control of movement trajectories

Question 1

what is the usual pattern of upper limb reaching mvmts

Answer 1

smooth
relatively straight
accurate

Question 2

what do the speed and acceleration profiles look like in upper limb reaching mvmts

Answer 2

unimodal speed profile (bell curve)
biphasic acceleration profile
(* invariant across mvmt amplitudes *)

Question 3

what do the stereotyped features of reaching movements suggest

Answer 3

the motor system explicitly plans and maintains the limbs trajectory

Question 4

how much time is spent in acceleration and deceleration in healthy adults

Answer 4

45-50% acceleration
50-55% deceleration
(good marker for neuro disease)

Question 5

how does hand speed change in aging and with damage to NS

Answer 5

increase mvmt time
increase relative time (higher %) spent in deceleration phase
- need more corrections

Question 6

what is the traditional view of mvmt

Answer 6

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

Question 7

what is action selection in traditional view of mvmt

Answer 7

selecting goal and determining features of goal (size, location, etc)

Question 8

what is mvmt planning in traditional view of mvmt

Answer 8

selecting a specific hand trajectory to reach the goal

Question 9

what is involved in inverse kinematics in the traditional view of mvmt

Answer 9

brain computes joints motion patterns to carry out desired hand trajectory
- how joints move to get there
(works bwd from the end position)

Question 10

what do you need to know to do inverse kinematics

Answer 10

• start and end position of the hand
• difference in x and y of the start and end position
• initial joint angles

Question 11

what is involved in inverse dynamics in the traditional view of mvmt

Answer 11

brain computes joint torque patterns to produce joint motion patterns

Question 12

what do you need to know to do inverse dynamics

Answer 12

• the torques required to produce the joint motion pattern
• length of arm segments
• force of mvmt

Question 13

what does the serial processing framework of the traditional view of mvmt imply

Answer 13

that the system explicitly computes and attempts to reinforce specific hand trajectories when moving to a spatial goal

Question 14

T/F - there is invariance of hand paths across movement amplitudes, directions, speeds, etc

Answer 14

true

Question 15

what is involved in the control of mvmt trajectory

Answer 15

1. motor planning (select hand trajectory)
2. desired joint angles
3. motor execution
4. desired joint torques
5. movement

Question 16

what is the evidence that trajectory matters

Answer 16

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

Question 17

what is deafferentation

Answer 17

cut dorsal roots
- no proprioceptive feedback
- leads to muted reflex responses

Question 18

what behaviours were seen in learned tasks after deafferentation

Answer 18

• 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

Question 19

what are the goal directed feedback responses seen in timed single joint reaching task

Answer 19

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

Question 20

what is shown in regards to trajectory control with goal directed feedback responses

Answer 20

• motor planning is goal dependent
• motor system can perform trajectory control when it’s the goal of the task

Question 21

what is the difference between tracking a moving target vs a static goal when perturbed

Answer 21

moving - intercepts moving target after perturbation and continues to the goal
static - corrects directly to the static goal (skips rest of planned path)

Question 22

when does the body correct back to the unperturbed trajectory (original)

Answer 22

when the trajectory is the goal of the task

Question 23

what do both the goal directed feedback responses and tracking moving vs static responses show

Answer 23

trajectory planning is not a default property of the motor system

Question 24

is there a difference in reaching mvmts between being shown a path and not shown a path

Answer 24

no - appear similar

Question 25

why is reaction time higher to plan curved mvmts compared to straight

Answer 25

no time cost required to plan straight mvmts
time cost required to plan curved mvmts
(unclear whether the lack of time cost in straight movements is because it’s the more commonly performed movement while curved movements are encountered less frequently)

Question 26

what does the higher reaction time for planning curved mvmts challenge

Answer 26

idea of trajectory control