Postural stabilization of looking

The authors studied relations between postural sway, optical flow, and cons traints on posture imposed by a suprapostural looking task. Optical how res ulted from unperturbed sway and was not imposed by the experimenters. Parti cipants fixated a distant target or a nearby target. In the key condition, participants looked past (i.e., ignored) a nearby target to fixate the dist ant target. The authors recorded the variability of head position as a meas ure of the amplitude of postural sway. In 5 of 7 experiments, sway variabil ity was influenced by the location of the fixated target not by the distanc e of the nearest visible surface (the unfixated nearby target). Postural sw ay was modulated to facilitate the performance of suprapostural tasks and w as not driven by optical flow in an autonomous (task-independent) manner. T he authors concluded that posture can be understood only in the context of explicit manipulations of suprapostural tasks.