When an Object Appears Unexpectedly: Object Circumvention in Adults

Obstacles often appear unexpectedly in our pathway and these require us to make immediate adjustments. Despite how regularly we encounter such situations only few studies have considered how we adjust to unexpected obstacles in the pathway that require us to walk around them. The authors considered how adults adjust to the possibility of an obstacle appearing and then also how foot placement is adjusted to circumvent an obstacle. Fifteen healthy adults walked down an 11-m walkway, initially they were told this was a clear pathway and nothing in the environment would change (no gate), they then performed a series of trials in which a gate may (gate close) or may not (gate open) partially obstruct their pathway. The authors found that mediolateral trunk velocity and acceleration was significantly increased when there was the possibility of an obstacle but before the obstacle appeared. This demonstrates an adaptive walking strategy that seems to enable healthy young adults to successfully circumvent obstacles. The authors also categorized foot placement adjustments and found that adults favored making shorter and wider steps away from the obstacle. They suggest this combination of adjustments allows participants to maintain stability while successfully circumventing the obstacle.     

Examining Transfer Effects of Dual-Task Training Protocols for a Complex Locomotor Task

Training protocols designed to improve dual-task performance of an obstacle crossing and auditory Stroop task (OBS+Stroop) were tested. In Experiment 1, following baseline collection of OBS+Stroop trials, proximally related walking training was performed, and participants were then retested on the OBS+Stroop test. After training, participants adopted a more cautious obstacle crossing strategy, indicating a potentially safer navigation strategy. Transfer effects from distally related training were then examined (Experiment 2); a computer game training paradigm was examined using the same testing protocol as Experiment 1. Computer training demonstrated improved dual-task performance on some measures, but did not induce a more cautious stepping strategy. Results indicate that dual-task training needs to be similar to targeted tasks to yield reliable, positive training outcomes.     

Motor planning in Parkinson’s disease patients experiencing freezing of gait: The influence of cognitive load when approaching obstacles

Freezing of gait (FOG) in Parkinson’s disease (PD) is typically assumed to be a pure motor deficit, although it is important to consider how an abrupt loss of gait automaticity might be associated with an overloaded central resource capacity. If resource capacity limits are a factor underlying FOG, then obstacle crossing may be particularly sensitive to dual task effects in eliciting FOG. Participants performed a dual task (auditory digit monitoring) in order to increase cognitive load during obstacle crossing. Forty-two non-demented participants (14 PD patients with FOG, 13 PD who do not freeze, and 14 age-matched healthy control participants) were required to walk and step over a horizontal obstacle set at 15% of the participants’ height. Kinematic data were split into two phases of their approach: early (farthest away from the obstacle), and late (just prior to the obstacle). Interestingly, step length variability and step time variability increased when PD patients with FOG performed the dual task, but only in the late phase prior to the obstacle (i.e. when closest to the obstacle). Additionally, immediately after crossing, freezers landed the lead foot abnormally close to the obstacle regardless of dual task condition, and also contacted the obstacle more frequently (planning errors). Strength of the dual task effect was associated with low general cognitive status, declined executive function, and inappropriate spatial planning, but only in the PD-FOG group. This study is the first to demonstrate that cognitive load differentially impacts planning of the final steps needed to avoid an obstacle in PD patients with freezing, but not non-freezers or healthy controls, suggesting specific neural networks associated with FOG behaviours.     

Distraction Affects the Performance of Obstacle Avoidance During Walking

In this study, dual-task interference in obstacle-avoidance tasks during human walking was examined. Ten healthy young adults participated in the experiment. While they were walking on a treadmill, an obstacle suddenly fell on the treadmill in front of their left leg during either midswing, early stance, or late stance of the ipsilateral leg. Participants were instructed to avoid the obstacle, both as a single task and while they were concurrently performing a cognitive secondary task (dual task). Rates of failure, avoidance strategy, and a number of kinematic parameters were studied under both task conditions. When only a short response time was available, rates of failure on the avoidance task were larger during the dual task than during the single task. Smaller crossing swing velocities were found during the dual task as compared with those observed in the single task. The difference in crossing swing velocities was attributable to increased stiffness of the crossing swing limb. The results of the present study indicated that divided attention affects young and healthy individuals' obstacle-avoidance performance during walking.     

Boundary Distance Effects on Overshooting

Experiments with a subject-paced pursuit tracking task show that overshoot rate is dependent upon the distance between the target and the display boundary measured in the direction of movement, and that a previously noted inverse relationship with distance to the target is artifactual. The effect held for tasks with direct and reverse control-display relations, and for tasks with constant and variable target distances. The findings were consistent with Wetford’s (1968) hypothesis that a pursuit response is initiated with a ballistic, distance-covering, movement. Ralph Leonardo carried out extensive work in collecting data, Fred Hyde maintained the apparatus, and Georgie Green assisted in data analysis.     

脓毒症研究进展及启示

脓毒症(sepsis)是是当前外科ICU所面临的棘手难题.对感染和脓毒症的研究已成为外科学十分活跃的领域之一,所取得的进展已使人们从本质上更深刻、更准确地了解感染与脓毒症,从而为解决这一棘手问题开辟新的途径.脓毒症的研究揭示了人类科学发现和科学认识的普遍规律.     

Obstacle Avoidance Increases Asymmetry of Crossing Step in Individuals With Parkinson's Disease and Neurologically Healthy Individuals

The authors' aim was to investigate gait asymmetry of crossing step during obstacle avoidance while walking in people with Parkinson's disease (PD) under and without the effects of dopaminergic medication. Thirteen individuals with PD and 13 neurologically healthy individuals performed 5 trials of unobstructed gait and 10 trials of obstacle crossing during gait (5 trials with each leg) and spatiotemporal parameters were analyzed. Obstacle crossing increased step duration of the crossing step for the most-affected or nondominant limb compared to the crossing step with the least-affected or dominant limb. Individuals with PD without the effects of medication increased step duration for the step with the least-affected limb compared to the step with the most-affected limb during obstacle crossing.     

Saccade-Stepping Interactions Revise the Motor Plan for Obstacle Avoidance

The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of ?500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately ?300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.     

Obstacle Crossing Differences Between Blind and Blindfolded Subjects After Haptic Exploration

Little is known about the ability of blind people to cross obstacles after they have explored haptically their size and position. Long-term absence of vision may affect spatial cognition in the blind while their extensive experience with the use of haptic information for guidance may lead to compensation strategies. Seven blind and 7 sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed an obstacle after a haptic exploration. Blind and blindfolded subjects used different strategies to cross the obstacle. After the first 20 trials the blindfolded subjects reduced the distance between the foot and the obstacle at the toe-off instant, while the blind behaved as the subjects with full vision. Blind and blindfolded participants showed larger foot clearance than participants with vision. At foot landing the hip was more behind the foot in the blindfolded condition, while there were no differences between the blind and the vision conditions. For several parameters of the obstacle crossing task, blind people were more similar to subjects with full vision indicating that the blind subjects were able to compensate for the lack of vision.     

The Critical Point to Step into a Hole is Similar in Young and Older Adults

Abstract

The avoidance of a hole in the pathway while walking has been systematically investigated; however, depending on the dimensions of the hole, the option to avoid it is infeasible, and it is necessary to use the so-called accommodation strategy to step into the hole. We investigated the critical point between the avoidance and accommodation strategies when dealing with a hole in the ground during locomotion of young and older adults. Young and older adults performed two tasks: verbal estimation and walking. We used holes of different lengths and constant depth (12?cm). In the verbal estimation task, participants stood and looked at each hole and verbally respond if they would step into or avoid it. In the walking task, they walked and chose to either step or avoid the hole. Both age groups preferred to step into the hole when it was larger than 1.3 times their foot length in both tasks. The perception of affordances of young and older adults to step into a hole was similar, and it was unaffected by the investigated tasks. Thus, our participants preferred to have a safety margin that was large enough to guarantee that the whole foot would accommodate within the hole.