18th annual conference on manual control.pdf - Acgsc.org

INTRODUCTION
We have undertaken a modeling effort to describe the pupillary
light reflex system, including the retina, pretectum,
Edinger-Westphal nucleus and iris. There are essentially three
types of behavior which we wish our model to describe: pupillary
escape, pupillary capture, and the asymmetry of the response.
Pupillary escape (as named by Lowenstein and Loewenfeld (1969))
is the phenomenon that, when stimulated with a step input of
light, the pupil will quickly constrict, then slowly dilate.
However, when the pupil is initially small or the intensity of
the input is large, it will constrict more slowly and not
dilate, a process which has been called pupillary capture (Usui
(1974)). Finally, when the pupil is stimulated by a negative
step (decrease in light intensity) the response is a small
dilation. We feel these are some of the dominant characteristics
of the pupillary light reflex system.
Early efforts to model the pupil ( Stark(1959),
Clynes(1961), Troestra(1968), Webster(1971)) dealt mostly with
the pupillary escape and asymmetry phenomena. Semmlow & Stark
(1972) and Semmlow & Chert (1977) developed models utilizing
saturation of the iris to describe the pupillary capture
behavior. Shimizu (1977) proposed a model whereby the time constant
of the reponse changed with the intensity of the stimulus.
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