The kinematics of far - near re - fixation saccades 1 Bernhard

25 We have analyzed the three-dimensional spatio-temporal characteristics of saccadic re26 fixations between far and near targets in three behaviorally trained rhesus monkeys. The 27 kinematics underlying these rapid eye movements can be accurately described by rotations of 28 the eyes in four different planes, namely first dis-conjugate rotations in the horizontal plane 29 of regard converging the eyes towards the near target followed by rotations in each eye’s 30 vertical direction-plane and finally dis-conjugate rotations in a common fronto-parallel plane. 31 This compounded rotation of the eye was underlying an initially fast rising variable torsion 32 that typically overshot the final torsion, which the eyes attained at the time of target 33 acquisition. The torsion consisted of a coarse widely varying component of opposite polarity 34 in the two eyes, which contained a more robust much smaller modulation that sharply 35 increased towards the end of saccades. The reorientation of the eyes in torsion depended on 36 each eye’s azimuth, elevation and target distance. We conclude that re-fixation saccades are 37 generated by motor commands that control ocular torsion in concert with the saccade38 generator, which operates in Donders-Listing kinematics underlying Listings law. 39 40 41