UBC Theses and Dissertations
Postural threat modulates human perceptions of balance-related movement Cleworth, Taylor William
Height-induced postural threat affects emotional state and upright feet-in-place standing balance behaviour during static, voluntary and dynamic tasks. Facing a threat to balance also affects sensory and cortical processes during balance tasks. As sensory and cognitive functions are crucial in forming perceptions of movement, balance-related changes during threatening conditions might be associated with changes in conscious perceptions. Therefore, the purpose of this thesis was to examine the changes and potential mechanisms underlying conscious perceptions of balance-relevant information during height-induced postural threat. A combination of five experimental procedures utilized height-induced postural threat to manipulate emotional state, balance behaviour, and/or conscious perceptions of sensory stimuli involved in balance. The first three studies assessed conscious perception of body position during static stance, voluntary leaning, and dynamic stance, respectively. During quasi-static balance, height-induced threat increased gain between actual and perceived movement as postural sway decreased in amplitude while perceived movement amplitude remained the same in the HIGH (3.2 m, at the edge) compared to LOW (1.1 m, away from edge) height condition. During voluntary leaning, perceived whole-body position in a voluntary leaning task was larger at height across ten different leaning positions (within the limits of stability). During continuous mediolateral pseudorandom support surface rotations, perceived movement of the trunk was larger while actual lateral movement of the upper trunk did not change in the HIGH compared to LOW height conditions. The continuity of results across these three studies illustrate height-induced postural threat increases the amplitude of perceived movement during balance tasks independent of behavioural changes. The final study included two experiments to determine how changes in somatosensory perceptual thresholds change with increased threat. Perceptual thresholds for ankle rotations were elevated while foot sole vibrations thresholds remained unchanged in the HIGH compared to LOW condition. These studies further our understanding of the relationship between emotional state, perceived risk, and balance performance. Taken together, postural threat can affect emotional state and conscious perceptions of balance-related movement. These results highlight the effect of postural threat influences on neurophysiological and cognitive components of balance control, and provide insight into clinical balance assessment and intervention.
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