Browsing by Author "Miller, Ryan"

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    Modulation of Upper Limb Sensorimotor Control in Unpredictable Mechanical Environments
    (2021-12-16) Miller, Ryan; Cluff, Tyler; Aboodarda, Saied; Ryan, Peters
    Humans have the ability to adapt their movements to accommodate changes within the environment. A common strategy used to probe for adaptation is to expose people to environments where they will encounter predictable disturbances. We know comparatively little about whether people adapt to environments that are highly unpredictable, or how repeated exposure to unpredictable environments alters responses on larger time scales. This is important as many of our movements are performed in the presence of unpredictability. A basketball player with a clear lane to the hoop may alter their strategy if a defender steps in their way. The defender in this situation introduces unpredictability into the environment and the forward must adapt to achieve their task goal. In this thesis, I examine how people alter their electrophysiological, metabolic, and behavioural responses when exposed to unpredictable mechanical perturbations during upper limb posture control and reaching movements. In Chapter 3, I describe two experiments where 35 healthy participants maintained hand position within a fixed target while exposed to elbow perturbations that were unpredictable in direction. The results indicate that although the perturbations were unpredictable in direction, subjects produced stereotypical adaptation responses such as a reduction in muscle activity and energy expenditure, and an improvement in performance. Posture and reaching may involve distinct control mechanisms. In Chapter 4, 37 healthy subjects performed point-to-point reaching experiments while unpredictable perturbations were delivered during the reaching movement. The results in Chapter 4 demonstrated that humans produce adaptive responses to unpredictable perturbations during reaching, and such responses scale linearly to the amplitude of perturbation. Taken together, this work elucidates the plasticity of the nervous system and indicates that the nervous system works to minimize energy expenditure while maintaining the goals of motor control tasks.