Gravity Affects the Vertical Curvature in Human Grasping Movements

Abstract

When humans make grasping movements their digits' paths are curved vertically. In a previous study the authors found that this curvature is largely caused by the local constraints at the start and end of the movement. Here the authors examined the contribution of gravity to the part of the curvature that was not explained by the local constraints. Subjects had to grasp a tealight (small cylinder) while sitting on a chair. The authors could rotate the whole setup, including the subject, relative to gravity, whereby the positions of the starting point and of the tealight relative to the subject did not change. They found differences between the paths that are consistent with a direct effect of gravity pulling the arm downward.

Body orientation contributes to modelling the effects of gravity for target interception in humans

“…To test this prediction, we ran a control experiment in which participants tilted backwards by 20°o r 60°were asked to hit a static target in synchrony with the last of a predictable series of stationary audio-visual stimuli. We found that body posture affected significantly arm kinematics, consistent with previous studies on the effects of gravity on arm movements (Papaxanthis et al 1998, Pinter et al 2012Gentili et al 2007;Verheij et al 2013;Gaveau et al 2016), although it did not affect interception timing even after extensive practice.…”

“…; Verheij et al . ; Gaveau et al . ), although it did not affect interception timing even after extensive practice.…”

“…) and grasping (Verheij et al . ). To discriminate between the two alternatives, we ran a control experiment in which participants tilted backwards by 20° or 60° (as in the main experiments) were asked to hit a static target in synchrony with the last of a predictable series of beeps and images (Hening et al .…”

“…However, a main effect of body tilt might also be a result of the effects of gravity on planning and/or executing the arm movement required for interception. Indeed, previous studies showed that kinematic and dynamic features of arm movements depend on movement orientation with respect to gravity during drawing (Papaxanthis et al 1998), pointing (Gentili et al 2007;Pinter et al 2012;Gaveau et al 2016) and grasping (Verheij et al 2013). To discriminate between the two alternatives, we ran a control experiment in which participants tilted backwards by 20°o r 60°(as in the main experiments) were asked to hit a static target in synchrony with the last of a predictable series of beeps and images (Hening et al 1988).…”

Earth-Gravity Congruent Motion Benefits Visual Gain For Parabolic Trajectories

“…There is a growing corpus of research indicating that humans use their knowledge of earth gravity in a broad range of tasks, such as grasping (Verheij, Brenner, & Smeets, 2013), catching and interception (Bosco, Delle Monache, & Lacquaniti, 2012;Jörges, Hagenfeld, & López-Moliner, 2018;Lacquaniti et al, 2013;McIntyre, Zago, & Berthoz, 2001;McIntyre, Zago, Berthoz, & Lacquaniti, 2003;Senot, Zago, Lacquaniti, & McIntyre, 2005;Senot et al, 2012;Zago et al, 2004;Zago, McIntyre, Senot, & Lacquaniti, 2009;, duration estimation (Moscatelli & Lacquaniti, 2011) or the perception of biological motion (Jokisch & Troje, 2003;Maffei et al, 2015;Simion, Regolin, & Bulf, 2008), while arbitrary accelerations are generally neglected (Benguigui & Bennett, 2010;Benguigui, Ripoll, & Broderick, 2003) or used insufficiently. Here we examined ocular pursuit and spatial estimation in a linear prediction motion task that emphasized extrapolation of occluded accelerative object motion.…”