Lecture 19 - Tradeoff between the speed and accuracy of voluntary motor actions Flashcards
What is the speed-accuracy tradeoff?
In general, we can move quickly at the cost of accuracy or accurately at the cost of speed
High speed - low accuracy
low speed - high accuracy
What factors influence the spatial accuracy of movement?
- motor variability scales with movement speed
- Fitts theorem
- Neurophysiological principles governing movement variability
Does error increase or decrease as speed increases?
error increases
What happens to the dispersion of end points when movement speed increases?
it increases
What does Fitts’ theorem describe?
The relation between movement amplitude, accuracy and movement time
What is the formula for Fitts theorem?
MT = a{log(base 2)[2A/W]} + b
A: movement amplitude
W: target width
Index of difficulty: (log(base 2)(2A/W))
Fitts theorem
What happens to MT when amplitude increase?
Movement time increases
Fitts theorem
What happens to MT when target width increases?
Movement time decreases
Fitts theorem
What factors affect index of difficulty?
Movement amplitude
target width
Low speed, ____ index of difficult
High or low
high
high speed, ____ index of difficult
High or low
low
What would be an example of something with a high ID? Low ID?
ID - index of difficulty
High - performing surgery
low - open net in soccer
When is movement time constant?
For a fixed ratio of movement amplitude to target width
Speed-accuracy tadeoff graph
Why do older adults have a higher intercept?
baseline movements (unconstrained) are slower
Speed-accuracy tadeoff graph
Why do older adults have a higher slope?
Speed-accuracy tradeoff is more severe
What are some examples of Fitts’ theorem in daily life?
- keys on a keybord that are frequently used are larger (like the space bar)
- golf: driver is longer increaseing ball speed, but reduces accuracy, pitching wedge is shorter, decreasing ball speed but increases accuracy
What is motor variability proportional to?
amount of force produced
As muscle force increases does error increase or decrease?
Increase (more variability)
What % does force variability peak at?
75% MVC
Are faster movements more or less variable?
More variable, require more force
Which type of muscle fibres (slow or fast twitch) have smaller innervation #s?
Slow
Which type of muscle fibres (slow or fast twitch) tend to contribute to larger motor units?
Fast twitch
What happens to the variability of muscle force production when larger motor units are recruited?
We see more variability during voluntary contractions
When movement times are constrained, the dispersion of movement endpoints is directly proportional to what?
movement speed
