BRIEF REPORT Postural Effects of the Scaled Display of Visual Foot Center of Pressure Feedback Under Different Somatosensory Conditions at the Foot and the Ankle Nicolas Vuillerme, PhD, Romain Bertrand, BSc, Nicolas Pinsault, MSc, PT ABSTRACT. Vuillerme N, Bertrand R, Pinsault N. Postural effects of the scaled display of visual foot center of pressure feedback under different somatosensory conditions at the foot and the ankle. Arch Phys Med Rehabil 2008;89:2034-6. Objectives: To assess the effects of the scaled display of visual foot center of pressure (COP) feedback on upright pos- tural control under different somatosensory conditions at the foot and the ankle. Design: Before and after intervention trials. Setting: University medical bioengineering laboratory. Participants: Young healthy adults (N=8; mean age, 232.5y; mean body weight, 76.811.2kg; mean height, 179.86.8cm). Interventions: Participants were asked to stand upright, as immobile as possible, in 3 visual conditions: a stationary cross feedback (SC-FB) condition and 2 different foot COP feedback (COP-FB) conditions involving increasing scale displays of 2:1 (COP-FB2) and of 10:1 (COP-FB10). These latter conditions correspond to the ratio between the COP displacement on the screen and the actual COP displacement measured by the force platform. This postural task was executed on 2 (firm, foam) support surface conditions. In the foam condition, a 2-cm thick foam support surface was placed under the participants’ feet to alter the quality and/or quantity of somatosensory information at the foot and the ankle. Main Outcome Measure: COP displacements were re- corded using a force platform. Results: In the firm support surface condition, no significant difference was observed between the COP-FB2 and the SC-FB conditions, whereas the COP-FB10 condition yielded de- creased COP displacements relative to the SC-FB condition. In the foam support surface condition, both the COP-FB2 and the COP-FB10 conditions yielded decreased COP displacements relative to the SC-FB condition, with a greater stabilizing effect in the COP-FB10 than COP-FB2 condition. Conclusions: The postural effects of the scale display of visual COP feedback differed depending on the somatosensory conditions at the foot and the ankle. These findings suggest that increased reliance on augmented sensory information for con- trolling upright posture in conditions of altered somatosensory input from the foot and ankle could have implications in clinical and rehabilitative areas. Key Words: Biofeedback (Psychology); Posture; Pressure; Rehabilitation; Somatosensory disorders; Vision. © 2008 by the American Congress of Rehabilitation Medi- cine and the American Academy of Physical Medicine and Rehabilitation A COMMON METHOD OF balance training and rehabili- tation consists of giving patients visual feedback informa- tion about their own foot COP displacements in addition to natural sensory cues. 1,2 Recent studies 3,4 reported that the effectiveness of the COP feedback in improving upright pos- tural control is strongly linked to its scale display, correspond- ing to the ratio between the real displacements of the COP, as measured by the force platform, and their visualization on the monitor screen. It is possible that the effectiveness of this protocol also depends on the somatosensory conditions at, and so input from the foot and the ankle, which have been shown to play an important role in postural control during quiet standing. 5-7 Our study was designed to address this issue by comparing the effects of scale display of visual COP feedback on upright postural control under different somatosensory con- ditions at the foot and the ankle. METHODS Participants A total of 8 healthy young men (mean age, 23.02.5y; mean body weight, 76.811.2kg; mean height, 179.86.8cm) vol- untarily participated and were blinded to the study’s purpose. They gave their informed consent to the experimental proce- dure as required by the Declaration of Helsinki (1964) and the local ethics committee. None of the subjects had any history of motor problems, neurologic disease, vestibular impairment, eye disease, or abnormality that might have influenced their balance. All subjects were evaluated by an ophthalmologist and had normal or corrected-to-normal vision with glasses or con- tact lenses. Task and Procedures Participants stood barefoot on a force platform a (sampling frequency, 64Hz), feet abducted at 30°, heels separated by 3cm, and their arms hanging loosely by their sides. They were asked to remain as immobile as possible in 3 visual conditions. In the SC-FB, they were required to fixate on the intersection of a black cross (20  25cm) placed on a white wall 1m in front of From the Laboratoire TIMC-IMAG, Grenoble, France. Supported by the Ministère de l’Education Nationale de la Recherche et de la Technologie (MENRT), France. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organi- zation with which the authors are associated. Reprint requests to Nicolas Vuillerme, PhD, Laboratoire TIMC-IMAG, Faculté de Médecine, Grenoble cédex 38706, France, e-mail: nicolas.vuillerme@imag.fr. 0003-9993/08/8910-00148$34.00/0 doi:10.1016/j.apmr.2008.03.017 List of Abbreviations ANOVA analysis of variance COP center of pressure COP-FB visual COP feedback SC-FB visual stationary cross feedback 2034 Arch Phys Med Rehabil Vol 89, October 2008