Suprapostural tasks

Stoffregen, Smart, Bardy, & Pagulayan (1999) found that postural sway is often modulated so as to facilitate performance at the supra-postural task task of visual inspection (looking). This is in contrast to the more common assumption that visually-derived information is used primarily or exclusively to facilitate minimization of postural sway. Participants fixated targets at different distances. Earlier research has been interpreted as indicating that posture is controlled by optical flow from the nearest surface in the environment. We included a condition in which participants ignored a nearby surface and instead fixed a distance surface. In this condition, flow from nearby surface was available, but was irrelevant to the suprapostural looking task. As we had predicted, the amplitude of postural sway was related to the distance of fixation, and not to the distance of environmental surfaces, per se.

Stoffregen, Pagulayan, Bardy, & Hettinger (2000) extended the earlier findings to situations involving on-line changes in fixation distance. We also added a second, more constrained looking task. In addition to looking at simple graphical targets, in a second condition participants searched blocks of text for designated target letters. Results showed that the fixation distance effect can be observed across on-line changes in fixation distance. In addition, the distance effect was preserved during reading, and its magnitude is increased.

Affordance learning through body sway


Stoffregen, T. A., Yang, C.-M., Giveans, M. R., Flanagan, M., & Bardy, B. G. (2009). Movement in the perception of an affordance for wheelchair locomotion. Ecological Psychology, 21, 1-36.

Yu, Y., & Stoffregen, T. A. (2009, July). Locomotor and postural contributions to affordance perception. Talk presented at the 15th International Conference on Perception and Action, Minneapolis, MN.

Supported by a grant from the National Science Foundation.

Postural stabilization of visually-guided eye movements

In the study of Stoffregen, Pagulayan, Bardy, & Hettinger (2000) variation in supra-postural visual tasks involved changes in the difficulty of fixation (presumably, participants had to position their eyes more carefully in reading letters than in looking at a blank target), but also changes in the difficulty of eye movements (inspection tolerated by did not require eye movements, while the letter search task required the use of precisely guided eye movements). In a new study (currently under review), we examined relations between postural control and the execution of eye movements. Participants used eye movements to track very simple, side-to-side motion of targets on a computer monitor. Sway in this condition was compared with sway during fixation of a stationary target, and with sway when the eyes were closed and participants moved their eyes behind their lids. Sway was reduced during visually guided eye movements, relative to sway during stationary fixation, and relative to sway during eye movements with the eyes closed. We conclude that postural control can be used to facilitate the control of eye movements, but that this occurs only when eye movements are visually guided. When the eyes are closed, body sway has no effect on the accuracy of eye movements.


Stoffregen, T. A., Bardy, B. G., Bonnet, C. T., Hove, P., & Oullier, O. (2007). Postural sway and the frequency of horizontal eye movements. Motor Control, 11, 86-102.

Stoffregen, T. A., Bardy, B. G., Bonnet, C. T., & Pagulayan, R. J. (2006). Postural stabilization of visually guided eye movements. Ecological Psychology, 18, 191-222.

Carried out in collaboration with Dr. Benoît G. Bardy of the Universite' Montpellier-1. Supported by the National Science Foundation, the University of Montpellier-1, and the Institut Universitaire de France.

Task-specific postural responses to imposed optic flow


Stoffregen, T. A., Hove, P., Schmit, J., & Bardy, B. G. (2006). Voluntary and involuntary postural responses to imposed optic flow. Motor Control, 10, 24-33.

Carried out in collaboration with Dr. Benoît G. Bardy of the Universite' Montpellier-1. Our international collaboration was supported by grants from the National Science Foundation and the French Centre National de la Recherche Scientifique.

Postural stabilization of visual but not cognitive performance

In several studies, we have shown that the variability of postural movement is related to the level of demand of visual tasks that are performed while standing. Are such postural variations functional? One way to answer this question is to measure postural motion while participants perform different supra-postural tasks that are equated for "mental effort", but that differ in the level of visual demand. In our study, participants performed a visual signal detection task, or they performed mental arithmetic. Using a standard scale for mental workload, we showed that the subjective difficulty of the signal detection and mental arithmetic tasks did not differ. The signal detection task had a high level of visual demand, while the mental arithmetic task had none. The variability of postural motion was reduced during performance of the signal detection task, relative to sway during mental arithmetic. The results support our contention that task-specific changes in sway were functional. The results also suggest that theorists and experimenters may need to distinguish clearly between perceptual and non-perceptual supra-postural tasks in research relating postural to supra-postural activity (e.g., the dual task paradigm).


Stoffregen, T. A., Hove, P., Bardy, B. G., Riley, M. A., Bonnet, C. T. (2007). Postural stabilization of perceptual but not cognitive performance. Journal of Motor Behavior, 39, 126-138.