"Average movement time can be predicted as linear regression to the index of difficulty."

"The difficulty of selecting a target is proportional to its distance and inversely proportional to its width (index of difficulty)."

"If the user tries to increase speed, accuracy will be compromised, and vice versa: An increase in accuracy reduces speed."

“Attempts at reaching a target are limited by the speed and variance (accuracy) of themovement involved.”

“Human motor system is a limited capacity information channel.”