Module 6 Flashcards
What does Fitts’ law mean?
Movement time is constant whenever the ratio of the movement amplitude to target width remains constant
Movement time increases as the ratio of A to W increases by making A larger, W smaller, or both
Example of Fitts’ law
Alternative tapping two targets that are A (target distance) apart and are W (target width).
There is a home position in the middle where the person starts.
The farther away they are (increased A), the slower the movement time will be.
The thinker the targets are (decreased W), the slower the movement time is with good accuracy (bad accuracy with static speed).
Linear Speed-Accuracy Trade-Off
Suggests that for various combinations of A and MT, that has a constant ratio (constant average velocity), the aiming errors are about the same
As movement velocity increases…
Errors increase linearly
How to maintain movement accuracy in rapid tasks?
Trading off with increases in movement distance and decreases in movement time
Why does increasing the speed of rapid movement lead to inaccuracy?
The contraction forces of the various muscles being used determine the the resulting trajectory of the moving limb
When does inconsistency in forces increase?
When the forces increase
Inconsistencies
Noise
Variability
Example of inconsistencies
Record players are preprogrammed with music but many things (scratching, warping) can affect its ability to play that music
When is more force required?
When the movement time decreases
When the amplitude increases
What does more force lead to?
More variability because it causes the movement to deviate from the intended trajectory that leads to more inaccuracy
What happens when a movement requires very high levels of muscular contractions?
Increased speed by reducing movement time can decrease spatial and timing errors
When is one most accurate?
At low force (slow) and high force (fast)
Temporal time =
When
How does one make movements more temporally accurate?
Decreasing movement time (moving faster)
Bimanual Fitts’ Task
Both limbs could be assigned identical tasks with either low or high IDs or to different (incongruent) tasks
When is the explanatory power of Fitts’ Law reduced?
When separate and incongruent task demands are required of two limbs
Gamma-V Experiment
W separate motor programs
Can’t be run at the same time without considerable interference
What is similar to the gamma-v experiment?
Patting head/rubbing stomach
Continuous Bimanual Timing
Controlling the continuous movement of two limbs (each with its own spatial/temporal goal)
What can the executive do?
Use a common movement command to control the movements of both limbs
Switch attention rapidly between the executions of the two tasks
Why can the executive do those things?
The movements are ongoing
ID
Index of difficulty
Defines the difficulty of the various combinations of A and W
Speed-Accuracy Trade-Off
Tendency for people to “give up” speed in order to trade speed off for acceptable levels of accuracy
Why are slower movements more accurate?
There is more time to detect errors and to make corrections
When does movement time lengthen?
When the number of corrections to be made increases
When does the speed-accuracy trade-off usually occur and why?
Usually in slow, closed-loop actions bc one has to be able to make the corrections
What happens when performance accuracy (stability) is threatened by increased speed?
A motor system seeks a more stable coordination pattern to take its place
Doesn’t let accuracy keep diminishing with the increasing speed and the coordination changes so stability can be reestablished
What can the motor system do when increased speed leads to decreased accuracy? (3)
Reduce speed and maintain accuracy
Decrease accuracy and maintain speed
Maintain speed and change the movement pattern in order to reestablish stability
