Chapter 2. Prehension

Chapter 7 - Opposition Space Phases 299
1 1. Contour following is a ballpark of the actual opposition vector,
using task mechanics.
12. Controlled slipping is a ballpark (Johansson & Westling, 1984,
1987, 1990).
13. The coordinate frame for finger muscles is palm-centered in
using an opposition space.
14. The controller being used is feedback or feedforward.
15. If contact is not made with the object in a certain amount of
time, the controller for enclosing the fingers will signal other
schemas (Arbib et al., 1985).
16. Decreasing grip and load forces is a transition, anticipating
transfer of support to another surface.
17. Perturbations during the decrease in load and grip forces prior
to release will cause an increase in these forces, delaying the
release.
7.4 Releasing an Opposition Space
Once support for the object has been transferred to another support
surface, the opposition space can be released. The hand opens, re-
laxing usually into the position of rest, or position of function, where
the muscles and tendons are in an equilibrium position. The shoulder
and arm transport the hand away from the object.
From the experiments and computational models put forth in
Chapter 6, the underlying hypotheses are made explicit for the reader’s
further evaluation and research:
1. The hand drives the arm.
2. There are feedforward anticipatory mechanisms of control.
3. No vision is needed.
7.5 Summary of Opposition Space Phases
Prehension seems to involve a series of phases. ‘Triggering’ of
these phases seems critically dependent on making and breaking
contacts with the environment (contact between hand and object,
contact between hand plus object and supporting surfaces). Unique to
each phase are the motor characteristics, the influences of sensory
information, the intent or goal, the context within it is occurring, and
the corresponding neural events. The Planning Phase demonstrates
much brain activity in anticipation of the movement, drawing on
previous knowledge of objecthand interactions. Opposition vector(s)