Chapter 2. Prehension

Chapter 3 - Serial Order in Prehension 61
would be accompanied by sensory, motor and sensorimotor
evidence.
4) Context: Memory of past experiences implies a central repre-
sentation, opposing the notion of purely dynamical reasons for
movement. This implies the presence of memory buffers that
could be affected by previous phases or previous conditions,
such as stability of grasp which is an underlying goal of pre-
hensile movement. With this view of memory, the motor system
is neither a slave to the dynamics, nor a slave to cognition.
5) Neural events: Underlying neural events include response
characteristics of various neural substrates. If neurophysiolog-
ical and neuropsychological evidence indicates that certain brain
areas are active or crucial at a given time and not at other times,
then this is converging evidence for a different phase of the
movement.
In contrast to a reductionist approach, the focus here is on senso-
rimotor integration processes, which are more than the simple sum of
the motor and the sensory components. Our goal is to present a holis-
tic approach, based on perception-based action and action-based per-
ception, achieved through multiple levels of sensorimotor integration.
The prototypical task introduced at the beginning of the chapter is
now more formally described. A subject sits at a table, with a hammer
on the table directly in front of her midline. The heel of her hand is
resting on the table and her forearm in semi-pronation. Her eyes are
closed, until a signal is given. She is told that she will grasp the object
to place it on the shelf. On the signal, she opens her eyes and per-
forms the task. Such a task requires the coordinated activity of almost
the entire body: trunk, eyes, head, neck, arms and hands. The task
requires the serial unfolding of a number of unique phases. Prior to
movement, there must be some planning. Movement begins and the
anticipatory shaping of the fingers is seen, appropriate for the task at
hand, as the limb moves. Then, the fingers begin to enclose around
the hammer. After initial contact, the hand captures the object, estab-
lishing a stable grasp. The object is then lifted and transported to a lo-
cation above the shelf. The hammer is then placed on the shelf, and
released by the hand.
For the remaining chapters of Part 11, we now turn to a more de-
tailed consideration of the serial unfolding of prehensile activity.