When you jaywalk, your ability to keep track of that oncoming truckdespite your constantly changing position can be a lifesaver. Butscientists do not understand how such constant updating of depth anddistance takes place, suspecting that the brain receives informationnot just from the eye but also from the motion-detecting vestibularsystem in the middle ear.
In studies with monkeys reported in the October 6, 2005, issue ofNeuron, Nuo Li and Dora Angelaki of Washington University School ofMedicine in St. Louis have demonstrated how such depth motion isupdated and strongly implicated the vestibular system in that process.
In their experiments, the researchers trained the monkeys toperform memory-guided eye movements. The animals were first shown alight a fixed distance away from their head. Then the researchersflashed one of eight other, closer "world-fixed" target lights. Next,with the room lights turned off, the monkeys were moved either forwardor backward and the fixed-distance light flashed, signaling the monkeysthat they should look at where they remembered the world-fixed lighthad flashed. Finally, the room lights and target light were turned on,so the monkey could make any corrective eye movement to the re-littarget. For comparison, the researchers also conducted experiments inwhich the monkeys were not moved.
Such an experimental design using passive motion enabled theresearchers to study depth-tracking in the absence of any clues themonkeys might have gleaned from their own motor movements--leavingvestibular system as the most likely source of information.
Finally, the researchers eliminated the vestibular systems intwo of the monkeys and performed the same eye-movement experiments.
They found that the eye motion of monkeys in the firstexperiments indicated that they were clearly able to update theirperception of the depth of the target, even in the absence ofinformation from their own motor movements. By contrast, the monkeysthat lacked vestibular systems showed compromised ability in the task.
"These results demonstrate not only that monkeys can updateretinal disparity information but also that intact vestibular motioncues are critical in reconstructing three-dimensional visual spaceduring motion in depth," concluded Li and Angelaki.
The researchers include Nuo Li and Dora E. Angelaki of WashingtonUniversity School of Medicine in St. Louis. The work was supported byNIH grants.
Li et al.: "Updating visual space during motion in depth."Neuron, Vol. 48, 149-158, October 6, 2005, DOI10.1016/j.neuron.2005.08.021 www.neuron.org.
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