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Stefano Ramat, Jeffrey T. Somers, Vallabh E. Das, R. John Leigh; Conjugate Ocular Oscillations during Shifts of the Direction and Depth of Visual Fixation. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1681-1686.
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purpose. To characterize dynamic properties of combined saccade–vergence eye
movements that occur as the point of visual fixation is shifted between
objects lying in different directions and at different depths.
methods. Using the scleral search-coil technique, eye movements were measured in
10 normal subjects as they made voluntary, disjunctive gaze shifts
comprising a range of saccades and vergence movements.
results. By analyzing eye acceleration records, the authors identified
small-amplitude (0.2–0.7°), high-frequency (23–33 Hz), conjugate
horizontal oscillations of the eyes during the vergence movement that
followed the initial saccade. When the shift of the fixation point
required a large vergence component (17°), every subject showed these
oscillations; they were present in approximately a third of responses.
Approximately 5% of responses showed oscillations that had horizontal
and vertical components. Oscillations were less prominent with shifts
that had smaller vergence components and were absent after saccades
made between targets located at optical infinity.
conclusions. These findings suggest that a common mechanism gates both the saccadic
and vergence components of disjunctive gaze shifts, a likely candidate
being the pontine omnipause neurons. When a saccade is immediately
followed by a prolonged vergence movement, the omnipause neurons remain
silent, leading to small-amplitude saccadic oscillations. Shifts in the
point of visual fixation that require a large vergence movement may be
a useful experimental strategy to induce saccadic
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