Markus Lappe¹, Riccardo Brandolani², Krischan Koerfer¹, Patrizia Fattori², Rossella Breveglieri²; ¹University of Muenster, ²University of Bologna

Reaching toward a moving object requires a complex interplay between different components of the visuomotor system. A novel class of non-rigid motion stimuli, for which certain visuomotor processes such as smooth pursuit are known to fail, offers a tool to study these interactions. Here we investigated how the reaching system integrates visuomotor information in targeting such a non-rigid motion stimulus. Participants fixated on a point while a moving stimulus (a rigid disk or a non-rigid vortex) traveled horizontally from left to right. Each trial began with a button press, followed by stimulus onset. After a variable delay, an auditory cue triggered participants to release the button and reach toward the right edge of the stimulus. In Experiment 1, the stimulus maintained constant velocity (5°/s or 10°/s). In Experiment 2, the stimulus disappeared at reaching onset, leaving only the fixation point on a blank background and requiring participants to reach its remembered position in open-loop fashion. In Experiment 3, the stimulus either continued at the same speed, accelerated, or stopped at reaching onset. All trials ended upon target touch, and sessions were organized into randomized blocks of conditions within each experiment. Both reach planning and execution were consistently impaired when targeting the vortex compared to rigid motion. Reaction times were unaffected by the velocity of the vortex, contrary to what happened when planning a reach for the rigid disk. Memory-guided reaching toward the vortex showed greater undershoots compared to the rigid disk. Visually-guided reaching movements towards the vortex were less accurate than towards the rigid disk, with movement dynamics reflecting impaired positional and velocity encoding during the feedback-driven phase. These findings suggest that the reaching system does not accurately process this non-rigid motion, similar to the deficiency of the oculomotor system in smooth pursuit.

Acknowledgements: EU MSCA SE 101086206 – PLACES; Space It Up by ASI and MUR, n. 2024-5-E.0 - CUP n. I53D2400006000; MulWALK”, 2022BK2NPS_001 - CUP: J53D23010900006 by EU- NextGenerationEU (PNRR)