title: Movement variability near goal equivalent manifolds: fluctuations, control, and model-based analysis.
abstract: Fluctuations in the repeated performance of human movements have been the subject of intense scrutiny because they are generally believed to contain important information about the function and health of the neuromotor system. A variety of approaches has been brought to bear to study these fluctuations. However it is frequently difficult to understand how to synthesize different perspectives to give a coherent picture. Here, we describe a conceptual framework for the experimental study of motor variability that helps to unify geometrical methods, which focus on the role of motor redundancy, with dynamical methods that characterize the error-correcting processes regulating the performance of skilled tasks. We describe how goal functions, which mathematically specify the task strategy being employed, together with ideas from the control of redundant systems, allow one to formulate simple, experimentally testable dynamical models of inter-trial fluctuations. After reviewing the basic theory, we present a list of five general hypotheses on the structure of fluctuations that can be expected in repeated trials of goal-directed tasks. We review recent experimental applications of this general approach, and show how it can be used to precisely characterize the error-correcting control used by human subjects.
authors.affiliation: Dept. of Engineering Science & Mechanics, Penn State University, University Park, PA 16802, USA. Electronic address: jpcusumano@psu.edu.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Cusumano
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Dingwell
mesh_terms: D002490:Central Nervous System / Q000502:physiology*; D006040:Goals; D006801:Humans; D008962:Models, Theoretical; D009046:Motor Neurons / Q000502:physiology*; D009048:Motor Skills / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D016571:Neural Networks, Computer; D004856:Postural Balance / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D013177:Sports / Q000502:physiology; D013269:Stochastic Processes; D014584:User-Computer Interface; D016138:Walking / Q000502:physiology
keywords: 2221 Sensory & Motor Testing; 2240 Statistics & Mathematics; Goal equivalence; Motor redundancy; Motor variability; Sensory and motor testing; Statistics and mathematics