Effects of multi-obstacle contexts on obstacle negotiation strategies in healthy older adults under dual-task conditions.

BACKGROUND: Performance of obstacle crossing is an attentionally demanding task due to the need for motor planning and gait regulation, particularly among older adults. Despite extensive studies on age-associated changes in obstacle negotiation strategies, relatively little is known about adaptive mechanisms in the elderly regarding multiple obstacle crossings with different execution demands. RESEARCH QUESTION: For better understanding of avoidance strategies employed by the elderly, the current study investigated adaptive mechanisms related to planning and implementation of more complex multi-obstacle contexts. Do older adults use a more conservative strategy such as prolonged step duration or elevated foot height when crossing obstacles with increased task demands of obstacle negotiation? METHODS: Eleven healthy older and 11 young adults participated in the experiment. We examined how the presence and physical property of the second obstacle influenced the planning and adjustments for obstacle avoidance performance. Spatiotemporal characteristics of the stepping movement were analyzed using a 3D motion capture system. RESULTS: Older adults showed a longer stance time before crossing the first obstacle than young adults when the task complexity increased. These stepping characteristics were more evident in the dual-task condition. However, their foot clearance and crossing speed were not influenced by the level of task complexity. SIGNIFICANCE: These findings suggest that healthy elderly participants may have difficulty in developing the motor plan rather than implementing the stepping strategies under more complex obstacle constraints. A general cognitive decline with advancing age or adaptation of compensatory adjustment to enhance postural stability may underlie such altered obstacle negotiation behaviors in older adults.

Compensatory postural responses to backward loss of balance in patients with cerebellar disease.

BACKGROUND: Impaired control of balance and coordinated reactions are a primary deficit of cerebellar dysfunction. As compared to other neurological patients with balance impairments, there has been little research assessing the characteristics of compensatory responses associated with falls in patients with cerebellar disease (CD). RESEARCH QUESTION: The aim of this study was to examine the effects of cerebellar disease on compensatory balance control in response to postural perturbation. Do CD patients increase the number of steps when responding to instability because of inappropriate initial step reactions or poor control of trunk motion or both? METHODS: In this explorative study, 10 patients suffering from degenerative cerebellar ataxia and 10 age-matched healthy controls were examined. The balance recovery reactions were assessed using a lean-and-release postural perturbation method. Spatiotemporal characteristics of stepping movement and COM variables associated with torso motion were analyzed using 3D motion capture system. RESULTS: CD patients took multiple steps whereas matched controls generally took single steps to recover balance following perturbation. The characteristics of the initial step at the time of the fall revealed that foot reaction time, foot response time, and step distance of the initial step were similar between CD patients and matched controls. However, CD patients exhibited a shorter foot-to-COM distance, higher COM velocity, and less trunk flexion with which to attenuate their body momentum after the landing of the first step than did matched controls. SIGNIFICANCE: Although initial step responses were probably adequate, poor control of torso motion appears to be a particular problem that causes multiple-step reactions in CD patients. This observation would help to guide the development of tailored fall intervention strategies in CD patients aimed at promoting their recovery capacity in response to a pronounced balance challenge.

The Development of Infants' Sensitivity to Behavioral Intentions when Inferring Others' Social Preferences.

The present study investigated whether infants reason about others' social preferences based on the intentions of others' interactive actions. In Experiment 1, 12-month-old infants were familiarized with an event in which an agent either successfully helped a circle to climb up a hill (successful-helping condition) or failed to help the circle to achieve its goal (failed-helping condition). During the test, the infants saw the circle approach either the helper (approach-helper event) or the hinderer (approach-hinderer event). In the successful-helping condition, the 12-month-old infants looked for longer at the approach-hinderer event than at the approach-helper event, but in the failed-helping condition, looking times were about equal for the two test events. These results suggest that 12-month-old infants could not infer the circle's preference when the helper's action did not lead to its intended outcome. In Experiment 2, 16-month-olds were tested in the failed-helping condition; they looked longer at the approach-hinderer event than at the approach-helper event, which suggests that they could reason about the third party's social preferences based on the exhibited intentions. In Experiment 3, 12-month-olds were familiarized with events in which the final outcomes of helping and hindering actions were ambiguous. The results revealed that 12-month-old infants are also sensitive to intentions when inferring other's social preferences. The results suggest that by 12-months of age, infants expect an agent to prefer and approach another who intends to help the circle to achieve its goal, regardless of the outcome. The current research has implications for moral reasoning and social evaluation in infancy.