A ball throwing task example (John &
Cusumano, 2007). (A) Schematic representation of the
task, the goal of which is to hit the target; the body state is x =
(θ,ω), so Db = 2,
and the goal-level error is e, so
Dg = 1. (B) A typical GEM for the
task (gray line), and ±10% error contours (black lines) in the execution
variable space. The GEM is the set 𝒢 containing all values of x that
satisfy Eq. (2), giving
trajectories that exactly hit the target. Angular variables are displayed in
radians. The circle is for later comparison with Fig. 3.