Effects of inverted vision on hand-pointing performance in altered gravity during parabolic flight

An accurate perception of the body and the environment is important for programming pointing accuracy and controlling motor action. The objective of this research effort was to assess the influence of gravity on these cognitive and sensorimotor processes. The integration of vestibular, visual, proprioceptive, and cognitive cues was investigated during a pointing task that required eye-hand coordination. Parabolic flights provide a unique environment to understand the specific role of gravity since both vestibular and proprioceptive inputs, as well as the gravitational reference, are altered during the various gravity levels obtained. Additionally, visual input can be altered using prisms that invert the visual scene. Six subjects participated in a within-subject experiment during the 61st ESA and 112th CNES parabolic flight campaigns. Seated subjects performed hand-pointing motions at randomly appearing dots on a 22-inch tactile display during 15 parabolas under three different gravity levels (0G, 1G, 1.8G) and two different visual conditions (normal, up-down inverted). Pointing latency (i.e. reaction time and duration of movement) and pointing accuracy (i.e. error between the target position and the actual hit) were recorded using custom-built software. Results show a statistically significant increase in reaction time and action time (i.e. decrease in performance), and a statistically significant upward shifting in the vertical pointing direction during up-down inverted vision with respect to normal vision. However, data did not reveal statistical significant differences in pointing performance between gravity levels. We discuss the significance of these results regarding the mechanisms of sensory integration for eye-hand coordination and briefly propose future research directions in this area.