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.     

Learning to Move

ABSTRACT— Locomotion—moving the body from place to place—is one of infants' greatest achievements. In addition to conquering gravity, infants must cope with variable and novel constraints on balance and propulsion. At the same time that they are learning to move, changes in infants' bodies, skills, and environments change the biomechanical constraints on movement. Recent work highlights both flexibility and specificity in infants' responses to novel and variable situations, demonstrating that infants are learning to learn as they master locomotion. Within sitting, crawling, cruising, and walking postures, experienced infants adapt their locomotor responses to the current biomechanical constraints on movement. However, what infants have learned about coping with variability and novelty in earlier-developing postures does not transfer to later-developing postures.     

脂多糖免疫激活导致抑郁性行为的动物研究：剂量和时程效应

“抑郁症细胞因子假说”的提出为抑郁障碍的病因学研究提供了一个新的方向,为了探讨脂多糖（lipopolyaccharide,LPS）诱导的免疫激活与抑郁性行为产生之间的关系,本研究采用50只SD大鼠随机分为五组LPS400,LPS200,LPS50,LPS10,LPS0,分别于实验期第0天和第3天注入LPS400ug/kg,,200ug/kg,50ug/kg,10ug/kg和生理盐水。以糖精水偏爱,旷场行为和高架十字迷宫评定大鼠LPS注射后2小时,24小时,48小时的行为变化。结果显示一次LPS注射后2小时,LPS50,LPS200,LPS400组动物与生理盐水组动物相比较,其糖精水偏爱分数（p<0.01）,旷场中的水平活动距离(p<0.01)和直立行为(p<0.01)以及高架十字迷宫中的闭合臂进入次数(p<0.01)和开放臂进入次数显著下降(p<0.01);重复注射后2小时LPS注射组动物的闭合臂进入次数显著降低（p<0.01）;但LPS10组与生理盐水组动物在行为上没有差异,50ug/kg,200ug/kg和400ug/kg剂量的各组之间没有差异。LPS注射后24小时和48小时以及重复注射后大鼠的行为没有发现显著变化。提示LPS诱导的免疫激活对抑郁行为产生有一定的作用。免疫激活的细胞因子能够导致动物出现明显的抑郁性行为,但是这种行为缺乏长时程效应,因此LPS诱导的抑郁障碍的动物模型应用是非常有限的。免疫激活的前炎性细胞因子可能是导致抑郁障碍产生的其中一个原因而不是唯一原因。     

Watch Where You're Going? Interferer Velocity and Visual Behavior Predicts Avoidance Strategy During Pedestrian Encounters

Pedestrians can avoid collisions with other pedestrians by modifying some combination of their velocity and their path. The authors investigated how path constraints (constrained or unconstrained), interferer velocity (slow or fast), and vision (looking or not looking; time spent looking at the interferer) influenced collision avoidance to an oblivious interferer walking on a perpendicular path. Ten participants walked 6 m to either a point or line target on either a constrained or unconstrained path while wearing an eye-tracking device and avoiding an oblivious interferer that walked at 2 speeds. Looking behavior and interferer velocity were reliable predictors of determining whether a pedestrian would pass in front of or behind the interferer, while path constraints were less reliable. These findings highlight the degeneracy in human movement systems and suggest that, in complex environments, behavior may not always be optimized for efficiency.     

Interlimb coordination in prosthetic walking: effects of asymmetry and walking velocity

The present study focuses on interlimb coordination in walking with an above-knee prosthesis using concepts and tools of dynamical systems theory (DST). Prosthetic walkers are an interesting group to investigate from this theory because their locomotory system is inherently asymmetric, while, according to DST, coordinative stability may be expected to be reduced as a function of the asymmetry of the oscillating components. Furthermore, previous work on locomotion motivated from DST has shown that the stability of interlimb coordination increases with walking velocity, leading to the additional expectation that the anticipated destabilizing effect of the prosthesis-induced asymmetry may be diminished at higher walking velocities. To examine these expectations, an experiment was conducted aimed at comparing interlimb coordination during treadmill walking between seven participants with an above-knee prosthesis and seven controls across a range of walking velocities. The observed gait patterns were analyzed in terms of standard gait measures (i.e., absolute and relative swing, stance and step times) and interlimb coordination measures (i.e., relative phase and frequency locking). As expected, the asymmetry brought about by the prosthesis led to a decrease in the stability of the coordination between the legs as compared to the control group, while coordinative stability increased with increasing walking velocity in both groups in the absence of a significant interaction. In addition, the 2:1 frequency coordination between arm and leg movements that is generally observed in healthy walkers at low walking velocities was absent in the prosthetic walkers. Collectively, these results suggest that both stability and adaptability of coordination are reduced in prosthetic walkers but may be enhanced by training them to walk at higher velocities.     

Walking in an environment of moving ground texture

The visual control of global body movements has mainly been studied in terms of the maintenance of balance. The present experiment examined the effect of moving visual surroundings on the speed of locomotion. A virtually boundless optical environment was generated by the projection of a dotted texture on the ground that was reflected on large vertical mirrors fixed along the walls of the room. Subjects' head velocity was recorded over a walking path of about 10 m along the projection surface. In the experimental sessions, the texture was animated and moved at different speeds in the same direction as the subject or in the opposite direction. In the control condition, the projected texture remained motionless and therefore appeared to pass by at the subjects' walking speed. The subjects' task was to maintain a constant walking speed as far as possible over the different conditions. Changes in walking speed give indications of how the processing of optical flow modulates locomotor activity.     

Rat gestation during space flight: Outcomes for dams and their offspring born after return to earth

Sprague-Dawley rats were studied to learn whether gestation in the near-zero gravity, high radiation environment of space impacts selected mammalian postnatal events. Ten rats spent days nine to twenty of pregnancy aboard the space shuttle orbiterAtlantis (STS-66). Their movement, was studied shortly after return to Earth; subsequently, several of their offspring were cross-fostered and examined through postnatal day 81 (P81) for whole body growth and somatic motor development. Values for the flight animals were compared to ground-based control groups. Relative to controls, the pregnant flight rats showed a marked paucity of locomotion during the first few hours after returning to Earth. There was greater likelihood of perinatal morbidity for the offspring of flight dams when compared to the control groups. Whole body weight of surviving offspring, averaged for each group separately, showed typical sigmoidal growth curves when plotted against postnatal age. The flight group for our study had a larger ratio of female to male pups, and that was sufficient to account for the lower average daily weight gained by the flight animals when compared to the control groups. Walking was universally achieved by P13 and preceded eye opening which was complete in all pups by P17. Thus, both of these developmental horizons were attained on schedule in the flight as well as the control rats. Characteristic changes were observed in hind limb step length and gait width as the pups grew. These patterns occurred at the same time in each group of rats. Therefore, prenatal space flight from days nine to twenty of gestation did not interfere with the establishment of normal patterns for hind paw placement during walking.     

When Walking Makes Perception Better

ABSTRACT— When we move, the visual world moves toward us. That is, self-motion normally produces visual signals (flow) that tell us about our own motion. But these signals are distorted by our motion: Visual flow actually appears slower while we are moving than it does when we are stationary and our surroundings move past us. Although for many years these kinds of distortions have been interpreted as a suppression of flow to promote the perception of a stable world, current research has shown that these shifts in perceived visual speed may have an important function in measuring our own self-motion. Specifically, by slowing down the apparent rate of visual flow during self-motion, our visual system is able to perceive differences between actual and expected flow more precisely. This is useful in the control of action.     

Task-specific modulations of locomotor action parameters based on on-line visual information during collision avoidance with moving objects

The objectives of this study were: (a) to determine if the control mechanism for interacting with a dynamic real environment is the same as in the virtual reality (VR) studies, and (b) to identify the action control parameters that are modulated to successfully pass through oscillating doors. The participants walked along a 14-m path towards oscillating doors (rate of change in aperture size = 44 cm/s and maximum aperture varied 70, 80, or 100 cm). The participants had to use vision to extrapolate what the aperture of the doors would be at the time of crossing and determine if a change in action parameters was necessary. If their current state did not match the required state then the participants made modifications to their actions. The results showed that individuals in a real environment used similar action modifications (i.e., velocity adjustments) as those seen in VR studies to increase success. Aside from the gradual velocity adjustments observed, there was an immergence of a different locomotor action parameter on some trials that was not seen in VR studies (i.e., shoulder rotations). These shoulder rotations occurred when the participants perceived that a velocity adjustment alone would not lead to a successful trial. These results show that participants use perception to control movement in a feedback rather than feedforward manner.     

Short-Term Effect of Crural Fasciotomy on Kinematic Variability and Propulsion During Level Locomotion

Treadmill locomotion can be characterized by consistent step-to-step kinematics despite the redundant degrees of freedom. The authors investigated the effect of disrupting the crural fascia in decerebrate cats to determine if the crural fascia contributed to kinematic variability and propulsion in the limb. Crural fasciotomy resulted in statistically significant decreases in velocity and acceleration in the joint angles during level walking, before, during, and after paw-off, particularly at the ankle. A further finding was an increase in variance of the limb segment trajectories in the frontal plane. The crural fascia therefore provides force transmission and reduction in kinematic variability to the limb during locomotion.