Abstract
Perturbations to the upper limb in aiming tasks act to force individuals to modify their movements using on-line control processes. Studies show that individuals are able to successfully counteract these mechanical (e.g. Nashed et al., 2014) and perceptual perturbations (e.g. Elliott et al., 1995) to accurately acquire a specific target goal. A series of two studies were conducted to better understand the effects of a perceptual perturbation when performing two-dimensional sliding movements during a manual obstacle avoidance task when a second obstacle appeared unexpectedly within a preferred aiming path. On each trial, an obstacle appeared at 25%, 50% or 75% of the movement amplitude. On some trials, a second set of obstacles appeared early or later in the movement that forced participants to make on-line corrections or adapt their preferred trajectory to successfully reach the specified target. Results revealed that the possibility of the unexpected second obstacle influenced the overall trajectory and movement kinematics (i.e., whether that second obstacle appeared or not). Specifically, participants executed a more lateral avoidance trajectory and reached higher peak velocities and accelerations.. When the onset of the secondary set of obstacles occurred later into the movement, it resulted in individuals reaching peak velocities later in their movement which indicated that the possibility of a secondary perturbation resulted in more cautious movements. Results will be further discussed in the context of obstacle avoidance and movement planning behaviours as well as possible modifications to these behaviours in individuals with an Autism Spectrum Disorder.
