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

Abstract

As numerous movement options are available in reaching and grasping, of particular interest are what factors influence an individual's choice of action. In the current study a preferential reaching task was used to assess the propensity for right handers to select their preferred hand and grasp a coffee mug by the handle in both independent and joint action object manipulation contexts. Mug location (right-space, midline, and left-space) and handle orientation (toward, away, to left, and to right of the participant) varied in four tasks that differed as a function of intention: (1) pick-up (unimanual, independent); (2) pick-up and pour (bimanual, independent); (3) pick-up and pass (unimanual, joint action); and (4) pick-up, pour and pass (bimanual, joint action). In line with previous reports, a right-hand preference for unimanual tasks was observed. Furthermore, extending existing literature to a preferential reaching task, role differentiation between the hands in bimanual tasks (i.e., preferred hand mobilizing, non-preferred hand stabilizing) was displayed. Finally, right-hand selection was greatest in right space, albeit lower in bimanual tasks compared to what is typically reported in unimanual tasks. Findings are attributed to the desire to maximize biomechanical efficiency in reaching. Grasp postures were also observed to reflect consideration of efficiency. More specifically, within independent object manipulation (pick-up; pick-up and pour) participants only grasped the mug by the handle when it afforded a comfortable posture. Furthermore, in joint action (pick-up and pass; pick-up, pour and pass), the confederate was only offered the handle if the intended action of the confederate was similar or required less effort than that of the participant. Together, findings from the current study add to our knowledge of hand and grasp selection in unimanual and bimanual object manipulation, within the context of both independent and joint action tasks.

Keywords: grasp selection; hand selection; object location; object orientation; preferential reaching; task intention.

FIGURE 1

Study set up. Participant sat in the chair, researcher sat across from the participant.

FIGURE 2

The three-way interaction of task, location and handle revealed the most right-hand selection was displayed in right-space, among other effects, which are explained in text. Standard errors bars are displayed.

FIGURE 3

The three-way interaction of task, location and handle, where only bimanual tasks are plotted (see supplementary material for additional data). Although lower than what is normally observed in unimanual tasks, the most right-hand selection was displayed in right-space, among other effects, which are explained in text. Standard errors bars are displayed.

FIGURE 4

Regardless of the handle orientation, participants grasped the mug by the handle most often in pick-up and pour. Standard errors bars are displayed.

FIGURE 5

The mug was grasped by the handle most often when it faced toward the participant, and when it faced to the left in pour. Standard errors bars are displayed.

FIGURE 6

Regardless of the mug’s location, the handle was grasped most often when it faced toward the participant and least often when it faced away. Standard errors bars are displayed.