Prehension is really reaching and grasping

Abstract

Prehension has traditionally been seen as the act of coordinated reaching and grasping. However, recently, Smeets and Brenner (in Motor Control 3:237-271, 1999) proposed that we might just as well look at prehension as the combination of two independently moving digits. The hand aperture that has featured prominently in many studies on prehension, according to Smeets and Brenner's "double-pointing hypothesis", is really an emergent property related to the time course of the positions of the two digits moving to their respective end points. We tested this double-pointing hypothesis by perturbing the end position of one of the digits while leaving the end position of the opposing digit unchanged. To this end, we had participants reach for and grasp a metallic object of which the side surfaces could be made to slide in and out. We administered the perturbation right after movement initiation. On several occasions, after perturbing the end position of one digit, we found eVects also on the kinematics of the opposing digit. These Wndings are in conXict with Smeets and Brenner's double-pointing hypothesis.

Gravity Affects the Vertical Curvature in Human Grasping Movements

“…We defined the start of the grasping movement as the first moment at which the velocity of the index finger exceeded 0.1 m/s (a value frequently used in grasping studies; e.g., Hesse, Nakagawa, & Deubel, 2010;Schot, Brenner, & Smeets, 2010;van de Kamp & Zaal, 2007;Verheij et al, 2013). The end of the grasping movement was defined as the first moment, after the start of the movement, at which the velocity of the index finger dropped below 0.1 m/s.…”

Kinematic characteristics of tenodesis grasp in C6 quadriplegia

“…1,2,4,5 The kinematics of normal human prehensile movements have been extensively studied since Jeannerod. [6][7][8][9] Indeed, healthy individuals exhibit two prehension components: a reaching phase involving the shoulder, elbow and wrist, and a grasping phase requiring both active finger closure and the opposition of the thumb with the other fingers. 6 These two phases of healthy human prehensile movements are coupled, [6][7][8][9] as shown by the fact that the maximal grip aperture occurs at the moment of peak deceleration, 6 which itself occurs at a fixed time, 60-70% of the reaching phase.…”

“…[6][7][8][9] Indeed, healthy individuals exhibit two prehension components: a reaching phase involving the shoulder, elbow and wrist, and a grasping phase requiring both active finger closure and the opposition of the thumb with the other fingers. 6 These two phases of healthy human prehensile movements are coupled, [6][7][8][9] as shown by the fact that the maximal grip aperture occurs at the moment of peak deceleration, 6 which itself occurs at a fixed time, 60-70% of the reaching phase. 7 Reach-to-grasp movements in individuals with C6 quadriplegia show a series of important kinematics differences compared with healthy control participants.…”

Grasp sensing for human-computer interaction

“…Often the terms grasping and prehension are used interchangeably [17]. For others, prehension is the coordinated act of reaching for an object and grasping it [29]. Kang and Ikeuchi state that a grasping task is composed of pre-grasp phase, static grasp phase, and manipulation phase [13].…”