The Journal of Neuroscience, 2001, 21:RC126:1-5
RAPID COMMUNICATION
Stereopsis Outweighs Gravity in the Control of the Eyes
Hubert
Misslisch1,
Douglas
Tweed2, and
Bernhard J. M.
Hess1
1 Department of Neurology, University of Zurich,
CH-8091 Zurich, Switzerland, and 2 Departments of
Physiology and Medicine, University of Toronto, Toronto, M5S 1A8,
Canada
The eyes are controlled by multiple brain circuits, some
phylogenetically old and some new, whose aims may conflict. Old otolith reflexes counterroll the eyes when the head tilts relative to gravity.
Newer vergence mechanisms coordinate the eyes to aid stereoptic vision.
We show that counterroll hinders stereopsis, weakly when you look into
the distance but strongly when you look near. The resolution of this
conflict is that counterroll virtually vanishes when monkeys look
close, i.e., stereopsis overrides gravity-driven reflexes but only on
near gaze. This balance between gyroscopic and stereoptic mechanisms
explains many other puzzling features of primate gaze control, such as
the weakness of our otolith-ocular reflexes even during far viewing and
the strange geometry of the primate counterpitch reflex, which rolls
the eyes clockwise when monkeys look leftward while their heads are
tipped nose up, but rolls them counterclockwise when the monkeys look
rightward, and reverses this pattern when the head is tipped nose down.
Key words:
stereopsis; vergence; otolith-ocular; vestibulo-ocular; ocular torsion; vision; 3-D eye movements
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