Cautious gait in relation to knowledge and vision of height: is altered visual information the dominant influence?

For some people, visual exposure creates difficulty with movement and balance, yet the mechanisms causing this are poorly understood. The altered visual environment is an obvious possible cause of degraded balance. We studied locomotion in normal healthy adults along a 22-cm-wide walkway at ground level and at a height of 3.5 m. This produced substantial changes in gait progression (velocity reduced by 0.34 ms(-1), P <0.01), proportion of time spent in double support more than doubled (P <0.01), and galvanic skin conductance, a measure of physiological arousal, increased significantly (P <0.01). Since increasing visual distance is known to destabilize balance, our primary question was whether the disturbing effects of height could be eliminated by replacing sight of the drop with a visual surround comparable to ground level while retaining the danger and knowledge of the risk. Removing visual exposure did not significantly change the gait progression (P = 0.65) or double support duration (P = 0.58) but produced a small, significant reduction in physiological arousal (P = 0.04). In response to postural threat, knowledge of danger rather than current visual environment was the dominant cause of cautious gait and elevated physiological arousal in response to postural threat. We conclude that the mechanisms disturbing locomotion, balance, and autonomic response occur at a high task level which integrates cognition and prior experience with sensory input.