Chapter 2. Prehension

Chapter 7 - Opposition Space Phases 291
locked, they are spatially and functionally coupled. The Drive Fingers
Guarded Schema in Figure 7.4 is controlling the final positioning of
the grasping surface patches of the hand, through proximal and distal
muscles. That is, the model suggests that there are not separable
transport and grasp components in the final approach to the object. All
control is directed to alignment and the placement of the grasping
surface patches on the hand with respect to the palm and object.
Activation of
Reaching
' reaching and grasping Object properties
I Task requirements
c - - - - - - - - - - - - - - - I
1 !
I
I
*
I
I
I
I
1
I
+ r
Orient
Palm
Schema
I
J
Drive Fingers
Guarded
Schema
Preshape
Schema
Grasping
Figure 7.4 Palm-focused model of Setting Up Opposition Space
for prehension. During activation of the Orient Palm Schema,
reaching movements orient the palm and position it close to the
object. In parallel, the Preshape Schema shapes the fingers into a
posture suitable for that palm alignment. When preshaped, posi-
tioned, and oriented, the Drive Fingers Guarded Schema is
activated in order to drive the arm, wrist, and hand in a direction
to make contact with the object. Since it is a guarded move,
contact with the object will stop the schema, and activate the
Actual Grasp Schema.