Motor skill is easier to recognize than to define. Definitions
of skill such as: the “ability to achieve an environmental
goal with maximum certainty and minimal
expenditure of energy and time” (Schmidt and Lee,
2005) are not wrong, but suffer from a certain vagueness.
Here we will operationally define skill at the level
of motor execution, i.e., the ability to reliably deliver accurate
execution. A way to capture and quantify skill at
the level of motor execution is the speedaccuracy
tradeoff function, which refers to the relationship between
movement speed and accuracy for a particular
task. Subjects tend to make more errors as movement
speed increases and, conversely, to slow down in order
to be more accurate. Thus, an increase in accuracy alone
does not indicate improved skill; true skill acquisition
requires a systematic change in the learner’s
speedaccuracy tradeoff function (Reis et al., 2009;
Shmuelof et al., 2012). Unlike adaptation, which can occur
within a single experimental session, motor skill acquisition
can be achieved only through extended practice
and can take several days, weeks, or even years, depending
on the complexity of the task. Performance gains are
seen within-session (online effects) and between training
sessions (positive offline effects)