Visuomotor Coordination in Symmetric and Asymmetric Bimanual Reaching Tasks.

Abstract

Eye-hand coordination is fundamental to performing any motor activity, from the simplest tasks to skilled operations required of professionals in sports or industry. While coordination of concurrent motor responses has been studied extensively, the factors that drive specific patterns of coupling of the two hand movements are not yet clearly understood. The dissertation discusses the organization of bimanual coordination: patterns of movement initiations, movement durations, and spatio-temporal coupling of hand movements as a function of task demand. A model has been proposed to predict how competing visual demands of both hand systems could be met within constraints of the visual system. This study investigates the role of visual feedback in mediating control of bimanual movements using two reach tasks, one with each hand, to targets with different accuracy constraints. A strong tendency to temporally synchronize movements of both hands was observed. Although synchronized until peak-velocity, patterns of coordination of terminal phases of movements varied as a function of task difficulty. Spatial symmetry was compromised in favor of temporal symmetry. Patterns of spatial coupling were pre-planned based on the system’s expectations about the time of availability of visual feedback for completion of the secondary task.With practice, different eye-hand coordination strategies emerged as a function of task precision. Although both movements were performed simultaneously, feedback resources were prioritized to process movement corrections of only one task at a time. In symmetric task conditions, visual attention was consistently allocated first to the left-hand-task (primary), and performance of the right-hand-task was secondary, dependent on successful performance of the primary task. This behavior indicates asymmetry in feedback requirements of the two hand systems.

An integrated control model of the two hands and gaze system was developed to simulate self-paced bimanual tasks with only high-level inputs. This model sequences movement phases as a function of task parameters and mediates optimal allocation of visual resources to both hands. Combined with an attention-allocation mechanism based on a stochastic probability of successful task completion, the model accurately produces the diverse visuomotor coordination phenomena observed in laboratory (task prioritization, gaze transitions and production of realistic multimode hand velocity profiles).