Saccadic foveation of a moving visual target in the 1 rhesus monkey 2 3

24 When generating a saccade toward a moving target, the target displacement that 25 occurs during the period spanning from its detection to the saccade end must be taken 26 into account in order to accurately foveate the target and to initiate its pursuit. 27 Previous studies have shown that these saccades are characterized by a lower peak 28 velocity and a prolonged deceleration phase. In some cases, a second peak eye 29 velocity appears during the deceleration phase, presumably reflecting the late 30 influence of a mechanism that compensates for the target displacement occurring 31 before saccade end. The goal of this work was to further determine in the head 32 restrained monkey the dynamics of this putative compensatory mechanism. A step33 ramp paradigm, where the target motion was orthogonal to a target step occurring 34 along the primary axes, was used to estimate from the generated saccades, a 35 component induced by the target step and another one induced by the target motion. 36 Resulting oblique saccades were compared to saccades to a static target with matched 37 horizontal and vertical amplitudes. This study permitted to estimate the time taken for 38 visual motion-related signals to update the programming and execution of saccades. 39 The amplitude of the motion-related component was slightly hypometric with an 40 undershoot that increased with target speed. Moreover, it matched with the 41 eccentricity that the target had 40-60 ms before saccade end. The lack of significant 42 difference in the delay between the onsets of the horizontal and vertical components 43 between saccades directed toward a static target and those aimed at a moving target 44 questions the late influence of the compensatory mechanism. The results are discussed 45 within the framework of the “dual drive” and “remapping” hypotheses. 46