Nonlinear analysis of the effects of vision and postural threat on upright stance

The ability to control and maintain upright stance is crucial for humans to interact with their surroundings, allowing humans to navigate through environments. Behaviour during upright stance was examined using nonlinear methods to provide additional insight into postural threat (height) effects on postural control. Linear methods fail to address the nonstationary behaviour of the human body, while a nonlinear approach considers the underlying dynamics of postural sway.

Linear measures identified increases in amplitude at 3.2 m (HIGH) compared to ground level (LOW), but no change with eyes closed (EC). Nonlinear measures identified decreases in all recurrence quantification analysis (RQA) variables in the HIGH and EC condition. The changes in sway dynamics might represent increased randomness and adaptability in response to increased fear (HIGH) or decreased sensory information (EC). This study demonstrates how including an RQA could provide a more informative analysis than linear measures alone.