Corrections in Grasp Posture in Response to Modifications of Action Goals

et al. (2012) Corrections in Grasp Posture in Response to Modifications of Action Goals. PLoS ONE 7(9): e43015. doi:10.1371/journal.pone.0043015 Corrections in Grasp Posture in Response to Modifications of Action Goals Charmayne M. L. Hughes 0 Christian Seegelke 0 Marnie Ann Spiegel 0 Corinna Oehmichen 0 Julia Hammes 0 Thomas Schack 0 Esteban Andres Fridman, Weill Cornell Medical College, United States of America 0 1 Neurocognition and Action Research Group, Faculty of Psychology and Sport Sciences, Bielefeld University , Bielefeld, Germany , 2 Research Institute for Cognition and Robotics (CoR-Lab) , Bielefeld, Germany , 3 Center of Excellence Cognitive Interaction Technology (CITEC) , Bielefeld, Germany , 4 Institute of Movement Science, Department of Sport and Health Science, Technical University of Munich , Munich , Germany There is ample evidence that people plan their movements to ensure comfortable final grasp postures at the end of a movement. The end-state comfort effect has been found to be a robust constraint during unimanual movements, and leads to the inference that goal-postures are represented and planned prior to movement initiation. The purpose of this study was to examine whether individuals make appropriate corrections to ensure comfortable final goal postures when faced with an unexpected change in action goal. Participants reached for a horizontal cylinder and placed the left or right end of the object into the target disk. As soon as the participant began to move, a secondary stimuli was triggered, which indicated whether the intended action goal had changed or not. Confirming previous research, participants selected initial grasp postures that ensured end-state comfort during non-perturbed trials. In addition, participants made appropriate online corrections to their reach-to-grasp movements to ensure end-state comfort during perturbed trials. Corrections in grasp posture occurred early or late in the reach-to-grasp phase. The results indicate that individuals plan their movements to afford comfort at the end of the movement, and that grasp posture planning is controlled via both feedforward and feedback mechanisms. - Funding: This research was funded by the German Research Foundation (DFG; EC 277). CS gratefully acknowledges the financial support from Honda Research Institute Europe. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: CS gratefully acknowledges the financial support from Honda Research Institute Europe. This does not alter the authors adherence to all the PLoS ONE policies on sharing data and materials. Many of our activities of daily living require that we physically interact with one or more objects. These object manipulations are typically influenced by the physical properties of the object [13], the affordances provided by the object [4], and our intentions [2]. There is also ample evidence suggesting that the action goals of a task are an important determinant in the planning and execution of the motor sequence subtending reach-to-grasp movements [2,5 8]. For example, Marteniuk et al. [2] compared movement trajectories of the hand during a grasping and throwing task to hand trajectories during a grasping and fitting task. Participants took longer to reach for the object, and spent more time in the decelerative portion of the reach-to-grasp phase when the object was to be fitted into a hole (high degree of precision) than when they had to throw it into a bucket (low degree of precision). Similarly, in Ansuini et al. [6] participants reached for a plastic bottle filled with water, and then 1) grasped the bottle without performing any subsequent action (grasp), 2) grasped the bottle, lifted, and then threw the bottle into a cardboard container (lift), 3) grasped, lifted and then placed the bottle on a target (place), 4) grasped, lifted, and then poured the water from the bottle into a container (pour), or 5) grasped, lifted, and then passed the bottle to the experimenter (pass). Ansuini et al. [6] found a gradual shortening of reach duration for the pour, place, pass, and throw conditions, respectively, which likely relates to the accuracy demands associated with the pour and place conditions, compared to the pass and throw conditions. The authors also observed greater middle and ring finger extension in the pour, compared to all other conditions, and larger index-middle and middle-ringer abduction angles for the throw than for all other conditions. In sum, these results indicate that the action end-goals of a task strongly influence the planning and execution of hand and finger movements. The influence of action end-goals on motor planning and execution has also been observed on a more macroscopic level of behavior. In his now seminal bar transport experiment, Rosenbaum et al. [8] asked participants to grasp a horizontally positioned bar and place it in a vertical position to either a left or a right target. When the left side of the bar was to be placed to either the left or right target, all participants grasped the bar with an underhand grip. However, when the right side of the bar was to be placed to either target, participants always grasped the bar with an overhand grip. Thus, regardless of target location, participants grasped the object so that the hand ended in a comfortable posture. The sensitivity toward comfortable (and more controllable) final goal postures is called the end-state comfort effect. Since the original exposition by Rosenbaum et al. [8], subsequent research has provided evidence that comfortable goal postures are represented and planned prior to movement initiation [9]. However, there are instances when we must make rapid adjustments in our behavior due to unexpected changes in the environment. One technique by which researchers can examine compensatory motor control mechanisms is to induce a perceptual or physical change the shape and size of an object [1013], or the location of the target [14]. For example, in Paulignan et al. [14], participants were asked to reach, grasp, and lift one of three possible dowels. In 20% of trials, the light was unexpectedly shifted from the center dowel to either the left or to the right dowel as soon as subject initiated their reaching movements. Paulignan et al. [14] found that perturbing the target location had considerable effects on reach-to-grasp kinematics. Although the initial portion of the movement were similar for non-perturbed and perturbed trials, after approximately 275 ms the spatial trajectories of perturbed trials curved towards the new target location. These adjustments in the spatial trajectory were accompanied by lower peak velocity and earlier time to peak velocity values in perturbed, compared to non-perturbed trials. In sum, results of studies using perturbation paradigms have reported that participants make appropriate on-line adjustment (...truncated)