Chapter 2. Prehension

Chapter 5 - Movement Before Contact 143
DURATION (ms)
Figure 5.14 Wrist velocity and aperture profiles for grasping a
large cylinder 5.5 cm in diameter, without vision of the object.
On the left, the velocity profile is shown as the subject reaches
out to grasp an object of constant size placed 25, 32 or 40 cm
away. On the right, no difference is seen in the pattern of
aperture between the thumb and index finger over the course of the
movements, among the distances evaluated (from Jeannerod, 1984;
reprinted by permission).
that the two types of properties are likely to be detected through differ-
ent structures or channels. Specifically, for grasping an object, sepa-
rate visuomotor channels are activated in parallel by a specific visual
input and controlling a specific part of the limb musculature. For ex-
ample, extrinsic spatial properties of an object activate proximal mus-
cles (e.g., about the shoulder joint) for the transport component, and
intrinsic object properties activate distal segments (e.g., wrist and fm-
gers) for the grasping component.
With respect to the coordination between reaching and grasping,
he found that in the descent period after peak velocity, a change in the
velocity was seen at around 7040% of the total movement, which cor-
egocentric spatial properties such as distance, orientation, direction and velocity of
object motion with respect to the body).