Commentary: Hand and Grasp Selection in a Preferential Reaching Task: The Effects of Object Location, Orientation, and Task Intention

Reach-to-grasp actions are the outcomes of several voluntary sub-movements (Jeannerod, 1981, 1984; Paulignan et al., 1997) dependent on the object intrinsic position and shape characteristics (Fattori et al., 2009). The behaviors implemented in order to achieve the proximal goal (i.e., grasping) are further modulated by the action one wants to perform once the object has been grasped (distal goal; Cohen and Rosenbaum, 2004; Cattaneo et al., 2007). These findings suggest that the reason why an object is grasped has an effect on initial prehension kinematics (i.e., " end-goal effect "). Grasping an object often serve the purpose of interpersonal interactions, which are defined by matching behavioral adaptation between subjects (Baldwin, 1992) and, more importantly, joint actions, where the presence of a common goal bounds individuals' behaviors (Sebanz et al., 2006). In these interactive scenarios, the intentions one attributes to his partner are crucial in shaping his own hand-preference for grasping objects as well as the kinematics of his movements. For these different features to be integrated in one movement, reach-to-grasp has been used as a paradigmatic example of the interface between motor behavior and cognition. Recently, Scharoun et al. (2016) aimed at studying hand-preference in an ecological setup including individual and so-called " joint actions " conditions. Here, we argue that adding a social aspect to an individual condition does not capture the essence of joint actions. The authors asked subjects to reach-and-grasp a mug in order to perform four different actions without giving them any instructions on how to perform their grasping. Such paradigms contribute to the field of motor control by clarifying grasping hand-preference embedded in the strategy of grasping. Furthermore, Scharoun and her colleagues proposed four different experimental conditions to test the role of the distal goal on hand-preferences: (1) pickup (unimanual, independent); (2) pickup and pour (bimanual, independent); (3) pickup and pass (unimanual, joint action); and (4) pickup , pour, and pass (bimanual, joint action). The behavioral results of the study show that the first two conditions offer clear support for the dominant hand preference hypothesis during unimanual actions. The study needs to be praised for showing all the aforementioned effects in a realistic paradigm.