Speed Accuracy Trade Off

What is the speed accuracy trade off?

The more rapidly we move the more innaccurate we move

What is Fitts’ Law equation?

Movement time is plotted on a graph of = a + b [ log2 (2A/W)]

• log2 (2A/W) = the index of difficulty

• A = the distance from the targets

• W = the width of each target

• a = starting time (y-intercept)

• b = how much slower it gets as difficulty increases (gradient of line)

Why we are we less accurate when we speed up?

• Motor system noise is the natural variability or ‘random error‘ that occurs in the process of producing movement

• Fitts Law predicts that movements to small targets require more time because the effects of motor noise increase the chance of missing the target.

• Therefore to be accurate we must slow down

Why do quicker movements have more noise?

Quicker needed movements require a larger force to move faster, which increases the signal dependent force

What loop control is used for rapid movements?

Open loop

What loop control is used for slow movements?

Closed loop

What did the badminton study on SATO show?

• Players hit shuttlecock as fast as possible under two conditions: general direction (TB) or center target (CC).

• Key finding: Elite players perform best at 80–99% of max speed to maintain high spatial accuracy

What 3 groups were found from the badminton SATO study?

• Fitt’s inverse relationship group = high speed accuracy trade-off

• Low inverse relationship group = low speed accuracy trade-off

• No inverse relationship group = no speed accuracy trade-off

What is the evidence of SATO in throwing?

• In baseball and cricket players the most accurate throws were 70-85% of maximum speed

• In handball there was no trade-off

What is the cricket SATO study?

• 36 cricket players had to run out a batter as quickly, and as accurately as they could

• Accuracy condition = accuracy improved and more time was taken

• Speed condition = faster collection and approach to pick the ball, but speed of flight didn’t change

• 30% changed technique with instructions

What are the key findings from the coinciding time task?

• When movement time decreases, spatial accuracy decreases

• When movement time decreases, temporal errors decrease