Papers by Jernej Čamernik
Human motor skill learning is driven by the necessity to adapt to new situations. While supportiv... more Human motor skill learning is driven by the necessity to adapt to new situations. While supportive contacts are essential for many tasks, little is known about their impact on motor learning. To study the effect of contacts an innovative full-body experimental paradigm was established. The task of the subjects was to reach for a distant target while postural stability could only be maintained by establishing an additional supportive hand contact. To examine adaptation, non-trivial postural perturbations of the subjects' support base were systematically introduced. A novel probabilistic trajectory model approach was employed to analyze the correlation between the motions of both arms and the trunk. We found that subjects adapted to the perturbations by establishing target dependent hand contacts. Moreover, we found that the trunk motion adapted significantly faster than the motion of the arms. However, the most striking finding was that observations of the initial phase of the left arm or trunk motion (100–400 ms) were sufficient to faithfully predict the complete movement of the right arm. Overall, our results suggest that the goal-directed arm movements determine the supportive arm motions and that the motion of heavy body parts adapts faster than the light arms. Most of our every day motor skills involve strict control of postural stability in parallel to the execution of the primary motor task. A great deal of these tasks also require additional supportive hand contacts beside the feet that are in contact with the ground. An example task is the reaching for a glass on the highest kitchen shelf when we typically have to use the other hand to support the body by leaning on the kitchen counter. To successfully perform such a reaching motion and to simultaneously ensure the postural stability, the motion of the body and both arms have to be perfectly synchronized and coordinated. Till now it is unclear how this coordination develops or adapts during skill learning. In general, supportive hand contacts increase the stability during balancing and complement humans' sophisticated motor abilities. Already light touch fingertip contacts provide sufficient feedback to enhance postural stability 1–4. Notable mechanical support is gained by holding onto a handrail, which enables humans to generate contact forces to better counteract perturbations 5,6. A notable exception to these static contacts studies are fall prevention experiments. It was shown that humans prefer reach-to-grasp strategies to rapid stepping with age 7,8. All these works underline the importance of contacts but cannot answer the posed question of how the coordination of supportive contacts and primary tasks develops or adapts. Like the ability to balance, the utilization of supportive hand contacts has to be learned 9,10. In the early childhood , learning of postural balance is tightly intertwined with supportive hand motion. At eight months infants already learn how to balance on hands and knees during crawling; at ten months they start walking with support from hanging on a table or a couch; and at about one year infants already know how to balance on two feet and walk independently across the room 11,12. While it is known that people develop optimal motor control strategies both for postural stability and manipulation 13–16 , it is unclear how these two distinctive motor tasks relate to each other and how their relationship affect the learning of novel motor skills or when re-establishing motor abilities in novel environments. A thorough understanding of these issues is of particular interest for the field of
When balance is exposed to perturbations, hand contacts are often used to assist postural control... more When balance is exposed to perturbations, hand contacts are often used to assist postural control. We investigated the immediate and the transitionary effects of supportive hand contacts during continuous anteroposterior perturbations of stance by automated waist-pulls. Ten young adults were perturbed for 5 min and required to maintain balance by holding to a stationary, shoulder-high handle and following its removal. Center of pressure (COP) displacement, hip, knee and ankle angles, leg and trunk muscle activity and handle contact forces were acquired. The analysis of results show that COP excursions are significantly smaller when the subjects utilize supportive hand contact and that the displacement of COP is strongly correlated to the perturbation force and significantly larger in the anterior than posterior direction. Regression analysis of hand forces revealed that subjects utilized the hand support significantly more during the posterior than anterior perturbations. Moreover, kinematical analysis showed that utilization of supportive hand contacts alter posture of the whole body and that postural readjustments after the release of the handle, occur at different time scales in the hip, knee and ankle joints. Overall, our findings show that supportive hand contacts are efficiently used for balance control during continuous postural perturbations and that utilization of a handle has significant immediate and transitionary effects on whole body posture.
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Papers by Jernej Čamernik