title: Habit outweighs planning in grasp selection for object manipulation.
abstract: Object-directed grasping movements are adapted to intended interactions with an object. We address whether adjusting the grasp for object manipulation is controlled habitually, based on past experiences, or by goal-directed planning, based on an evaluation of the expected action outcomes. Therefore, we asked participants to grasp and rotate a dial. In such tasks, participants typically grasp the dial with an excursed, uncomfortable arm posture, which then allows to complete the dial rotation in a comfortable end-state. We extended this task by manipulating the contingency between the orientation of the grasp and the resulting end-state of the arm. A one-step (control) group rotated the dial to a single target. A two-step group rotated the dial to an initial target and then in the opposite direction. A three-step group rotated the dial to the initial target, then in the opposite direction, and then back to the initial target. During practice, the two-step and three-step groups reduced the excursion of their grasps, thus avoiding overly excursed arm postures after the second rotation. When the two-step and three-step groups were asked to execute one-step rotations, their grasps resembled those that were acquired during the two-step and three-step rotations, respectively. However, the carry-over was not complete. This suggests that adjusting grasps for forthcoming object manipulations is controlled by a mixture of habitual and goal-directed processes. In the present experiment, the former contributed approximately twice as much to grasp selection than the latter.
authors.affiliation: Department of Psychology, Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany. Electronic address: oliver.herbort@psychologie.uni-wuerzburg.de.
authors.forename: Oliver
authors.initials: O
authors.lastname: Herbort
authors.affiliation: Department of Psychology, Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany. Electronic address: johanna.mathew@uni-wuerzburg.de.
authors.forename: Hanna
authors.initials: H
authors.lastname: Mathew
authors.affiliation: Department of Psychology, Julius-Maximilians-Universität Würzburg, Röntgenring 11, 97070 Würzburg, Germany. Electronic address: kunde@psychologie.uni-wuerzburg.de.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Kunde
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D059031:Anticipation, Psychological; D005260:Female; D006040:Goals; D006184:Habits; D018737:Hand Strength; D006801:Humans; D008297:Male; D009043:Motor Activity; D011597:Psychomotor Performance; D012399:Rotation
keywords: Goal-directed processes; Grasping; Habitual processes; Object manipulation; Planning