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Inverting the planning gradient: adjustment of grasps to late segments of multi-step object manipulations

Abstract

When someone grasps an object, the grasp depends on the intended object manipulation and usually facilitates it. If several object manipulation steps are planned, the first step has been reported to primarily determine the grasp selection. We address whether the grasp can be aligned to the second step, if the second step’s requirements exceed those of the first step. Participants grasped and rotated a dial first by a small extent and then by various extents in the opposite direction, without releasing the dial. On average, when the requirements of the first and the second step were similar, participants mostly aligned the grasp to the first step. When the requirements of the second step were considerably higher, participants aligned the grasp to the second step, even though the first step still had a considerable impact. Participants employed two different strategies. One subgroup initially aligned the grasp to the first step and then ceased adjusting the grasp to either step. Another group also initially aligned the grasp to the first step and then switched to aligning it primarily to the second step. The data suggest that participants are more likely to switch to the latter strategy when they experienced more awkward arm postures. In summary, grasp selections for multi-step object manipulations can be aligned to the second object manipulation step, if the requirements of this step clearly exceed those of the first step and if participants have some experience with the task.

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Notes

  1. We report Greenhouse-Geisser corrected p-values but uncorrected dfs. Effect sizes are reported as described in Lakens (2013).

  2. A split-plot ANOVA with within-participant factor block (5, 6, 7, 8) and between-participant factor group revealed neither a main effect of block (F[3,171] = 0.038, p = .959, η2 p = 0.001) nor an interaction between block and two-step sequence: F(6,171) = 0.451, p = .766, η2 p = 0.016.

  3. For one participant, ΔGO30° was − 1.03°. The within-participant standard deviation of GO for clockwise and counterclockwise 30° rotations for this participant was 31° and 16°, respectively. For the remaining 59 participants, ΔGO30° had a positive value.

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Acknowledgements

This work was funded by Grant HE 6710/2-1 of the German Research Foundation (DFG) granted to Oliver Herbort. We thank Albrecht Sebald and Georg Schüssler for technical support.

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Correspondence to Oliver Herbort.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Mathew, H., Kunde, W. & Herbort, O. Inverting the planning gradient: adjustment of grasps to late segments of multi-step object manipulations. Exp Brain Res 235, 1397–1409 (2017). https://doi.org/10.1007/s00221-017-4892-9

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  • DOI: https://doi.org/10.1007/s00221-017-4892-9

Keywords

  • Grasping
  • Movement planning
  • End-state comfort effect
  • Object manipulation
  • Sequential action