The ability of young and elderly adults to keep a stable upright posture while facing changes in the availability of visual and/or propriomuscular information was investigated. The two sensory sources of information were alternatively available and withdrawn, jointly and separately, during 10-s alternating sequences. Vision was modified by means of liquid-crystal goggles, and proprioception was altered by means of tendon vibration of both antagonistic ankle muscles. Elderly adults were less stable than young adults when vision was withdrawn. Both groups were greatly affected when propriomuscular inputs were altered by vibration. Under constant visual conditions and following a propriomuscular perturbation (i.e., vibration), elderly adults were unable to take advantage of the reinsertion of propriomuscular inputs. They showed a transient, decreased stability and were unable to fully recover during a 10-s period, whereas young adults were able to rapidly integrate the information to stabilize their posture. When both propriomuscular and visual inputs were withdrawn and concurrently reinserted, the elderly adults did not show a transitory increase in the velocity of the center of foot pressure. The present results extend findings on the inability of elderly adults to reconfigure rapidly the postural set following reinsertion of sensory inputs. The results also suggest that elderly adults have difficulties in taking advantage of sensory redundancy in postural control.

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This study addresses the question of whether peripheral vision is involved in the control of hand trajectory direction during an aiming task performed at high speed. Ten adult subjects were required to aim at targets in various positions by making a punching movement with their hand. The experimental conditions were varied so that different parts of hand trajectory could be seen in the peripheral field. Two movement times were applied: < 130 msec, and 250-300 msec. The results indicate that a directional correction of trajectory can be made by means of on-line peripheral feedback, even with movements as brief as 110 msec.

The aim of the experiment was to study the adaptive capacities of children to perform drawing movements while being visually perturbed. Children aged 5-11 years and a group of adults drew diamonds via information provided through a computer screen. The screen display was either upright or rotated 180 degrees. Results showed that the absence of direct vision of the hand yielded more perturbation in the youngest group of children compared to all other groups. In spite of some initial difficulty, all children reached accurate control after five trials. When faced with spatial rotations of the visual field, youngsters were again more perturbed than others. All children showed the same rate of adaptation to visual rotations, but they differed on adaptive strategies. Five- and 7-year-olds shifted to a feedforward mode of control consisting of the production of a rapid gesture, followed by error evaluation in order to correct their next movement. Older children were characterised by a progressive integration of reafferent visual and proprioceptive information. It resulted in an increase in duration of strokes and reduced speed, meaning enhanced on-line retrieval of information. However, 9-year-old children experienced more difficulty recuperating sensory information during movement than 11-year-olds, and kept using error feedback. Finally, visuomanual coordination in children aged 11 years, while slightly differing from that of adults, was not yet totally mature.