Chapter 2. Prehension

110 THE PHASES OF PREHENSION
anticipated, and there is continued orientation and positional
adjustment until the hand grasping surfaces make contact on specific
locations, given the opposition(s) used.
5.1 Overview of Trajectory Planning
Arbib’s (1985) coordinated control program (CCP) was presented
in Chapter 3 as a conceptual model that addressed how the arm and
hand might be controlled during reaching and grasping. In Figure
5.1, the lower section of the coordinated control program has been
extracted in order to focus on the motor aspects of the program.
activation
of reaching
I BALLISTIC
and
input
Figure 5.1 The motor aspects of the coordinated control program.
On the left, the two phases of the reaching component are seen.
On the right, the grasping component involves the adjustment of
the fingers into a suitable shape, rotation of the wrist, and then
the actual grasp on contact (from Arbib, 1985; adapted by
permission).
In this chapter, trajectory planning is analyzed for the arm (left side
of Figure 5.1) and the hand (right side of Figure 5.1), paying careful
attention to the control mechanisms, the computations that have to be
performed to support these control mechanisms, and the temporal,
spatial, and functional relationships between these schemas. The pro-
cess of transporting a hand to a location (or for that matter, opening
and closing the fingers) can be thought of as 9ndDoint trajectorv rren-
eration, and it entails an analysis at various levels of motor control.
This issue is studied at levels that include joint angles, joint torques,