Chapter 2. Prehension

130 THE PHASES OF PREHENSION
SR = .40 SR = .45
1
0.00 0.22 0.44 0.65 0.87 1.09
TIME
SR = .49
u
21 -2
0.OQ 0.08 0.16 0.23 0.31 0.39
TIME
a
-0
a
0.00 0.15 0.30 0.44 0.59 0.74
TIME
H
K
0
Z
NORMALIZED TIME
Figure 5.7 Velocity profiles from the VITE model. A. Velocity
profile of 20 unit distance movement with small GO signal. B.
Velocity profile of 20 unit distance movement with medium GO
signal. C. Velocity profile of 20 unit distance movement with
large GO signal. D. Superimposing velocity profiles from A, B,
and C. Note slower movements have an aymrnetrical velocity
profile. SR=time taken to move half the distance divided by total
movement time (from Bullock and Grossberg, 1989; reprinted by
permission).
portional to a function of movement amplitude and target width. The
coordination of all muscles involved in a multi-joint movement reflects
a rather stereotyped behaviour, with coupling synergy of the shoulder
and elbow during reaching. Plamondon (1992) provides a sequential
generation model to explain the origin of asymmetric bell-shaped ve-
locity profiles and to describe them with a log-normal function.
Neural simulations that produce symmetric and asymmetric velocity
(D)