L11B: Principles of Speed & Accuracy Flashcards
What is Schmidt’s Law?
Linear Speed-Accuracy Tradeoff (Schmidt’s Law)
- Occurs in very fast discrete movements (< 300 ms), where there’s little time to process feedback (ballistic/open-loop).
- Accuracy changes as the duration and distance of the movement vary.
According to Schmidt’s Law,
How does accuracy affect speed?
- Schmidt’ law describes tradeoff between accuracy & speed
- Increase in speed → Worse accuracy (increased variability)
- Movement speed is varied and accuracy is measured
What is Effective Target Width?
Instructed to land as close as possible to spatial target under
different MT and amplitude goals (i.e., velocity* constraints).
What is measured is the ‘accuracy’ of the endpoints:
Effective target width (We)=SD in movement endpoints (VE)
Manipulating MT & Amplitude (velocity) results in linear
relationship with performance variability (accuracy)
What is the Equation for the Line?
A) the distance b/w 2 targets
C) the width of each target
D) Movement Time
(B)Increasing the distance between the targets
(B) The standard deviation of a participant’s endpoints in a rapid-discrete aiming task.
What are the Two speed-accuracy trade-offs that are
related yet account for different conditions?
What are the reasons for these
speed - accuracy trade-offs?
1) Logarithmic speed-accuracy trade-off
primarily related to FB (feedback) processing
2) Linear speed-accuracy trade-off related to force variability (fast - no time to use FB)
How does FB (feedback) processing lead to a speed - accuracy trade off?
- As precision demands increase, importance of vision/feedback increases to achieve accuracy
- If you slow your movements down, more able to make small corrections to the movements
- Movements are probably controlled using both OPEN and CLOSED-loop processes because there is time to use feedback
How does Force Variability lead to a speed - accuracy trade off?
- Very fast, temporally constrained movements. Errors related to “noise” in the programmed movement
- Movements are probably controlled
using only OPEN-loop processes -
Faster movements require more force,
which will lead to more variability
As force increases, how does
variability in force change?
As force increases, variability in forces also
increases (up to a point - ~70% of max)
How does endpoint position variability (We) behave with force/MT?
With the exception of very fast (nr max) forces endpoint
position variability (We) increases linearly with force/MT
In the slower Fitts’ type tasks, we optimize (balance)
size of initial forces & feedback corrections. How?
