Chapter 2. Prehension

182 THE PHASES OF PREHENSION
A
B
C
800 r
l2OI-
oL ' ' ' I
50 ' ' ' ' 100 '
Normalized time (%)
Figure 5.27 Kinematic profiles when grasping with pad
opposition using normal vision (NV) or with with vision
restricted to the central regions of the retina (CV) using specially
designed goggles. A. Resultant velocity profile of the wrist
marker B. Acceleration and C. Aperture beween the thumb and
index fingernail markers. Note that with only central vision, there
is absolutely no difference in aperture evolution compared to
normal vision. In contrast, with central vision only, subjects
seemed to underestimate the distance to the target (from Sivak,
1989; reprinted by permission from Sivak & MacKenzie, 1992).