Structural constraints on the coordination of concurrent rotations of the head and a steering device

Concurrent movements of different effectors are subject to structural constraints that facilitate certain patterns of coordination but impede others. The constraints for concurrent rotations of the head and a bimanually operated steering device were explored in two experiments. To indicate structural constraints, the difference between concurrent periodic rotations in same and different directions with respect to the variable error of synchronization was used. The first experiment showed less error for rotations in same directions than for rotations in opposite directions. In the second experiment, the same result was obtained with a horizontal and a backward-tilted steering wheel. Adding gaze shifts to head oscillations increased the accuracy of synchronization but did not affect the difference between both coordination patterns. In contrast to the synchronization of head and steering device, the variable error of synchronization of gaze and steering wheel did not differ between both modes of coordination; the error was again reduced when head oscillations were added to the saccades between eccentric fixation targets. This suggests space related (or allocentric) constraints, which most likely originate from concurrent specifications of movement directions in coupled spatiotopic maps so that the specification of rotations in the same direction is facilitated in comparison to rotations in opposite directions.