Title: The role of afferent vs. efferent signals to implicit sensorimotor adaptation
Supervisor: Dr. Romeo Chua
Committee members: Dr. Timothy Inglis, Dr. Hyosub Kim
Abstract: Humans continuously adjust their movements to adapt to changes in both external surroundings (e.g., walking on a slippery surface) or internal conditions (e.g., fatigue). Whereas we may be consciously aware of external changes as they are often sudden or obvious, internal changes are usually slow and gradual, provoking adaptation that can occur implicitly. Implicit adaptation broadly refers to the components of sensorimotor learning which we are not consciously aware of. The clamped visual feedback task has been developed to probe the implicit component of adaptation without contamination from explicit strategies. In this task, participants are instructed to reach towards targets on a visual display while observing cursor feedback representing hand position. Apparent visual errors are created by rotating visual feedback a constant angle away from the target. These visual errors create a difference between the visual feedback representing their hand and where they actually feel their hand. Moreover, where one feels their hand can be influenced by the misaligned visual feedback. This misperception in position sense has been proposed to induce motor adaptation.
In my project, I am investigating whether the misaligned visual feedback during the visual-motor rotation task shifts our perception of where our hand is by biasing where we feel it to be (the sensory input – proprioception) or where we expected our hand to be based on how our brain commanded our hand to move (motor output). This will be examined through an isometric aiming task. Instead of performing actual reaching movements, participants will be instructed to move a visual cursor towards various targets by applying a horizontal force to an immovable joystick. During baseline trials the cursor will move in the direction of their imposed force. During perturbation trials, the cursor will follow an invariant path rotated relative to the target. Participants will be instructed to ignore this task-irrelevant cursor feedback and continue to “reach” towards the target. By completing the task without actually moving, proprioceptive feedback becomes irrelevant because it is no longer coupled to the actual reach trajectory. By removing the relevance of proprioceptive feedback while making a motor command towards the target, we are better able to understand how each of these signals may be contributing to adaptation. The findings of this study will help expand theoretical understanding and provide empirical evidence for computational models seeking to describe implicit adaptation behaviour.