Biomedical Engineering Reference
In-Depth Information
13.8 THE 2009 LINEAR HOMEOMORPHIC
SACCADIC EYE MOVEMENT MODEL
In this section, we further explore the fast eye movement system that has postsaccade
behavior, including normal saccades and those with a dynamic or a glissadic overshoot based
on a model by Zhou, Chen, and Enderle [50] and Enderle and Zhou [18]. Postsaccade
phenomena, such as a dynamic or a glissadic overshoot, are usually observed during human
saccades [47]. In dynamic overshoot, the eyes move beyond the target, and then, with a quick
saccade-like return with no time delay, the eyes move back to the target. Glissadic overshoot
is similar to dynamic overshoot but with a return that is slower. To analyze postsaccade
behavior, the neural input to the muscles is now described by a pulse-slide-step of neural
activity, supported by physiological evidence [26]. The slide is a slow exponential transition
from the pulse to the step.
The oculomotor plant is shown in Figure 13.46. It should be noted that the passive elas-
ticity of the eyeball in Figure 13.46 is changed from the model in Figure 13.41 that included
two Voigt passive elements connected in series to a single Voigt element. The Voigt element
with time constant 0.02 s is used in the model presented here. The other Voigt element, with
a time constant of 1 s, is neglected, since it has an insignificant effect on the accuracy
because we are modeling a single saccade and not a series of saccades. Further, eliminating
x
θ
x p1
x p4
x 4
T ag
x 1
T ant
J p
B 2
K se
B 2
K se
x p2
x p3
x 3
B p
K p
x 2
F ag
K lt
F ant
K lt
B 1
B 1
FIGURE 13.46 Oculomotor plant used for analyzing saccades with postsaccade behavior.
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