Title: “Balance related perceptions of movement: The influence of height-induced postural threat”
Supervisor: Dr. Mark Carpenter (Kinesiology)
Committee Members: Dr. J. Timothy Inglis (Kinesiology), Dr. Romeo Chua (Kinesiology)
Abstract: Falls are a major concern in the health care community, and fear of falling is known to increase the risk of a fall. In young healthy adults, exposure to threatening environments can allow experimenters to explore the direct influence emotional state has on balance. Standing at the edge of an elevated surface has been shown to change balance behaviour, thought to reflect a stiffening strategy, with increased frequency and decreased amplitude of sway. In addition, sensory and cortical function are modulated when standing at height, as shown by increased proprioceptive sensitivity and vestibular reflex gain, as well as changes in cognitive processing and cortical activation. As sensory and cognitive functions are crucial in forming perceptions of movement, balance related changes during threatening conditions may be associated with changes in conscious perceptions. Therefore, the purpose of this thesis is to examine the changes in conscious perceptions of balance relevant information during postural threat. Five studies will be used to assess how whole body movement perceptions and individual sensory system perceptions are influenced by threat. Study one through three will be used to examine the conscious perception of body position during static stance, voluntary leaning, and dynamic stance. In the static and dynamic stance, individuals will track their sway using hand held tracking devices, whereas perception of voluntary leaning will be assessed by subjective reports of body position. Two final studies will be used to probe individual sensory systems thought to drive the changes in behaviour and perception associated with threat. First, proprioceptive perceptions of ankle rotations and foot sole skin vibrations will be assessed during standing. Finally, vestibular sensitivity will be assessed using galvanic vestibular stimulation. The results of these studies will be used to further our understanding of how fear and/or anxiety can directly influence standing balance, and assist in explaining some of the behaviours typically associated with a fear of falling.