Visual information and readiness to receive visual information affects postural control and adaptation
Field:	Sensory systems
Authors:	A. Hafström,* P. -A. Fransson,* T. Ledin, # M. Magnusson, * *Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Lund University Hospital, S-211 85 Lund, Sweden. epartment of Oto-Rhino-Laryngology, Head and Neck Surgery, Linköping University Hospital, S-581 85 Linköpng, Sweden.
Address of presenting author:	Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Lund University Hospital, S-211 85 Lund,Sweden.
E-mail:	anna.hafstrom@onh.lu.se
Phone:	046-171705
Fax:	046-2110968
Text of abstract:	Introduction. Visual control of postural sway was investigated to determine whether inadequate visual information or the readiness to receive visual information influence postural control and the adaptation of sagittal and lateral sway. Materials& methods. Torque was measured by a force-platform when stance was perturbed by bilateral vibratory stimulation to the calf muscles in 20 healthy subjects during six different visual conditions presented in a randomized order. Results. The least sway was found when standing with open eyes, a higher sway with a restricted visual field, and the highest sway values with closed eyes, open eyes in darkness, white light and looking at a light emitting diode in darkness. Having the eyes open in darkness at the beginning of perturbation caused an increase in sagittal and lateral sway compared to standing with closed eyes (p<0.05). The reduction of body sway by adaptation depended on the availability of visual information. There was an almost identical final level of body sway for the 4 tests where the subjects had no possibility of visual feedback to reduce sway i.e. closed eyes, open eyes in darkness, white opaque light and a light emitting diode in darkness. Conclusions. The results suggest that the influence of vision in postural control is more complicated than earlier has been assumed. We hypothesize that the higher sway standing with open eyes in darkness compared to with closed eyes could be explained by the individuals having their postural control programmed for reception of visual information and hence they did not initially increase the weighting of vestibular and proprioceptive input. This fits well with the hypotheses that the physical act of having the eyes opened or closed, in light or in darkness, would, in the early stages of postural adjustment, help select a postural program corresponding to the subject’s earlier experiences.
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Keywords:	Adaptation, balance, posturography, sway, vision

Created 2000-03-28