Converging evidence shows that hand-actions are controlled at the level of synergies and not single muscles. One intriguing aspect of synergy-based action-representation is that it may be intrinsically sparse and the same synergies can be shared across several distinct types of hand-actions. Here, adopting a normative angle, we consider three hypotheses for hand-action optimal-control: sparse-combination hypothesis (SC) - sparsity in the mapping between synergies and actions - i.e., actions implemented using a sparse combination of synergies; sparse-elements hypothesis (SE) - sparsity in synergy representation - i.e., the mapping between degrees-of-freedom (DoF) and synergies is sparse; double-sparsity hypothesis (DS) - a novel view combining both SC and SE - i.e., both the mapping between DoF and synergies and between synergies and actions are sparse, each action implementing a sparse combination of synergies (as in SC), each using a limited set of DoFs (as in SE). We evaluate these hypotheses using hand kinematic data from six human subjects performing nine different types of reach-to-grasp actions. Our results support DS, suggesting that the best action representation is based on a relatively large set of synergies, each involving a reduced number of degrees-of-freedom, and that distinct sets of synergies may be involved in distinct tasks.
Evidence for sparse synergies in grasping actions
Nature Publishing Group, London , Regno Unito
Scientific reports (Nature Publishing Group) 8 (2018). doi:10.1038/s41598-017-18776-y
info:cnr-pdr/source/autori:Prevete, Roberto and Donnarumma, Francesco and d'Avella, Andrea and Pezzulo, Giovanni/titolo:Evidence for sparse synergies in grasping actions/doi:10.1038/s41598-017-18776-y/rivista:Scientific reports (Nature Publishing Group)/a