Does planning a different trajectory influence the choice of grasping points?

Abstract

We examined whether the movement path is considered when selecting the positions at which the digits will contact the object’s surface (grasping points). Subjects grasped objects of different heights but with the same radius at various locations on a table. At some locations, one digit crossed to the side of the object opposite of where it started. In doing so, it moved over a short object whereas it curved around a tall object. This resulted in very different paths for different objects. Importantly, the selection of grasping points was unaffected. That subjects do not appear to consider the path when selecting grasping points suggests that the grasping points are selected before planning the movements towards those points.

Do obstacles affect the selection of grasping points?

“…The effects on the latter variable that we found for object location and starting position have been reported before (Schot et al, 2010; Voudouris et al, 2010), so we will concentrate our discussion on the effects of the obstacle. The horizontal grip orientation was further counter-clockwise when the thumb's grasping point was constrained, but not systematically further clockwise when the finger's grasping point was constrained.…”

“…4 and 8). Considering our previous finding that the path along which the digits move does not influence the grasping points (Voudouris et al, 2010) we believe that it is the final arm configuration that is critical . Subjects moved towards the object with deviations away from the obstacle to maintain a safe distance from it (Tresilian, 1998).…”

“…However, we have previously shown that the arm and hand configuration at the time of contact, rather than during the movement towards the object, are critical when selecting grasping points on an isolated object 5 cm (Voudouris, Brenner, Schot, & Smeets, 2010), so perhaps obstacles only influence how one moves. We here examined the role of obstacles in selecting grasping points when grasping a sphere (see Fig.…”

Ultra-fast selection of grasping points

“…We can distinguish between two aspects of grasping (once a target object has been identified): selecting grasping points on the object (Cuijpers et al 2004;Voudouris et al 2010) and bringing the digits to the selected points (Smeets and Brenner 1999). Most of the fast corrections that have been reported are concerned with the control of movements to selected points.…”

Skill Acquisition and Training

“…For example, if one's intent is to grasp an object, the trajectory that the movement takes will be a function of the position of the object to be grasped, the current position of the limb to be moved, and the points at which the object will be grasped (Voudouris, Brenner, Schot, & Smeets, 2010). Movement does not occur in a perceptual vacuum but is dependent on perceptual information.…”