Interactions between force and timing control of repeated actions

Variability is an inherent component in movement and provides an insight into control processes involved in producing motor responses. This thesis investigates the interactions between force and timing processes in the production of repetitive actions from an information processing perspective. Force-time interactions are examined in steady state sequences, sequences with step changes, and steady state sequences with a secondary visual search task as an attentional load. The account of control in normal healthy participants is then applied to describe behaviour of patients with cerebrovascular accidents (CVAs) in two case studies. Interaction was found to be present in variability measures and was quantified using cross-correlation analysis. Overall, results demonstrated that one locus of force-time interaction is at a cognitive level where motor responses are organised for execution. Corresponding changes in magnitude of dependence according to availability of attentional resources and task prioritisation supported this observation. Dependence patterns in patients with CVAs reflected loss of control when task difficulty increased. Finally, based on the findings, a conceptual model describing the interaction is proposed towards the development of a formal model for simulation studies.