Evaluation of Reorientation Techniques and Distractors for Walking in Large Virtual Environments

Virtual Environments (VEs) that use a real-walking locomotion interface have typically been restricted in size to the area of the tracked lab space. Techniques proposed to lift this size constraint, enabling real walking in VEs that are larger than the tracked lab space, all require reorientation techniques (ROTs) in the worst-case situation–when a user is close to walking out of the tracked space. We propose a new ROT using visual and audial distractors–objects in the VE that the user focuses on while the VE rotates–and compare our method to current ROTs through three user studies. ROTs using distractors were preferred and ranked more natural by users. Users were also less aware of the rotating VE when ROTs with distractors were used. Our findings also suggest that improving visual realism and adding sound increased a user's feeling of presence

Trunk and lower extremity movement patterns, stress fracture risk factors, and biomarkers of bone turnover in military trainees

Context: Military service members commonly sustain lower extremity stress fractures (SFx). How SFx risk factors influence bone metabolism is unknown. Understanding how SFx risk factors influence bone metabolism may help to optimize risk-mitigation strategies. Objective: To determine how SFx risk factors influence bone metabolism. Design: Cross-sectional study. Setting: Military service academy. Patients or Other Participants: Forty-five men (agepre ¼ 18.56 6 1.39 years, heightpre ¼ 176.95 6 7.29 cm, masspre ¼ 77.20 6 9.40 kg; body mass indexpre ¼ 24.68 6 2.87) who completed Cadet Basic Training (CBT). Individuals with neurologic or metabolic disorders were excluded. Intervention(s): We assessed SFx risk factors (independent variables) with (1) the Landing Error Scoring System (LESS), (2) self-reported injury and physical activity questionnaires, and (3) physical fitness tests. We assessed bone biomarkers (dependent variables; procollagen type I amino-terminal propeptide [PINP] and cross-linked collagen telopeptide [CTx-1]) via serum. Main Outcome Measure(s): A markerless motion-capture system was used to analyze trunk and lower extremity biomechanics via the LESS. Serum samples were collected post-CBT; enzyme-linked immunosorbent assays determined PINP and CTx-1 concentrations, and PINP: CTx-1 ratios were calculated. Linear regression models demonstrated associations between SFx risk factors and PINP and CTx-1 concentrations and PINP: CTx-1 ratio. Biomarker concentration mean differences with 95% confidence intervals were calculated. Significance was set a priori using a ≤ .10 for simple and a ≤ .05 for multiple regression analyses. Results: The multiple regression models incorporating LESS and SFx risk factor data predicted the PINP concentration (R2 ¼ 0.47, P ¼ .02) and PINP: CTx-1 ratio (R2 ¼ 0.66, P ¼ .01). The PINP concentration was increased by foot internal rotation, trunk flexion, CBT injury, sit-up score, and pre- to post-CBT mass changes. The CTx-1 concentration was increased by heel-to-toe landing and post-CBT mass. The PINP: CTx-1 ratio was increased by foot internal rotation, lower extremity sagittal-plane displacement (inversely), CBT injury, sit-up score, and pre- to post-CBT mass changes. Conclusions: Stress fracture risk factors accounted for 66% of the PINP: CTx-1 ratio variability, a potential surrogate for bone health. Our findings provide insight into how SFx risk factors influence bone health. This information can help guide SFx risk-mitigation strategies

Automated quantification of the landing error scoring system with a markerless motion-Capture system

Context: The Landing Error Scoring System (LESS) can be used to identify individuals with an elevated risk of lower extremity injury. The limitation of the LESS is that raters identify movement errors from video replay, which is time-consuming and, therefore, may limit its use by clinicians. A markerless motion-capture system may be capable of automating LESS scoring, thereby removing this obstacle. Objective: To determine the reliability of an automated markerless motion-capture system for scoring the LESS. Design: Cross-sectional study. Setting: United States Military Academy. Patients or Other Participants: A total of 57 healthy, physically active individuals (47 men, 10 women; age ¼ 18.6 6 0.6 years, height ¼ 174.5 6 6.7 cm, mass ¼ 75.9 6 9.2 kg). Main Outcome Measure(s): Participants completed 3 jump-landing trials that were recorded by standard video cameras and a depth camera. Their movement quality was evaluated by expert LESS raters (standard video recording) using the LESS rubric and by software that automates LESS scoring (depth-camera data). We recorded an error for a LESS item if it was present on at least 2 of 3 jump-landing trials. We calculated j statistics, prevalence- and bias-adjusted j (PABAK) statistics, and percentage agreement for each LESS item. Interrater reliability was evaluated between the 2 expert rater scores and between a consensus expert score and the markerless motion-capture system score. Results: We observed reliability between the 2 expert LESS raters (average j ¼ 0.45 6 0.35, average PABAK ¼ 0.67 6 0.34; percentage agreement ¼ 0.83 6 0.17). The markerless motion-capture system had similar reliability with consensus expert scores (average j ¼ 0.48 6 0.40, average PABAK ¼ 0.71 6 0.27; percentage agreement ¼ 0.85 6 0.14). However, reliability was poor for 5 LESS items in both LESS score comparisons. Conclusions: A markerless motion-capture system had the same level of reliability as expert LESS raters, suggesting that an automated system can accurately assess movement. Therefore, clinicians can use the markerless motion-capture system to reliably score the LESS without being limited by the time requirements of manual LESS scoring

Beyond the Libet clock: modality variants for agency measurements

The Sense of Agency (SoA) refers to our capability to control our own actions and influence the world around us. Recent research in HCI has been exploring SoA to provide users an instinctive sense of “I did that” as opposed to “the system did that”. However, current agency measurements are limited. The Intentional Binding (IB) paradigm provides an implicit measure of the SoA. However, it is constrained by requiring high visual attention to a “Libet clock” onscreen. In this paper, we extend the timing stimulus through auditory and tactile cues. Our results demonstrate that audio timing through voice commands and haptic timing through tactile cues on the hand are alternative techniques to measure the SoA using the IB paradigm. They both address limitations of the traditional method (e.g., lack of engagement and visual demand). We discuss how our results can be applied to measure SoA in tasks involving different interactive scenarios common in HCI

Rafting in Antarctic Collembola

Darwin was an early exponent of the importance of ‘occasional means of dispersal’ in accounting for the present-day distribution of plants and animals. This study examined the implications of capture on the water surface of meltwater and seawater for the local and long-range dispersal of Antarctic springtails. Individuals of the maritime Antarctic collembolan Cryptopygus antarcticus, were floated on tap water and seawater at 0, 5 and 10°C. LT50s on seawater were 34 (10°C), 65 (5°C) and 75 (0°C) days. On tap water, LT50s were 69 (10°C), 126 (5°C) and 239 (0°C) days. Less than 20% escaped from the water surface. A significantly greater proportion of springtails moulted on tap water and viable offspring were produced on both tap water and seawater. Comparison across treatments of survival of moulting and non-moulting individuals found significantly greater survival in moulting animals for three of the treatment combinations. It is suggested that moult exuviae facilitate survival on the water film through the simultaneous provision of a flotation aid and a source of nourishment – that is, an ‘edible raft’. A separate experiment measuring changes in haemolymph osmolality over time on tap water and seawater at 2 and 5°C found significant differences in all treatments. Causes of mortality are discussed in relation to osmoregulatory failure and starvation

Virtual Reality: Principles and Applications

Virtual reality aims at immersing a user in a virtual environment. Dedicated virtual reality technologies of human–computer interaction enable to make the link between the user and a virtual environment in capturing the user’s motion, acting on his senses as well as computing the virtual experience in real-time. The immersion in virtual environment is evaluated through the user’s perception and reaction. Virtual reality is used in a large variety of application domains which need multisensory interaction and navigation facilities. Virtual prototyping is also used in the industry to improve design process