Postural stabilization of looking

The authors studied relations between postural sway, optical flow, and constraints on posture imposed by a suprapostural looking task. Optical flow resulted from unperturbed sway and was not imposed by the experimenters. Participants fixated a distant target or a nearby target. In the key condition, participants looked past (i.e., ignored) a nearby target to fixate the distant target. The authors recorded the variability of head position as a measure of the amplitude of postural sway. In 5 of 7 experiments, sway variability was influenced by the location of the fixated target not by the distance of the nearest visible surface (the unfixated nearby target). Postural sway was modulated to facilitate the performance of suprapostural tasks and was not driven by optical flow in an autonomous (task-independent) manner. The authors concluded that posture can be understood only in the context of explicit manipulations of suprapostural tasks.