Locomotor Adaptation versus Perceptual Adaptation when Stepping Over an Obstacle with a Height Illusion

Background During locomotion, vision is used to perceive environmental obstacles that could potentially threaten stability; locomotor action is then modified to avoid these obstacles. Various factors such as lighting and texture can make these environmental obstacles appear larger or smaller than their actual size. It is unclear if gait is adapted based on the actual or perceived height of these environmental obstacles. The purposes of this study were to determine if visually guided action is scaled to visual perception, and to determine if task experience influenced how action is scaled to perception. Methodology/Principal Findings Participants judged the height of two obstacles before and after stepping over each of them 50 times. An illusion made obstacle one appear larger than obstacle two, even though they were identical in size. The influence of task experience was examined by comparing the perception-action relationship during the first five obstacle crossings (1–5) with the last five obstacle crossings (46–50). In the first set of trials, obstacle one was perceived to be 2.0 cm larger than obstacle two and subjects stepped 2.7 cm higher over obstacle one. After walking over the obstacle 50 times, the toe elevation was not different between obstacles, but obstacle one was still perceived as 2.4 cm larger. Conclusions/Significance There was evidence of locomotor adaptation, but no evidence of perceptual adaptation with experience. These findings add to research that demonstrates that while the motor system can be influenced by perception, it can also operate independent of perception

The influence of perturbing the working surface during reaching and grasping in children with hemiplegic cerebral palsy

Purpose. To examine unimanual and bimanual reaching and grasping in children with hemiplegic cerebral palsy with particular emphasis on the nature and extent of interlimb coupling when the working surface is perturbed. Method. Nine children with hemiplegic cerebral palsy and 7 control children with no movement difficulties took part in the study. Children were asked to pick up a cube unimamually and bimanually when the surface it was placed on was either sloping away from the child (Experiment 1) or towards the child (Experiment 2). Both 3D kinematic data and video data were gathered and qualitative descriptions of video data were made. Results. The working surface did indeed influence the nature and extent of interlimb coupling and this varied from participant to participant. Analysis of the displacement data revealed that during the bimanual condition lower trajectories were produced by both the hemiplegic and non hemiplegic sides, especially in Experiment 2. The control group showed little difference between the unimanual and bimanual condition. Conclusions. Evidence of interlimb coupling is found, these studies support the findings of our previous work that indicates that there are some benefits to performing bimanual movements in children with hemiplegic cerebral palsy