- Idea that “The entire motor repertoire can be spanned by applying a well-defined set of operations and transformations to these [motor] primitives… according to well-defined syntactic rules.”
- “… new experimental, computational, and conceptual approaches are needed to further advance our understanding of motor compositionality.”
- Many motor tasks can be accomplished many different ways, but the curse of dimensionality is reduced because there is an assumption that “there is a limited vocabulary of primitives.”
- Paper considers:
- How are motor and movement primitives defined
- What is the nature of primitives and how are they represented
- What are the rules related to generation of large repertoire of movements from a small set of elements
- Paper by Chad Jenkins outlines some methods used to find motor primitives, include PCA, HMM, Isomap
- Reaching motions follow stereotyped rules (straight lines with bell-shaped velocity profiles)
- “… hand trajectory can be composed of a few velocity primitives, all with similar shapes characterized by a minimum-jerk […] or log-normal function […]. When stroke patients gain better control over their limb, the number of submovements decreases and their temporal overlap increases, giving smoother trajectories […]” Also babies similar
- Grasping tasks. “Finger movements and forces have been decomposed into basic synergies based either on the idea of uncontrolled manifold […] or on inverse dynamics computations […]. Complicated hand gestures, such as
typing and finger spelling […], also consist of primitives or more complicated sequences that can be decomposed
into a series of elementary units of action.” - “In monkey cortex, electrical microstimulation in primary motor and premotor cortex evokes complex purposeful movements involving many joints and even several body parts […]”
- Not all possible combinations of primitives are used; the way they are put together defines on a syntax
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