
Psychomotor skill and controls 263
The Lyapunov structure was also useful for developing the first math-
ematical model for the grasp phase of movement. When the arm extends
toward an object, there is a critical point located at approximately two-
thirds of the path toward the object when the hand opens up. The goal
of the model is to predict the critical point in order to send a signal to the
patient’s nervous system if the hand is not opening properly:
g
2
= a exp(bg
1
) + c exp(dx
1
), (8.13)
where g is the aperture of the hand, x is the position along the x axis, and a,
b, c, and d are nonlinear regression weights (Guastello et al., 2009, p. ...