Biomedical Engineering Reference
In-Depth Information
The agonist and antagonist active-state tensions are given by the following low-pass
filtered pulse-step waveforms and are illustrated along with their corresponding neuro-
logical control signals in Figure 13.11.
0
1
t
t
ac
@
e
A
u
ðÞ
ut
t
1
F
ag
¼
F
g
0
u
ð
t
Þþ
F
p
þ
F
g
0
F
p
ð
ð
Þ
Þ
ð
13
:
36
Þ
0
1
t
t
t
ð
Þ
1
t
ac
1
@
e
A
e
t
de
þ
F
gs
þ
F
p
þ
F
g
0
F
p
F
gs
ut
t
1
ð
Þ
t
t
de
F
ant
¼
F
t
0
u
ð
t
Þþ
F
t
0
e
ð
u
ðÞ
ut
t
ð
Þ
Þ
1
0
0
1
1
t
1
t
de
t
t
1
ð
Þ
@
@
A
e
t
ac
A
ut
t
1
þ
F
ts
þ
F
t
0
e
F
ts
ð
Þ
where
F
g
0
¼
initial magnitude of the agonist active-state tension
F
p
¼
pulse magnitude of the agonist active-state tension
F
gs
¼
step magnitude of the agonist active-state tension
F
t
0
¼
initial magnitude of the antagonist active-state tension
F
ts
¼
step magnitude of the antagonist active-state tension
t
ac
¼
activation time constant
t
de
¼
deactivation time constant
t
1
¼
duration of the agonist pulse active-state tension
Final parameter estimates for the saccadic eye movement model are found using the
system identification technique, a frequency response method. The oculomotor system
operates in an open-loop mode while executing a saccade. After completing the saccade,
the central nervous system operates in a closed-loop mode and compares eye and target
position [5]. Figure 13.32 presents a block diagram illustrating the open-loop, closed-loop
operation of the oculomotor system, with the feedback element H operating only during
discrete time intervals when a saccade is not being executed. The system identification is
used to estimate the parameters and the input during the open-loop mode of the saccade.
The steady-state active-state tensions are given by
23
0
:
14
þ
0
:
0185y N for y
<
14
:
F
ag
¼
23
0
:
0283y
N for y
14
:
23
0
:
14
0
:
0098y N for y
<
14
:
F
ant
¼
ð
13
:
37
Þ
23
0
N for y
14
: