Public Thesis Defense of Simon VANDERGOOTEN - ICTEAM/IONS

From Earth to Orbit: influence of graviceptive inputs on reach and grip behavior

Wednesday November 19th, 2025, 4:30pm - Room A03 SCES - Place des Sciences, 2, 1348 Louvain-la-Neuve

Gravity has long been proposed to play a unique role in sensorimotor coordination, yet the mechanisms underlying gravity-based visuomotor realignment remain elusive. In this thesis, by studying targeted arm movements performed by astronauts before, during, and after missions on the ISS, we made an unexpected observation bearing on the fundamental question of gravity’s role in aligning visuomotor reference frames. Measurements on Earth and in weightlessness revealed a systematic drift in hand-path orientation, but only under very specific conditions which led us to propose an ‘inverted pendulum’ hypothesis to explain the saliency of the gravity vector for sensorimotor coordination.

To further probe the mechanisms underlying this drift, we manipulated body orientation relative to gravity using a rotating chair in the lab. With eyes closed, drift occurred when the body was tilted but not in the upright posture. These results indicate that upright stance provides a unique condition for stable and consistent sensorimotor coordination, supporting recent hypotheses that maintaining the head upright is advantageous for stabilizing visuomotor transformations.

Finally, using data obtained in weightlessness and numerical simulations based on optimal control, we show that directional asymmetries typically observed for the velocity profiles of vertical movements also occur for horizontal ones but arise from biomechanical effects rather than optimization processes. Moreover, we found that astronauts apply excessive grasping forces in the unusual situation of having to decelerate an object moving upward, which persists even after spending several months in space.

All these works together emphasize the crucial role played by gravity in movement planning and execution during daily life tasks such as object manipulation.

Jury members :

Prof. Philippe Lefèvre  (UCLouvain)(Supervisor)

Prof. Pierre-Antoine Absil  (UCLouvain) (President)

Prof. Frédéric Crevecoeur  (UCLouvain) (Secretary)

Prof. Lionel Bringoux (Aix Marseille Université, France)

Prof. Pierre Denise (Université CAEN Normandie, France)

Prof. Joseph McIntyre (Ikerbasque & Tecnalia, Spain)

Pay attention : the public defense of Simon Vandergooten will also take place in the form of a videoconference