The Effect of Age, Cognition and Context on Human Responses to Tendon Vibration
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High-frequency vibration applied to the musculotendinous junction of a joint induces an illusory perception of the stimulated joint’s position. Historically, the illusory perception of movement during tendon vibration was described as a certain outcome, but more recently has been reportedly difficult to elicit in many instances. This poses problems for researchers who have expressed interest in manipulating human responses to tendon vibration for the purpose of neurorehabilitation. The purpose of this dissertation was to investigate factors that may influence the perception of the movement illusions induced by tendon vibration.The first experiment examined the influence of one’s knowledge and expectations about the illusion, as well as, whether directing attention to or away from the tendon vibration stimulation influenced the magnitude of movement illusions experienced. Providing instructions about the expected direction of movement illusions during tendon vibration, irrespective of their accuracy, reduced the magnitude of movement illusions perceived. Directing the attention to the external aspects of the joint positioning task, reduced the magnitude of the illusions the greatest extent, while the addition of a 1-back cognitive task meant to dilute attention resources was not challenging enough to alter the movement illusions perceived.The second experiment compared movement illusions induced by tendon vibration in a group of young and older adults. Participants experienced tendon vibration while performing both a continuous and discrete contralateral matching task, at both the elbow and knee, on both sides of the body. Older adults experienced a larger magnitude of movement illusions at the elbow and in the continuous contralateral matching task, while no differences between young and old were observed in the discrete matching task, at the knee or between the left and right limbs. A positive correlation was observed in movement illusions experienced between the continuous and discrete matching tasks, and between the left and right side of the body. In the second experiment, we also observed a weak but positive correlation between motor imagery ability and the magnitude of movement illusions perceived in the continuous contralateral matching task and at the elbow. Together, these outcomes suggest that the perception of movement illusions during tendon vibration results from the integration of both central and peripheral neural processes. Instructions about the illusions and the task can bias the outcome of experiments regarding tendon vibration and researchers should carefully consider their instructions and maintain consistency across participants and conditions. Elderly individuals and those who experience more vivid motor imagery experience greater movement illusions during tendon vibration stimulation, although the duration and location of stimulation would also influence the extent to which someone would experience movement illusions. These factors may be used to improve future investigations into human responses to tendon vibration. Future investigations should examine movement illusions in additional joints and a broader age range of participants before using these factors to identify individuals for the use of tendon vibration in neurorehabilitation.