Adaptation of multisensory integration for visuo-manual coordination during 60 days of bedrest

Human eye-hand coordination relies on the integration of visual and proprioceptive cues, a process influenced by gravitational inputs1. This study investigates whether the human preference for an upright head posture during visuomotor tasks results from evolutionary constraints (phylogeny) or individual adaptation (ontogeny). Volunteers completed 60 days of bedrest, performing virtual reality tests assessing their performance in cross-modal visuo-proprioceptive, unimodal visual, and unimodal proprioceptive tasks. Compared with controls, bedrest participants initially exhibited impaired cross-modal transformations, followed by partial adaptation. However, after resuming an upright posture, their responses variability and visual dependency remained greater than in controls, indicating lasting effects of prolonged head-gravity misalignment. These findings support an ontogenetic basis for the preference for a gravitationally-aligned head posture, with implications for spaceflight adaptation and vestibular rehabilitation.