Is fitts' law continuous in discrete aiming?

  • Sleimen-Malkoun Rita
  • Temprado Jean Jacques
  • Huys Raoul
  • Jirsa Viktor
  • Berton Eric

  • Musculoskeletal system
  • Kinematics
  • Dynamical systems
  • Deceleration
  • Acceleration
  • Linear regression analysis
  • Principal component analysis
  • Velocity


The lawful continuous linear relation between movement time and task difficulty (i.e., index of difficulty; ID) in a goal-directed rapid aiming task (Fitts' law) has been recently challenged in reciprocal performance. Specifically, a discontinuity was observed at critical ID and was attributed to a transition between two distinct dynamic regimes that occurs with increasing difficulty. In the present paper, we show that such a discontinuity is also present in discrete aiming when ID is manipulated via target width (experiment 1) but not via target distance (experiment 2). Fitts' law's discontinuity appears, therefore, to be a suitable indicator of the underlying functional adaptations of the neuro-muscular-skeletal system to task properties/requirements, independently of reciprocal or discrete nature of the task. These findings open new perspectives to the study of dynamic regimes involved in discrete aiming and sensori-motor mechanisms underlying the speed-accuracy trade-off.