief reversal in elbow motion to get there slower
what is shown in regards to trajectory control with goal directed feedback responses
- motor planning is goal dependent
- motor system can perform trajectory control when it’s the goal of the task
what is the difference between tracking a moving target vs a static goal when perturbed
moving - intercepts moving target after perturbation and continues to the goal
static - corrects directly to the static goal (skips rest of planned path)
when does the body correct back to the unperturbed trajectory (original)
when the trajectory is the goal of the task
what do both the goal directed feedback responses and tracking moving vs static responses show
trajectory planning is not a default property of the motor system
is there a difference in reaching mvmts between being shown a path and not shown a path
no - appear similar
