Context Dependence of Manual Grasping Movements in Near Weightlessness

Abstract

We have shown before that human subject grasping performance differs in an everyday-like context with that observed in a laboratory context. The purpose of the present study was to determine whether reported deficits in weightlessness are more pronounced when grasping is performed as part of everyday-like behavior rather than as an isolated laboratory-type response. The grasping performance of 12 participants (ages 29 +/- 5 yr) during periods of near weightlessness in parabolic flights was compared. Subjects performed a typical laboratory task (L) where grasping was repetitive, externally triggered, purposeless, and attention-attracting, and an everyday-like task (E) where the movements were part of a rich behavioral pattern, internally initiated, purposeful, and little attended. We registered typical kinematic, force, and gaze parameters, and calculated their within-subject means and variation coefficients. A global parameter comparison showed that the effects of weightlessness on grasping movements were task-dependent: means were more affected in task E (RMS scores 1.29 +/- 0.07 in L compared with 1.74 +/- 0.15 in E) and variation coefficients in task L (RMS score 4.92 +/- 0.53 in L compared to 3.00 +/- 0.22 in E). The results suggest that the effects of weightlessness observed under laboratory conditions can under- or overestimate the effects that emerge during everyday routines.