Effects of Initial Starting Distance and Gap Characteristics on Children's and Young Adults' Velocity Regulation When Intercepting Moving Gaps.

OBJECTIVE: This study investigated how children and young adults regulate their velocity when crossing roads under varying traffic conditions. BACKGROUND: To cross roads safely, pedestrians must adapt their movements to the moving vehicles around them while tightly coupling their movement to visual information. METHOD: Using an Oculus Rift, 16 children and 16 young adults walked on a treadmill and intercepted gaps between two simulated moving vehicles in an immersive virtual environment. We varied the participants' initial distance from the curb to the interception point, as well as gap characteristics, including gap size and vehicle size. RESULTS: Varying the initial distance led to systematic adjustments in participants' approach velocities. The inter-vehicle gap and the vehicle size affected the crossing position induced by the initial distance. However, participants did not systematically scale their positions according to the initial distance in narrow gap. Notably, children did not finely tune their movements when they approached wide gap from a closer distance or when they approached the large vehicle from closer distance. CONCLUSION: Children were less precise in coupling their movements to the moving vehicle in complex traffic environments. In particular, large moving vehicles approaching at closer distances can pose risks when children cross roads. APPLICATION: These findings suggest the need for an intervention program to improve children's skill in perceiving larger vehicles and timing their movements when crossing roads. We suggest using an interactive virtual reality system to practice this skill.

The influence of kayaking and rowing sports experience on postural response to optic flow.

This study investigated the postural response of kayakers and rowers to imposed optic flow. The athletes, with experience in unstable water environments, should have a specific postural response to optic flow. 12 male participants with kayaking and rowing experience and 12 with no specific sports experience were asked to stand still with and without room motion. This study varied the amplitude and frequency of room motion and evaluated the trajectory of the center of pressure. The kayaking and rowing group were less influenced by imposed optic flow, and body sway was more closely synchronized to the oscillating room compared to the Non-athlete group. These results suggest that postural adaptation occurs in association with experience in kayaking and rowing.

A least action principle for interceptive walking.

The principle of least effort has been widely used to explain phenomena related to human behavior ranging from topics in language to those in social systems. It has precedence in the principle of least action from the Lagrangian formulation of classical mechanics. In this study, we present a model for interceptive human walking based on the least action principle. Taking inspiration from Lagrangian mechanics, a Lagrangian is defined as effort minus security, with two different specific mathematical forms. The resulting Euler-Lagrange equations are then solved to obtain the equations of motion. The model is validated using experimental data from a virtual reality crossing simulation with human participants. We thus conclude that the least action principle provides a useful tool in the study of interceptive walking.

Using a Virtual Reality Walking Simulator to Investigate Pedestrian Behavior.

To cross a road successfully, individuals must coordinate their movements with moving vehicles. This paper describes use of a walking simulator in which people walk on a treadmill to intercept gaps between two moving vehicles in an immersive virtual environment. Virtual reality allows for a safe and ecologically varied investigation of gap crossing behavior. Manipulating the initial starting distance can further the understanding of a participant's speed regulation while approaching a gap. The speed profile may be assessed for various gap crossing variables, such as initial distance, vehicle size, and gap size. Each walking simulation results in a position/time series that can inform how velocity is adjusted differently depending on the gap characteristics. This methodology can be used by researchers investigating pedestrian behavior and behavioral dynamics while employing human participants in a safe and realistic setting.

Clinical significance of minimal change lesions of the esophagus in a healthy Korean population: a nationwide multi-center prospective study.

BACKGROUND AND AIM: At least half of the patients with typical reflux symptoms have non-erosive reflux disease (NERD). Minimal change lesions are commonly seen in the screening endoscopic examinations for individuals without clinically significant symptoms. We evaluated the correlation between minimal changes and symptoms in individuals visiting the hospital for routine health check-up by a nationwide survey in 2006. METHODS: Upper gastrointestinal endoscopic examinations as a health check-up were performed for 25,536 patients. Among them, symptom questionnaires were given in 23,350 patients without mucosal break or Barrett's esophagus. Endoscopic findings of the lower esophagus were divided into normal or minimal changes. Minimal changes in the present study included white turbid discoloration and Z-line blurring. RESULTS: Among a total of 25,536 subjects, reflux esophagitis was found in 2019 subjects (7.91%) and 3043 patients (11.9%) were classified as having minimal changes. History of gastroesophageal reflux disease (GERD) was more commonly found in individuals with minimal changes. Among the reflux-related symptoms, heartburn, acid regurgitation, globus sensation, and epigastric soreness were related to the minimal changes of the esophagus. Especially, individuals with globus sensation or epigastric soreness were more likely to have minimal changes compared to individuals without respective symptoms. Male gender, current smoker, history of H. pylori eradication, frequent stooping at work, hiatal hernia, and atrophic/metaplastic gastritis were found to be risk factors for minimal changes. CONCLUSION: The minimal changes were closely related with upper gastrointestinal symptoms and had similar risk factors for GERD, suggesting that minimal changes could be considered as early endoscopic findings of GERD.

Standing body sway in women with and without morning sickness in pregnancy.

Morning sickness typically is attributed to hormonal changes in pregnancy. We asked whether morning sickness is associated with changes in standing postural equilibrium, as occurs in research on visually induced motion sickness. Twenty-one pregnant women (mean age=30 years, mean height=163cm; mean weight=63kg) were tested during the first trimester. Laboratory-based balance measures were collected, along with perceived postural stability, the presence of morning sickness, and the severity of subjective symptoms. We varied the distance between the feet and the visual task performed during stance. Participants were classified as either experiencing (Sick, n=12) or not experiencing (Well, n=9) morning sickness. Perceived balance stability was lower for Sick than for Well women. The positional variability of sway was reduced for the Sick group, relative to the Well group. Positional variability decreased with wider stance width, and was reduced during performance of a more demanding visual task. Stance width and visual task also influenced the temporal dynamics of sway. Effects of stance width and visual task on postural sway were similar to effects in non-pregnant adults, suggesting that sensitive tuning of posture is maintained during the first trimester. The findings suggest that women with morning sickness may attempt to stabilize their bodies by reducing overall body sway. It may be useful to recommend that women adopt wider stance early in pregnancy.

Postural responses to a moving room in children with and without developmental coordination disorder.

Children (10 or 11 years old) with and without developmental coordination disorder (DCD) were exposed to imposed optic flow in a moving room. We manipulated the amplitude and frequency of oscillatory room motion, and we evaluated the coupling of standing body sway with room oscillations. The results revealed that standing sway of both children with and without DCD was influenced by room motion. However, children with DCD responded differently than children without DCD to specific combinations of room motion amplitude and frequency. We conclude that DCD can influence a child's use of imposed optic flow for postural control and that these effects are situation-specific rather than being systemic.