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The Effect of Visual Stimuli on Postural Control in Standing Humans
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- Author / Creator
- Hemakumara, Sisuri G
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Balance is crucial for upright stance and mobility, with the control of balance being fundamental to most daily activities including rising from bed and walking. Upright bipedal stance is inherently unstable as the majority of the body’s mass is elevated high above the feet, creating instability and giving rise to a natural sway pattern. Balance control is a complex process involving sensorimotor systems, including the visual, vestibular, and somatosensory systems. Specifically, visual feedback has been demonstrated to be a potent sensory cue as the absence of vision leads to increased postural sway, while motion of the visual surround induces compensatory sway. We hypothesized that a rapid, transient, visual stimulus, akin to the motion parallax relayed during a push or slip, would evoke a rapid balance corrective reaction in the direction of the visual stimulus. Moreover, we hypothesized that the reaction would habituate with repeated exposure and provision of a stable light touch reference would stabilize or mitigate the balance reactions. Forty participants received 10 small, transient, visual displacements using the “moving room” paradigm. Visual stimuli were 2.5 cm in amplitude with a peak velocity of 124 mm/s. Twenty participants received forward visual displacements and the other twenty participants received backward visual displacement. In addition, half the participants received a stable light touch reference. Following the first visual stimulus 39 out of the 40 participants leaned in the direction of the visual stimulus, as demonstrated by a shift in the position of the center of pressure. However, the latency of the response was slow and unlikely to be a rapid balance reaction. Upon repeated exposure to the stimulus participants continued to lean in the direction the stimulus. The participants that received a stable light touch reference during the visual displacements also demonstrated a lean in the direction of the visual stimulus, although with smaller amplitudes. These results suggest that the slow latency postural leans exhibited by the participants are not balance reactions, but rather likely represent a postural reorientation of the body to realign with the new position of the visual surround. We suggest that this postural reorientation serves to reposition the head within the relocated spatial frame of reference of the visual surround. Further, the continued repositioning behaviour with repeated exposure and with the provision of light touch suggests that vision is a potent sensory cue in maintaining postural orientation.
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- Graduation date
- Fall 2024
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.