Affordances Constrain Motor Abundance: A Hypothesis and A Research Programme

Movement control faces a problem of redundancy. In general, there are more degrees of freedom available to solve a task than the task requires. This ‘degrees of freedom’ problem has been reframed as a ‘motor abundance’ feature (Latash, 2012), where the redundancy enables crucial flexibility. The balance between flexibility and control has been proposed to depend on synergies, which are lower-dimensional organisations of movement dynamics into systems that solve the task at hand. There are now several movement analysis methods designed to search for the signatures of synergies (the uncontrolled manifold, Scholz & Schöner, 1999; tolerance-noise-covariation, Cohen & Sternad, 2009, and others) and a great deal of empirical evidence that synergies feature in movement control. However, while all of these analysis methods rely on notions of ‘task’ to constrain movement solutions, they do not come with a formal theory of what a task is or how tasks are perceived. This paper proposes the hypothesis that tasks should be formalised as task-dynamical affordances, and that perceiving these via specifying information is how they constrain synergy formation (effectivities). I lay out the hypothesis, and detail a research programme to investigate the hypothesis, with reference to existing work on throwing.