Principles of Speed Accuracy and Coordination

Question 1

What is the speed accuracy trade off?

Answer 1

If you perform the same action more quickly it will be done with less accuarcy

Question 2

What is Fitt’s Law?

Answer 2

Accuracy held constant
Independent variables: amplitude(A) and width (W)
Dependent variables: movement time (MT)
MT ~ A/W
Large amplitude movements to wide targets take the same time as small amplitude movements to narrow targets
Extended to discrete movements (not just tapping desk)

Question 3

What happens for rapid, discrete, open loop movements with no time for feedback?
(The Linear speed-accuracy trade off)

Answer 3

Independent variables: MT and A
Dependent variables: We= effective target width
Two main effects:
1) For a given rapid MT, as A increases, We increases
2) As MT decreases, We increases
Variablity~Velocity
=We~ A/MT

Question 4

Relationship of Fitts Law and The Linear speed-accuracy trade off

Answer 4

Not identical but both open and closed control systems show speed accuracy trade off

Question 5

What are sources of error in very rapid movements?

Answer 5

Every connection is an analog process, susceptible to transient factors
Each connection can introduce error and in general, when we produce more force we introduce more noise

Question 6

Given that more force = more variability and that noise in any muscle response can affect the resultant force, how does this explain open loop speed accuracy trade off?

Answer 6

When i am faster-> more force-> more variability

Question 7

What are the exceptions to the speed accuracy trade off?

Answer 7

Max force
Movements at ~ 70% of mac force become less variable
(more accurate closer to 100% max force)
Movement timing
-spatial accuracy
-timing accuracy

Question 8

What is spatial accuracy?

Answer 8

Accuracy of rapid movement for which the spatial position of the movement’s endpoint is important to task performance

Question 9

What is timing accuracy?

Answer 9

accuracy of rapid movements for which the accuracy of the movement time is important to task performance

Question 10

What happens opposite of spatial accuracy?

Answer 10

Timing accuracy gets better with faster movements

Question 11

What is bimanual skill?

Answer 11

Skill requiring the control and coordination of the two hands

Question 12

What is bimanual coordination according to bimanual fitts task?

Answer 12

Left slow and right hand slow (left target is far and target is close)
Actual results: left slow and right slower than expected

Movement of the right limb affected by task demands of the left limb
Suggests the two limbs are coordinated, perhaps by a joint motor command/program

Question 13

What happens during bimanual coordination with obstacles?

Answer 13

The thought is that hands are independent
Movement of the right limb is actually affected by task demands of the left limb
Additional evidence for single or coordination motor plan

Question 14

What do the unimanual results tell us during the gamma-v experiment?

Answer 14

That you can form a motor program for each independently

Question 15

What do the bimanual results tell us during the gamma-v experiment?

Answer 15

That the two motor programs cannot be run without significant interference. More evidence fro single motor program limit

Question 16

What is bimanual coordination during continuous timing?

Answer 16

Research shows that in-phase and anti-phase bimanual movements are motor stable than out-of-phase
Have similar timing structure/rhythm- simplifies the joint motor program
Research also shows that in phase is more stable than antiphase
Having preferred coordinated movement suggests another way the motor system solves the speed accuracy trade off
When one movement had too much speed demand = produce too much error, we can switch to another coordinated movement

Question 17

What does switching movements due to error suggest?

Answer 17

Suggests that there are degrees of freedom available to multi-limb coordinated movements is actually an advantage - can converge on more stable movement patterns each best suited to a specific speed

Question 18

What is the summary of Speed accuracy and coordination?

Answer 18

1) Fitts law: general finding that MT slows as ID goes up
2) linear speed-accuracy trade off: for very rapid movement error increase with shorter MT and larger increase
3) Coordination stability: when one pattern of movements becomes unstable due to speed, can switch to a more stable one