·      Speed is determined by the performer (versus skills where the speed is determined by the skill itself, ie: throwing a baseball, typing, etc.)

·      A trade-off the emphasizes speed negatively impacts accuracy and vice versa

·      Fast and accurate movement or accurate movement at an unspecified speed

·      Ex: a soccer player making a penalty kick; need to sacrifice accuracy for speed, or vice versa

·      Predicts movement time for aiming movement (that requires both speed and accuracy)

Index of dificulty 

MT = a+b log₂(2D/W)

MT = Movement Time

A & B = Constants

D = Distance Moved

W = Target Width 

Log₂(2D/W) = Index of Difficulty

| Log₂ (2D/W) = X | D =32 W = 4 |

 Log₂ (16) = X

2^x = 16 | 2⁴ = 16 

Log₂ (16) = 4

2.     Closed-loop control process: feedback used

§  CNS needs to interpret this information to determine what modifications need to be made