Biomedical Engineering Reference
In-Depth Information
600
12
500
10
400
8
300
6
200
4
2
100
0
0
0.15
0.17
0.19
0.21
0.23
0.25
0.15
0.17
0.19
0.21
0.23
0.25
Time (s)
Time (s)
100000
0.9
0.8
80000
0.7
60000
0.6
40000
0.5
20000
0.4
0
0.3
-20000
0.2
-40000
0.1
-60000
0
0.15
0.17
0.19
0.21
0.23
0.25
0.15
0.17
0.19
0.21
0.23
0.25
Time (s)
Time (s)
FIGURE 13.43
Simulation for Example Problem 13.7, with
F
p
¼ 1.3 N,
t
1
¼
0.10 s, t
ac
¼
0.018 s, and
t
de
¼
0.018 s.
Many other parameter sets can also simulate a 10
saccade. For instance, consider reducing
t
de
to .009 s. Because the antagonist active-state tension activity goes toward zero more quickly
than in the last case, a greater total active-state tension (
F
ag
-
F
ant
) results. Therefore, to arrive
at 10
withtheappropriatemainsequencecharacteristics,
F
p
needs to be reduced to 1.0 N if
t
1
equals 0.0115 s. This 10
simulation is shown in Figure 13.44.
To simulate larger saccades with main sequence characteristics, the time constants for the
agonist and antagonist active-state tensions can be kept at the same values as the 10
saccades
or made functions of saccade amplitude (see [1] for several examples of amplitude-dependent
time constants). Main sequence simulations for 15
and 20
saccades are obtained with
t
ac
remainsat0.018sand
F
p
¼
1.3 N
and the time constants are both fixed at 0.018 s (the first case) by changing
t
1
to 0.0155 and
0.0223 s, respectively. For example, the 20
simulation results are shown in Figure 13.45,withapeak
velocity of 682
s
1
and a duration of 60 ms.
In general, as
F
p
increases,
t
1
decreases to maintain the same saccade amplitude. Additionally,
peak velocity increases as
F
p
increases. For the saccade amplitude to remain a constant as either
or both of the time constants increase,
F
p
should also increase.
