Differential effects of head-mounted displays on visual performance

Head-mounted displays (HMDs) virtually augment the visual world to aid visual task completion. Three types of HMDs were compared [look around (LA); optical see-through with organic light emitting diodes and virtual retinal display] to determine whether LA, leaving the observer functionally monocular, is inferior. Response times and error rates were determined for a combined visual search and Go-NoGo task. The costs of switching between displays were assessed separately. Finally, HMD effects on basic visual functions were quantified. Effects of HMDs on visual search and Go-NoGo task were small, but for LA display-switching costs for the Go-NoGo-task the effects were pronounced. Basic visual functions were most affected for LA (reduced visual acuity and visual field sensitivity, inaccurate vergence movements and absent stereo-vision). LA involved comparatively high switching costs for the Go-NoGo task, which might indicate reduced processing of external control cues. Reduced basic visual functions are a likely cause of this effect.     

Using head-mounted displays to examine adaptation and calibration under varying perturbations

Simulator sickness has been a pervasive problem as head-mounted displays (HMDs) grow in popularity. Recent work showed that people can adapt to constant latency in an HMD, but latency that varies has not been examined. In this study, participants performed a shooting task while wearing an HMD during three sessions separated by 48 h under conditions of constant or varying latency. Performance was assessed for both accuracy (targets hit) and speed (time-to-hit targets). It was hypothesized that participants would adapt to constant, but not varying latency as indicated by decreasing simulator sickness over time. Further, it was hypothesized that participants would improve performance over time for both conditions due to practice, but the constant latency group would improve at a faster rate. Results showed reduced sickness with session regardless of latency condition. A similar trend was shown where performance improved with each session, with no effect of the latency condition. Change in sickness and performance were not correlated, suggesting that the changes were independently driven. These findings showed that people reduced sickness and improved performance with repeated exposure, even when experiencing different perturbations. This finding has implications for both HMDs and general understanding of the relationship between latency and adaptation.     

Effect of head-mounted displays on posture

OBJECTIVE: The aim of the present study was to determine if a wearable system based on a head-mounted display (HMD) causes users to alter their head position and adopt postures that place greater stress on the musculoskeletal system. BACKGROUND: HMDs are common output devices used with wearable computers. HMDs provide the wearer with visual information by projecting computer-generated virtual images in front of the eyes. Deviations of neck posture from a neutral upright position increase the stresses on the musculoskeletal system of the head and neck. METHOD: Seven paramedics simulated the treatment of a patient under a normal condition and when using an HMD wearable computer system. During the simulations a posture analysis was performed using the Rapid Upper Limb Assessment method. RESULTS: The postures adopted when wearing an HMD, as compared with a normal condition, scored significantly higher for the neck (z = 2.463, p < .05) and for overall body posture (left side of the body: z = 2.447, p < .05; right side of the body: z = 2.895, p < .05). CONCLUSION: Wearing an HMD can force the wearers to modify their neck posture. As such, the musculoskeletal system of the head and neck may be placed under increased levels of stress. APPLICATION: Potential users should be made aware that HMDs could dictate modifications in neck posture, which may have detrimental effects and may compound the weight effect of the HMD.     

Perceptual issues in the use of head-mounted visual displays

OBJECTIVE: We provide a review and analysis of much of the published literature on visual perception issues that impact the design and use of head-mounted displays (HMDs). BACKGROUND: Unlike the previous literature on HMDs, this review draws heavily from the basic vision literature in order to help provide insight for future design solutions for HMDs. METHOD: Included in this review are articles and books found cited in other works as well as articles and books obtained from an Internet search. RESULTS: Issues discussed include the effect of brightness and contrast on depth of field, dark focus, dark vergence, and perceptual constancy; the effect of accommodation-vergence synergy on perceptual constancy, eyestrain, and discomfort; the relationship of field of view to the functioning of different visual pathways and the types of visual-motor tasks mediated by them; the relationship of binocular input to visual suppression; and the importance of head movements, head tracking, and display update lag. CONCLUSION: This paper offers a set of recommendations for the design and use of HMDs. APPLICATION: Consideration of the basic vision literature will provide insight for future design solutions for HMDs.     

Sensitivity to visual speed modulation in head-mounted displays depends on fixation

A primary cause of simulator sickness in head-mounted displays (HMDs) is conflict between the visual scene displayed to the user and the visual scene expected by the brain when the user’s head is in motion. It is useful to measure perceptual sensitivity to visual speed modulation in HMDs because conditions that minimize this sensitivity may prove less likely to elicit simulator sickness. In prior research, we measured sensitivity to visual gain modulation during slow, passive, full-body yaw rotations and observed that sensitivity was reduced when subjects fixated a head-fixed target compared with when they fixated a scene-fixed target. In the current study, we investigated whether this pattern of results persists when (1) movements are faster, active head turns, and (2) visual stimuli are presented on an HMD rather than on a monitor. Subjects wore an Oculus Rift CV1 HMD and viewed a 3D scene of white points on a black background. On each trial, subjects moved their head from a central position to face a 15° eccentric target. During the head movement they fixated a point that was either head-fixed or scene-fixed, depending on condition. They then reported if the visual scene motion was too fast or too slow. Visual speed on subsequent trials was modulated according to a staircase procedure to find the speed increment that was just noticeable. Sensitivity to speed modulation during active head movement was reduced during head-fixed fixation, similar to what we observed during passive whole-body rotation. We conclude that fixation of a head-fixed target is an effective way to reduce sensitivity to visual speed modulation in HMDs, and may also be an effective strategy to reduce susceptibility to simulator sickness.     

Motion sickness, console video games, and head-mounted displays

OBJECTIVE: We evaluated the nauseogenic properties of commercial console video games (i.e., games that are sold to the public) when presented through a head-mounted display. BACKGROUND: Anecdotal reports suggest that motion sickness may occur among players of contemporary commercial console video games. METHODS: Participants played standard console video games using an Xbox game system. We varied the participants' posture (standing vs. sitting) and the game (two Xbox games). Participants played for up to 50 min and were asked to discontinue if they experienced any symptoms of motion sickness. RESULTS: Sickness occurred in all conditions, but it was more common during standing. During seated play there were significant differences in head motion between sick and well participants before the onset of motion sickness. CONCLUSION: The results indicate that commercial console video game systems can induce motion sickness when presented via a head-mounted display and support the hypothesis that motion sickness is preceded by instability in the control of seated posture. APPLICATION: Potential applications of this research include changes in the design of console video games and recommendations for how such systems should be used.     

Depth of focus and visual recognition of imagery presented on simultaneously viewed displays: implications for head-mounted displays

OBJECTIVE: We sought to determine the optimal focal distance for a semitransparent monocular head-mounted display (HMD) integrated with a flight simulator display and to investigate whether observers experienced visual discomfort or impaired target recognition when using an HMD set at the optimal distance. BACKGROUND: When an observer wears a monocular HMD and views a simulator display, focal distances of both displays must be within the observers' depth of focus to prevent blurred imagery. Because focal distance can vary by as much as 0.5 m in U.S. Air Force multifaceted simulator displays, we determined whether a monocular HMD could be integrated with a simulator display without blurred imagery or discomfort. METHOD: Depth of focus and visual recognition were measured with a staircase procedure, and visual discomfort was measured with a questionnaire. RESULTS: Depth of focus was 0.64 diopters in one condition tested, but it was affected by luminance level and display resolution. It was recommended that HMD focal distance equal the optical midpoint of the range of viewing distances encountered in the simulator. Moreover, wearing an HMD produced a decline in recognition performance for targets presented on the simulator display despite both displays being within observers' depth of focus and producing no visual discomfort. CONCLUSION: Monocular HMDs can be integrated with multifaceted simulator displays without blurred imagery or visual discomfort, provided that the correct focal distance is adopted. APPLICATION: For situations involving simultaneously viewed visual displays.     

Gaze point estimation on curved display by using session level calibration for flat screen displays

Multimedia Tools and Applications - The advantages of curved screen displays find their place in populations everyday life, therefore it is important to adapt the existing eye tracking systems for...     

眼球光心标定与距离修正的3维注视点估计

目的 在基于双目视线相交方法进行3维注视点估计的过程中,眼球光心3维坐标手工测量存在较大误差,且3维注视点估计结果在深度距离方向偏差较大。为此,提出了眼球光心标定与距离修正的方案对3维注视点估计模型进行改进。方法 首先,通过图像处理算法获取左右眼的PCCR（pupil center cornea reflection）矢量信息,并使用二阶多项式映射函数得到左、右眼的2维平面注视点;其次,通过眼球光心标定方法获取眼球光心的3维坐标,避免手工测量方法引入的误差;然后,结合平面注视点得到左、右眼的视线方向,计算视线交点得到初步的3维注视点;最后,针对结果在深度距离方向抖动较大的问题,使用深度方向数据滤波与Z平面截取修正法对3维注视点结果进行修正处理。结果 选择两个不同大小的空间测试,实验结果表明该方法在3050 cm的工作距离内,角度偏差0.7°,距离偏差17.8 mm,在50130 cm的工作距离内,角度偏差1.0°,距离偏差117.4 mm。与其他的3维注视点估计方法相比较,在同样的测试空间条件下,角度偏差和距离偏差均显著减小。结论 提出的眼球光心标定方法可以方便准确地获取眼球光心的3维坐标,避免手工测量方法带来的误差,对角度偏差的减小效果显著。提出的深度方向数据滤波与Z平面截取修正法可以有效抑制数据结果的抖动,对距离偏差的减小效果显著。     

Radiometric surface temperature calibration effects on satellite based evapotranspiration estimation

Agriculture on the Texas High Plains (THP) uses approximately 89% of groundwater withdrawals from the Ogallala Aquifer, leading to steady decline in water table levels. Therefore, efficient water management is essential for sustaining agricultural production in the THP. Accurate evapotranspiration (ET) maps provide critical information on actual spatio‐temporal crop water use. METRIC (Mapping Evapotranspiration at High Resolution using Internalized Calibration) is a remote sensing based energy balance method that uses radiometric surface temperature (T _s) for mapping ET. However, T _s calibration effects on satellite based ET estimation are less known. Further, METRIC has never been applied for the advective conditions of the semi‐arid THP. In this study, METRIC was applied and predicted ET was compared with measured values from five monolithic weighing lysimeters at the USDA‐ARS Conservation and Production Research Laboratory in Bushland, Texas, USA. Three different levels of calibration were applied on a Landsat 5 Thematic Mapper's thermal image acquired on 23 July 2006 to derive T _s. Application of METRIC on a MODTRAN calibrated image improved the accuracy of distributed ET prediction. In addition, ET estimates were further improved when a THP‐specific model was used for estimating leaf area index. Results indicated that METRIC performed well with ET mean bias error±root mean square error of 0.4±0.7 mm d^?1.     

Usability of the size,spacing, and operation method of virtual buttons with virtual hand on head-mounted displays

Virtual reality (VR) allows users to see and manipulate virtual scenes and items through input devices, like head-mounted displays. In this study, the effects of button size, spacing, and operation method on the usability of virtual buttons in VR environments were investigated. Task completion time, number of errors, and subjective preferences were collected to test different levels of the button size, spacing, and operation method. The experiment was conducted in a desktop setting with Oculus Rift and Leap motion. A total of 18 subjects performed a button selection task. The optimal levels of button size and spacing within the experimental conditions are 25 mm and between 5 mm and 9 mm, respectively. Button sizes of 15 mm with 1-mm spacing were too small to be used in VR environments. A trend of decreasing task completion time and the number of errors was observed as button size and spacing increased. However, large size and spacing may cause fatigue, due to continuous extension of the arms. For operation method, the touch method took a shorter task completion time. However, the push method recorded a smaller number of errors, owing to the visual push-feedback. In this paper, we discuss advantages and disadvantages in detail. The results can be applied to many different application areas with VR HMD using virtual hand interaction.     

Asynchronous distributed calibration for scalable and reconfigurable multi-projector displays

Centralized techniques have been used until now when automatically calibrating (both geometrically and photometrically) large high-resolution displays created by tiling multiple projectors in a 2D array. A centralized server managed all the projectors and also the camera(s) used to calibrate the display. In this paper, we propose an asynchronous distributed calibration methodology via a display unit called the plug-and-play projector (PPP). The PPP consists of a projector, camera, computation and communication unit, thus creating a self-sufficient module that enables an asynchronous distributed architecture for multi-projector displays. We present a single-program-multiple-data (SPMD) calibration algorithm that runs on each PPP and achieves a truly scalable and reconfigurable display without any input from the user. It instruments novel capabilities like adding/removing PPPs from the display dynamically, detecting faults, and reshaping the display to a reasonable rectangular shape to react to the addition/removal/faults. To the best of our knowledge, this is the first attempt to realize a completely asynchronous and distributed calibration architecture and methodology for multi-projector displays.     

针对多投影仪显示墙画面校正的图像对准技术

针对多投影仪显示墙画面校正问题中相机与投影仪间图像对准问题,提出一种基于自适应细分网格的稀疏对应点加密方法,可以得到任意光滑屏幕上投影图像与相机图像间的像素级对应关系。该方法利用改进的自适应4点插值细分曲线思想构造细分网格方法,可以将投影仪图像与相机图像间稀疏对应点网格加密到任意精度,从而建立从相机到投影仪图像间的像素级一一映射关系,为多投影仪显示墙系统的几何和色彩校正提供精确的图像对准基础。与现有算法的对比分析和虚拟机场塔台仿真系统中的实际应用表明,该方法具有较高的图像对准精度,并且无显式的需求投影仪、投影屏幕和相机的内部参数。     

Preferred viewing distance and screen angle of electronic paper displays

This study explored the viewing distance and screen angle for electronic paper (E-Paper) displays under various light sources, ambient illuminations, and character sizes. Data analysis showed that the mean viewing distance and screen angle were 495 mm and 123.7 degrees. The mean viewing distances for Kolin Chlorestic Liquid Crystal display was 500 mm, significantly longer than Sony electronic ink display, 491 mm. Screen angle for Kolin was 127.4 degrees, significantly greater than that of Sony, 120.0 degrees. Various light sources revealed no significant effect on viewing distances; nevertheless, they showed significant effect on screen angles. The screen angle for sunlight lamp (D65) was similar to that of fluorescent lamp (TL84), but greater than that of tungsten lamp (F). Ambient illumination and E-paper type had significant effects on viewing distance and screen angle. The higher the ambient illumination was, the longer the viewing distance and the lesser the screen angle. Character size had significant effect on viewing distances: the larger the character size, the longer the viewing distance. The results of this study indicated that the viewing distance for E-Paper was similar to that of visual display terminal (VDT) at around 500 mm, but greater than normal paper at about 360 mm. The mean screen angle was around 123.7 degrees, which in terms of viewing angle is 29.5 degrees below horizontal eye level. This result is similar to the general suggested viewing angle between 20 degrees and 50 degrees below the horizontal line of sight.     

Geometric estimation of nonlinear process systems

An estimation approach to jointly design the estimation model, data assimilation structure, and algorithm in the light of particular estimation objectives is developed within a constructive framework. On the basis of the detectability property which underlies the Lie derivative-based geometric estimator (GE) in conjunction with singular perturbation and robust stability tools, the GE is redesigned to remove its Lie derivation applicability obstacle. Then, the equivalence between the GE and the extended Kalman filter (EKF) is established, and the GE is endowed with uncertainty assessment capability. The resulting GE has: (i) a simple construction in terms of model Jacobians, (ii) a nonlocal convergence criterion coupled with easy to apply tuning guidelines, and (iii) the model and its detectability structure as key design degrees of freedom. The proposed methodology is illustrated and tested with an experimental binary distillation column.     

Noise estimation and reduction on five medical liquid‐crystal displays

Abstract— Liquid‐crystal displays (LCDs) are replacing cathode‐ray tube (CRT) displays as primary diagnostic viewing devices in clinics. They exhibit higher spatial noise than CRTs, which can interfere with diagnosis and reduce the efficiency especially when subtle abnormalities are presented. A study by the authors on LCD spatial noise has recently been reported. A high‐quality CCD camera was used to acquire images from the LCD. Noise properties were estimated from the digital‐camera images. Then, an error‐diffusion‐based operation was applied to reduce the display spatial noise. This paper presents the noise estimation and reduction results on five different medical‐grade LCDs using the same study protocol. These five different LCDs vary in terms of matrix size, pixel size, pixel structure, and vendors. The purpose of this work is to demonstrate that the LCD spatial‐noise estimation and reduction scheme proposed earlier by the authors is valid, robust, and necessary for various medicalgrade LCDs used in clinics today.     

Geometric and elastostatic calibration of robotic manipulator using partial pose measurements

The paper deals with the geometric and elastostatic calibration of robotic manipulator using partial pose measurements, which do not provide the end-effector orientation. The main attention is paid to the efficiency improvement of identification procedure. In contrast to previous works, the developed calibration technique is based on the direct measurements only. To improve the identification accuracy, it is proposed to use several reference points for each manipulator configuration. This allows avoiding the problem of non-homogeneity of the least-square objective, which arises in the classical identification technique with the full pose information (position and orientation). Its efficiency is confirmed by the comparison analysis, which deals with the accuracy evaluation of different identification strategies. The obtained theoretical results have been successfully applied to the geometric and elastostatic calibration of a serial industrial robot employed in a machining work cell for aerospace industry.