Do humans prefer to see their grasping points?
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To grasp an object the digits need to be placed at suit- able positions on its surface. The selection of such grasping points depends on several factors. Here the authors examined whether being able to see 1 of the selected grasping points is such a fac- tor. Subjects grasped large cylinders or oriented blocks that would normally be grasped with the thumb continuously visible and the final part of the index finger’s trajectory occluded by the object in question. An opaque screen that hid the thumb’s usual grasp- ing point was used to examine whether individuals would choose a grip that was oriented differently to maintain vision of the thumb’s grasping point. A transparent screen was used as a control. Occlud- ing the thumb’s grasping point made subjects move more carefully (adopting a larger grip aperture) and choose a slightly different grip orientation. However, the change in grip orientation was much too small to keep the thumb visible. The authors conclude that humans do not particularly aim for visible grasping points.