“Two sides of the same coin”: constant motor learning speeds up, whereas variable motor learning stabilizes, speed–accuracy movements

Purpose The aim of this study was to determine the time course of the trade-off between speed and accuracy, intraindividual variability, and movement transfer and retention (4 weeks after learning) of speed–accuracy tasks. Methods The participants in this study were healthy adults randomly divided into three groups (control versus constant versus variable). They were aged 19–24 years, and 30 (15 men and 15 women) were in each group. Participants had to perform various tasks with the right dominant hand: (a) simple reaction test; (b) maximal velocity measurement; and (c) a speed–accuracy task. Results During constant and variable learning, the trade-off in a speed–accuracy task in specific situations shifted toward improved motor planning and motor execution speed, and to reduced intraindividual variability. However, during variable learning, the maximal velocity and variability of motor planning time did not change. Constant learning effectively transferred into variable tasks in terms of reaction time, average velocity and maximal velocity, and these effects were greater than those associated with variable learning. However, the effects of constant learning did not transfer fully into the performance variability of variable movements. Variable learning effectively transferred into constant tasks for the coefficient of variation of the path of movement, average velocity, maximal velocity and reaction time. The retention effect depended neither on learning nor task specificity (constant versus variable tasks). Conclusion Constant learning speeds up but does not stabilize speed–accuracy movements in variable tasks; whereas, variable learning stabilizes but does not speed up speed–accuracy movements in constant tasks.