The role of spatial acuity in a dynamic balancing task without gravitational cues.

In earlier studies, blindfolded participants used a joystick to orient themselves to the direction of balance in the horizontal roll plane while in a device programmed to behave like an inverted pendulum. In this spaceflight analog situation, position relevant gravitational cues are absent. Most participants show minimal learning, positional drifting, and failure of path integration. However, individual differences are substantial, some participants show learning and others become progressively worse. In Experiment 1, our goal was to determine whether spatial acuity could explain these individual differences in active balancing. We exposed blindfolded participants to passive movement profiles, with different frequency components, in the vertical and horizontal roll planes. They pressed a joystick trigger to indicate every time they passed the start point. We found greater spatial acuity for higher frequencies but no relation between passive spatial accuracy and active balance control in the horizontal roll plane, suggesting that spatial acuity in the horizontal roll plane does not predict performance in a disorienting spaceflight condition. In Experiment 2, we found significant correlations between passive spatial acuity in the vertical roll plane, where participants have task relevant gravitational cues, and early active balancing in the horizontal roll plane. These correlations appeared after participants underwent brief provocative vestibular stimulation by making a pitch head movement during vertical yaw rotation. Our findings suggest that vestibular stimulation may be a valuable part of assessments of individual differences in performance during initial exposure to disorienting spaceflight conditions where there are no reliable gravity dependent positional cues.