Perturbations to the upper limb in aiming tasks act to force individuals to modify their movements using online control processes. Individuals are able to successfully counteract these mechanical and perceptual perturbations to accurately acquire a specific target goal. What is less well understood is how individuals self-initiate a change to their trajectory during obstacle avoidance. A series of two studies were conducted to better understand the effects of a visual perturbation when performing two-dimensional sliding aiming movements during a manual obstacle avoidance task when a second set of obstacles appeared unexpectedly along the preferred, optimal trajectory. On each trial, a planned obstacle appeared at 25%, 50% or 75% of the movement amplitude. On some trials, a second set of obstacles appeared early or late in the movement to force participants to make online corrections or adapt their preferred trajectory to successfully reach the specified target. Results revealed that the mere possibility of the unexpected second obstacles influenced the overall trajectory and movement kinematics (i.e., whether that second obstacles appeared or not). Despite performing the movement in the same amount of time, participants executed a more lateral avoidance trajectory and reached higher accelerations later and further into the movement. We suggest that this pattern of behaviour is indicative of an optimal movement strategy such that the potential for an online correction resulted in individuals planning for the worst-case scenario. The presentation of a case-study for an individual with autism spectrum disorder (ASD) provides insight into potential differences in obstacle avoidance tasks when compared to a matched control. Despite relative differences in execution behaviour, the individual with an ASD successfully completed the task. This provides potential support for the sparing of motor execution processes within this population. Taken together, we suggest that optimal movement strategies may be better defined on a more individual basis. That is, what is optimal for one population might not be optimal for another. / Thesis / Master of Science (MSc) / It is well known that individuals are able to successfully aim to targets in environments that are both predictable and unpredictable. Additionally, these trajectories are successfully modified in the presence of an expected obstacle resulting in a change to the optimal movement to incorporate the location of the obstacle. What is less understood, however, is how individuals respond to the sudden onset of an obstacle along the optimal trajectory. This thesis characterizes these behaviours using a manual obstacle avoidance task wherein obstacles unexpectedly appear to obstruct the preferred movement pathway. The behavioural response to this perturbation is indicative of the performance of more cautious movements, adapted for the worst-case scenario. On average, individuals compromise between the biomechanical and computational demands of the task to execute wide trajectories that do not need to be updated during movement execution, a response that is potentially identified in an autism spectrum population.