The Aging Effects And The Underlying Mechanisms On Action Control And Eye-hand Coordination

Action is the most important means for human to interact with the external world and the interaction between vision and motor control is most critical.Individuals perceive a lot of information from the surroundings and interact with the environment through central processing,action execution and visual feedback.It is well known that aging results in decrements in sensory system,cognitive system and motor system.In previous literature,the decrements of these systems are usually studied separately,so that it is yet to be clarified how aging effects the interaction between perception and action.The influences of aging on action control planned motor excecution and online visuomotor control need further investigation.In addition,the successful action control requires individuals to regain the balance through adaptation after the environmental change(e.g.the change of vision-action mapping).It is unknown whether there are aging effects on visuomotor adaptation and eye-hand coordination when vision-action mapping is distorted.Consequently,understanding why action control decline is critically important to elucidating how aging processes effect the vision-action integration and to the development of intervention programs aimed at reducing or even reversing the typical declines in action control.This study manages to help the elderly adapt to the influence of aging on the vision-action interaction.Based on the planning and control model,two types of actions are studied,namely,planned action and on-line visuomotor control.Here,we managed to systematically investigate 1)the aging tendency,and 2)the expected planning,which is based on the top-down information processing,and 3)the visual feedback,which is based on the bottom-up information processing,and 4)to explore how aging affected eye-hand coordination during these types of action control.A series of seven experiments were reported in this thesis.Experiments were conducted with crosssectional designs.100 elderly subjects(56-82 years old)and 20 young subjects(19-27 years old)as control group voluntarily participated in this study.They performed manual aiming or tracking movements on the surface of a digitizer.For the effect of age on eye-hand coordination,32 elderly subjects(60-73 years old)and the young control group(Experiment 3: n = 26,19-28 years old;experiment 7: n = 24,19-28 years old)were recruited,and the subjects' action and eye movements were recorded by digitizer and eye tracker.Study 1(Experiments 1-3)was to investigate the influences of aging on action planning and the eye-hand coordination during the action execution:Experiment 1 used the manual aiming task and demonstrated that regardless of target distance,the movement speed decreased,but the movement accuracy had no significant change with aging.Experiments 2 and 3 adopted a trial-by-trial planning aiming task,with 30°-rotation(cursor relative to hand)perturbation,which could induce visuomotor adaptation.The experiment revealed that with aging,there was a significant correlation between action planning and adaptability,but movement time did not change with aging significantly.Moreover,the performance of digital symbol task and block design task was related to both planning and adaptation,but the performance of Stroop task was only related to planning.In Experiment 3,closed-loop visual feedback was used to study the age effect of visuomotor adaptation,and there were no differences in the adaptability of subjects with different types of fixation.Study 2(Experiments 4-7)was to investigate the age effect on on-line control manual tracking and the eye-hand coordination during the control:Experiment 4 adapted the on-line control manual tracking task and found that the performance and stability of manual tracking became worse with advancing age and elderly prefered to taking smaller corrective actions.Then we investigated the age effects on visual reference task(Experiment 4),visuomotor manipulation task(Experiment 5)with veridical mapping,and the effect on visual reference task in the mirror mapping conditions(Experiment 6),respectively.Both visual reference and visual manipulation task could improve the performance of manual tracking for elderly,but it only happened under veridical mapping condition.The stability of the manual tracking for elderly was found even worse than without visual reference under mirror mapping condition.Experiment 7 injected an additional 200 ms artificial feedback delay to manual tracking task with visual reference,and there was no significant difference in eye-hand coordination between the two groups in the phase of adaptation.Compared with the young group,pursuit eye movements of elderly group were closer to the moving target while cursor lagged farther.Considering the results of Study 1 and Study 2,we draw the conclusion that even if the perception and action did not decrease significantly,there was still a significant decline in action control based on visual information.Cognitive processing and action planning had the same decay trend and might share common neural mechanism,while the performance of online visuomotor control maintained stability.The deficit of the predictive planning abilty of elderly was the main reason why elderly's adaptability decreased in action control.In addition,visual feedback could also affect the performance of action cotrol.However,eye-hand coordination was not damaged during adaptation.