Figure 5.

(A) The energy margin EM as a function of time (black line) in one early practice trial for one older subject. If EM > 0, the ball will never escape from the cup, if the current cup acceleration is maintained. However, if EM ≤ 0 the ball will escape from the cup, unless the cup acceleration is changed. For the latter case, the time-to-escape is shown (dashed red lines); for EM > 0 the time-to-escape is infinite (the ball will oscillate within the cup). (B) For the same trial, the three variables that determine EM, ball angle and angular velocity and cup acceleration, are shown in a three dimensional task execution space. The trial starts in the center (yellow triangle) and moves through the execution space as the trial progresses until the cup is stopped at the spatial target (yellow square). The blue mesh represents the critical EM level, i.e., where EM = 0. The colored circles provide timing landmarks every 0.25 s.