THE EFFECTS OF AN UNEXPECTED VISUAL PERTURBATION ON HAND PATH TRAJECTORIES IN MANUAL OBSTACLE AVOIDANCE

Abstract

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.