speed accuracy trade off
when trying to perform a skill quickly, we end up making more mistakes
-ex: athletes performing open skills - have to make shots quickly and accurately
fitts’ law
what is Fitts’ law’s equation
MT = a + bLog2(2A/W)
which two things do we need to know in order to predict movement time using Fitts’ law?
amplitude moved and target width
which part of Fitts’ law equation represents the index of difficulty? (ID)
Log2(2A/W)
Woodworth’s two component model
how does the speed accuracy trade off relate to open and closed loop control (our model)?
when we move quickly, more mistakes are made in the RESPONSE PROGRAMMING PHASE, need more corrections
-when we want to do something carefully, often take more time to complete the movement
what are 4 things that Fitts’ law tells us?
1) MT increases as the distance increases
2) MT increases as the size of the target decreases
3) MT is constant for a given ID
4) Fitts’ law only applies when we are doing things as quickly and accurately as possible
what are the 2 violations of Fitts’ law?
1) effective target width
2) dependent on the visual context being presented
- when movement amplitude doesn’t necessarily mean increased MT: MT is less when aiming at the last target in a row of targets (choice reaction time task) as opposed to the second last for example
violation of Fitts’ law: effective target width
linear speed accuracy trade off describes which law?
more force results in more variability in our movement
which stage of programming is affected by the sources of error in rapid movements?
at what percentage of force are we most variable in our movements?
what are two exceptions to the speed accuracy trade off?
1) extremely rapid and forceful movements
- longer movement times, more time for closed loop control
- move really fast, see a decrease in variability
2) timing accuracy is critical to the action
- with more time, comes more timing error
- ex: counting to 10, you’ll have less error than when counting to 20
which 5 factors play a role in analyzing rapid movement (ex: hitting a base ball)?
1) visual processing
- able to more accurately predict where the ball will be at impact
2) swing initiation timing accuracy
- decision made closer to ball contact - less time for error
3) movement timing accuracy
- MT is more consistent - better chance of hitting the ball
4) movement spatial accuracy
- relates to force variability curve
5) ball impact
- physics - hitting harder will make the ball go further
prehension - def
the action of reaching for and grasping an object that is stationary or moving
how does prehension relate to Fitts’ law?
as we grasp for an object, we initially reach quickly but decelerate once we get closer because we need to be more precise with our movement
how does bimanual coordination relate to Fitts’ law?
when performing bimanual movements, the target that is more difficult will be the rate limiting factor in the movement; the limb with the easier target will not move faster
what stage of programming is affected in bimanual coordination tasks?
response programming
-one motor program is being sent to both limbs even though they are supposed to perform different movements
symmetric bimanual coordination
-preferred pattern of movement
1) anti-phase: alternating movements
2) in-phase: homologous muscle for movements on both sides
how can you measure relative phase in bimanual coordination?
asymmetric bimanual coordination
- ex: skilled drummers
what are two possible explanations of bimanual coordination?
1) generalized motor program
- develop 1 or 2 new programs?
- with practice, able to merge more than one program together
2) dynamical systems
- new attractor state ‘emerges’
- in phase and anti phase
- with practice, SD (variability) goes down, becomes a stable pattern
what are two possible explanations that explain the speed accuracy trade off?
1) motor program
- movement longer (reduced speed)
- accuracy decreases (variability increases)
2) dynamical systems
- if variability increase; seek new coordination pattern
- as you move faster, relative joint positions become more variable, you seek a new coordination pattern that takes longer to perform