Krischan Koerfer¹, Markus Lappe¹; ¹University of Münster

Often the saccade system and the smooth pursuit system have to work in conjunction for optimal gaze behavior. This is especially true for intercepting saccades to a moving target with consecutive pursuit. The extent to which the two systems share a control system and a common neurological representation of motion signals has been debated. Recently, we reported a type of non-rigid motion that cannot be pursued smoothy. Here, we show that the saccade system can briefly activate the pursuit system to compensate for the landing error of the saccade even in absence of any motion signal in the pursuit system. We presented a vortex motion moving horizontally at 5 or 10 degrees per second. Participants were instructed to fixate a red cross and then intercept and pursue the vortex once the red cross vanished. Despite the general inability to pursue the vortex, we measured a substantial pursuit activity within the first 200 milliseconds after the intercepting saccade. After this period, the pursuit gain dropped close to zero across participants. Analysis of the initial pursuit reveals striking trial-by-trial variability and a strong correlation with the saccade landing error. When saccades landed behind the target, pursuit gain was high, whereas when it landed ahead of the target pursuit gain was low or even negative (pursuit direction opposite to target motion). This suggests that the initial pursuit is not driven by the motion signal of the vortex but instead by the expected position error of the saccade. We propose that even in the absence of any motion signal in the pursuit system, the saccade system can activate the pursuit system to compensate for its shortcomings.

Acknowledgements: This work was supported by the German Research Foundation grant DFG La 952-7 and the European Union’s Horizon 2020 research and innovation programme Marie Skodowska-Curie grant agreement No 734227.