Differences between oculomotor and perceptual artifacts for temporally limited head mounted displays

We used perceptual and oculomotor measures to understand the negative impacts of low (phantom array) and high (motion blur) duty cycles with a high‐speed, AR‐likehead‐mounted display prototype. We observed large intersubject variability for the detection of phantom array artifacts but a highly consistent and systematic effect on saccadic eye movement targeting during low duty cycle presentations. This adverse effect on saccade endpoints was also related to an increased error rate in a perceptual discrimination task, showing a direct effect of display duty cycle on the perceptual quality. For high duty cycles, the probability of detecting motion blur increased during head movements, and this effect was elevated at lower refresh rates. We did not find an impact of the temporal display characteristics on compensatory eye movements during head motion (e.g., VOR). Together, our results allow us to quantify the tradeoff of different negative spatiotemporal impacts of user movements and make subsequent recommendations for optimized temporal HMD parameters.     

TORSO: Development of a Telexistence Visual System Using a 6-d.o.f. Robot Head

In telexistence master–slave systems, it is important to transmit visual information from remote places to the operator. Conventional imaging devices in head-mounted displays (HMDs) can only express the three-axis rotation of the neck. However, humans can obtain broader visual fields and motion parallax information from the translational motion of their necks. We have proposed a system that can acquire natural and comfortable visual information, and can accurately track the head motion of a person. Our proposed device can express the head motion and the translation movements of the neck. We have developed a robot, called 'TORSO', and constructed a telexistence visual system with a display device, HMD. In this paper, by means of a broader field of view achieved by motion involving looking around, we demonstrate the advantage and novelty of our proposed system. In addition, we suggest the evolution of the TORSO–HMD system.     

Estimating text legibility of a mobile display on the basis of translational vibration caused by walking

Abstract— In this study, the effect of vibration on mobile‐phone text legibility caused by walking was examined. Legibility was measured as reading performance and subjective task load when reading from a mobile‐phone display while walking on a treadmill at 1.5 km/hour, 3 km/hour, and an individually defined speed (3.9 km/hour on average). Vibration was measured on the vertical, lateral, and fore‐and‐aft axes during walking. Vibration amplitude was calculated in five different frequency bands (1, 2, 4, 8, and 16 Hz), and correlated with the legibility measures. The amplitude increased most on the vertical and fore‐and‐aft axes as a function of walking speed, and the increase was largest in the 2‐Hz frequency band. Legibility decreased concurrently with increasing vibration. The strong correlation between vibration characteristics and legibility measures suggests that vibration characteristics could, to some degree, be used in estimating small‐display legibility while walking.     

Review of: ‘ Programmed Instruction in the British Armed Forces’. By D. WALLIS,K. D. DUNCAN and M. A. G. KNIGHT. ( H.M.S.O., 1966.) [Pp. iv+49.] 4s. 6d.

A mathematical model for studying head protection in static is presented and its application to the design of ice hockey helmets is discussed. Static load and dynamic impact tests indicate that dynamic tests are to be preferred when estimating the stiffness of the materials used ns helmet liners. Solutions to the differential equations governing the linear motion of the head under a sideboard collision provide information regarding the thickness of the energy absorbing helmet liner and the tolerance level to which the helmet can be expected to perform. The model also provides a useful estimate of the angular velocity of the head imparted by the rebound from the sideboard. Although the helmet cannot prevent angular motion of the head, an estimate of the expected angular velocity may indicate that additional measures must be taken to prevent head injury from such angular motion. The study also indicates that the problem of providing head protection in ice hockey is of such magnitude that a helmet alone cannot be expected to provide total protection and additional modification to the playing environment must also be undertaken.     

Workstation variables and visual discomfort associated with VDTs

We have investigated the effects of a range of workstation factors upon the visual symptoms experienced by a group of 92 visual display terminal (VDT) users. Subjects in the study kept a diary over five consecutive working days in which they recorded the types of visual and postural symptoms which occurred and the types of work tasks being performed. Each subject's workstation was analysed for screen legibility and stability, discomfort and disability glare, and required head postures. By the use of multiple regression analysis techniques we have considered the relative contribution of these factors to the symptoms reported by the users of these workstations. Screen legibility significantly influenced the occurrence of symptoms of ocular discomfort and vertical head movements significantly affected the incidence of postural/headache symptoms.     

Design and evaluation of an augmented reality welding helmet

The article describes the development and ergonomic evaluation of an augmented reality (AR) welding helmet. The system provides an augmented user interface with supporting information relevant to the welding process. The experimental studies focused on hand–eye coordination of welders and nonwelders with two prototypes of the augmented reality welding helmet. The first prototype operated at 16 frames per second, whereas the second, improved version had 20 frames per second. In addition, the hand–eye coordination while wearing the welding helmet with video see‐through head‐mounted display was compared to a performance with natural vision, without any helmet. Experimental results showed significant influence of helmet and occupation on hand–eye coordination. Subjective assessment revealed better rating for stereo perception for the system with the higher frame rate, whereas no significant difference in performance was found between the two frame rates. © 2007 Wiley Periodicals, Inc. Hum Factors Man 17: 317–330, 2007.     

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.     

Conjugate‐optical retroreflector display system: Optical principles and perceptual issues

Abstract— Conjugate‐optical retroreflector (COR) display systems have the potential for providing inexpensive high‐resolution imagery in a head‐mounted display (HMD) configuration. There are several perceptual issues, however, that need to be addressed before a COR display system can be used effectively. One issue is the choice of projected‐image location relative to the retroreflective screen, which is determined by the convergence angle between the binocular channels of the COR display. Another issue involves visual half‐occlusions, which can occur when a portion of a stereoscopic image is visible to only one eye, as may occur in any HMD. If half occlusions are simulated in a COR display in a way that is inconsistent with natural viewing, undesirable perceptual effects may result. In the present paper, we first describe, the optical principles that underlie the COR display system. We then discuss the importance of binocular convergence and describe a COR display configuration that eliminates inconsistencies in the depth cues provided by displayed surface properties and halfocclusions.     

A multi‐plane optical see‐through head mounted display design for augmented reality applications

Augmented reality (AR) display technology greatly enhances users' perception of and interaction with the real world by superimposing a computer‐generated virtual scene on the real physical world. The main problem of the state‐of‐the‐art 3D AR head‐mounted displays (HMDs) is the accommodation‐vergence conflict because the 2D images displayed by flat panel devices are at a fixed distance from the eyes. In this paper, we present a design for an optical see‐through HMD utilizing multi‐plane display technology for AR applications. This approach manages to provide correct depth information and solves the accommodation‐vergence conflict problem. In our system, a projector projects slices of a 3D scene onto a stack of polymer‐stabilized liquid crystal scattering shutters in time sequence to reconstruct the 3D scene. The polymer‐stabilized liquid crystal shutters have sub‐millisecond switching time that enables sufficient number of shutters to achieve high depth resolution. A proof‐of‐concept two‐plane optical see‐through HMD prototype is demonstrated. Our design can be made lightweight, compact, with high resolution, and large depth range from near the eye to infinity and thus holds great potential for fatigue‐free AR HMDs.     

High luminance and high see‐through head‐mounted displays with beam‐splitter‐array waveguides

We have developed head‐mounted displays with high transmittance and luminance, which could be utilized outside safely without dimming glasses. We first specified required optical performance specifications by considering user's safety and usability. In order to ensure that the user is able to recognize both surrounding environment and the image of the head‐mounted display, we set the target specification that the transmittance is higher than or equal to 85%, and the luminance contrast ratio is larger than or equal to 1.15 with display image of white solid pattern. We then developed the beam‐splitter‐array waveguide to achieve the requirements. It has advantages in high efficiency and high see‐through property. In order to determine configuration of the waveguide, we have performed optical ray trace simulation. We also established versatile waveguide measurement method applicable to different‐type waveguides. By utilizing the waveguide we have developed, we made a prototype of a head‐mounted display (HMD) with high transmittance 94% and high luminance 4.8 × 10³ cd/m² and thus luminance contrast ratio 1.25 under the sun. With these advantages, our HMD is suitable for usage outside including applications of work support systems where dimming effect is not preferred, and the HMD is used under the sun.     

Effect of the field of view on perceiving world-referenced image motion during concurrent head movements

We have previously shown that concurrent head movements impair head-referenced image motion perception when compensatory eye movements are suppressed (Li, Adelstein, & Ellis, 2009) [16]. In this paper, we examined the effect of the field of view on perceiving world-referenced image motion during concurrent head movements. Participants rated the motion magnitude of a horizontally oscillating checkerboard image presented on a large screen while making yaw or pitch head movements, or holding their heads still. As the image motion was world-referenced, head motion elicited compensatory eye movements from the vestibular-ocular reflex to maintain the gaze on the display. The checkerboard image had either a large (73°H × 73°V) or a small (25°H × 25°V) field of view (FOV). We found that perceptual sensitivity to world-referenced image motion was reduced by 20% during yaw and pitch head movements compared to the veridical levels when the head was still, and this reduction did not depend on the display FOV size. Reducing the display FOV from 73°H × 73°V to 25°H × 25°V caused an overall underestimation of image motion by 7% across the head movement and head still conditions. We conclude that observers have reduced perceptual sensitivity to world-referenced image motion during concurrent head movements independent of the FOV size. The findings are applicable in the design of virtual environment countermeasures to mitigate perception of spurious motion arising from head tracking system latency.     

A systematic framework for on‐line calibration of a head‐mounted projection display for augmented‐reality systems

Abstract— Augmented reality (AR) is a technology in which computer‐generated virtual images are dynamically superimposed upon a real‐world scene to enhance a user's perceptions of the physical environment. A successful AR system requires that the overlaid digital information be aligned with the user's real‐world senses — a process known as registration. An accurate registration process requires the knowledge of both the intrinsic and extrinsic parameters of the viewing device and these parameters form the viewing and projection transformations for creating the simulations of virtual images. In our previous work, an easy off‐line calibration method in which an image‐based automatic matching method was used to establish the world‐to‐image correspondences was presented, and it is able to achieve subpixel accuracy. However, this off‐line method yields accurate registration only when a user's eye placements relative to the display device coincides with locations established during the offline calibration process. A likely deviation of eye placements, for instance, due to helmet slippage or user‐dependent factors such as interpupillary distance, will lead to misregistration. In this paper, a systematic on‐line calibration framework to refine the off‐line calibration results and to account for user‐dependent factors is presented. Specifically, based on an equivalent viewing projection model, a six‐parameter on‐line calibration method to refine the user‐dependent parameters in the viewing transformations is presented. Calibration procedures and results as well as evaluation experiments are described in detail. The evaluation experiments demonstrate the improvement of the registration accuracy.     

A psychophysical and questionnaire investigation on the spatial disorientation triggered by cockpit layout and design

This study assessed Taiwanese air force combat jet pilots' ability to cope with spatial disorientation (SD) triggered by cockpit layout and design. The measurement items of psychophysical questionnaire were ranked by 325 air force combat jet pilots. This study prioritized the causes of SD perceived by combat jet pilots resulted from the unfamiliarity with instruments on aircraft undergoing flight training, the aircraft's cockpit canopy and the layout of instruments in the cockpit. A significant difference was found between with-SD experience and without-SD experience subjects' responses from adapting to the size of instruments in the cockpit, and from the helmet-mounted display (HMD). Considerable association was discernible between the position of instruments in the cockpit and combat jet models accrued; as well as between the helmet-mounted display (HMD) and combat jet models accrued. The study identify main cockpit layout and design causing SD of Taiwanese pilots based on combat jet models to eliminate the risk of SD, intensify SD training on preventing SD and provide pilots with skills to anticipate and assess the risk of SD during mission planning, and provide references to the military for future procurement of new aircraft models.Relevance to industryThese results provide important information to the defense manufacturers for designing the cockpit layout of combat jets to prevent SD of specific pilots. Finally, the results show the contribution of ergonomics to support military operational commanders in the design of training and prevention of SD.     

Effects on visual functions during tasks of object handling in virtual environment with a head mounted display

This study examined the effects on visual functions of a prolonged handling task within the helmet-mounted display environment. Both version eye movement and accommodative response became gradually slower during the 40-min task. Although delayed presentation of display after head movement noticeably worsened both visual responses, presentation delay after hand movement did not significantly change the sluggishness of responses. Therefore it is suggested that decreasing time delay after head movement is a more important factor in order to improve human performance of handling tasks within the HMD environment.     

The impact of non‐immersive head‐mounted displays (HMDs) on the visual field

Abstract— Binocular head‐mounted displays (HMDs) that could be used non‐immersively produced substantial interruption of the visual field. Monocular HMDs designed to be used non‐immersively created minimal interruption of the visual fields. The scotomata are small enough to allow the HMD to be worn in mobile situations, but inattention associated with use of the HMD may cause safety concerns for some mobile situations. A small opaque display can be positioned to provide a see‐through functionality.     

Division model‐based distortion correction method for head‐mounted displays

In this paper, we present a simple and efficient method for correcting the asymmetric and nonlinear geometrical distortion of a head‐mounted display (HMD). The method divides the object space into a number of quadratic triangular elements and applies a quadratic predistortion for each image section so that it can handle the distortion with any complex shapes caused by the decentering and tilted optics and improve the calibration accuracy. The errors introduced in the process of fabricating and assembling can also be eliminated. We investigated the use of a quadratic division model and two types of linear division models on an off‐axis HMD to correct the optical distortion. Experimental results demonstrated that the quadratic division model converged at a faster rate and produced higher accuracy over the typical linear model. The average root of mean square error (RMSE) after distortion correction was one pixel, and the maximum standard deviations in all rows and columns were 0.67 pixel and 0.57 pixel. In addition, the deformation continuity is maintained by using the quadratic element with connected midside nodes.     

Feedback control for rotational movements in feature space

Synthesizing controllers for rotational movements in feature space is an open research problem and is particularly challenging because of the need to precisely regulate the character's global orientation, angular momentum and inertia. This paper presents feature‐based controllers for a wide variety of rotational movements, including cartwheels, dives and flips. We show that the controllers can be made robust to large external disturbances by using a time‐invariant control scheme. The generality of the control laws is demonstrated by providing examples of the flip controller with different apexes, the diving controller with different heights and styles, the cartwheel controller with different speeds and straddle widths, etc. The controllers do not rely on any input motion or offline optimization.     

Dynamics of a rotating flexible and symmetric spacecraft using impedance matrix in terms of the flexible appendages cantilever modes

The subject of this work is the dynamics of a rotating spacecraft. The spacecraft is modeled as a main rigid body connected to two flexible solar panels. The orbital motion of the whole spacecraft with a constant angular velocity is considered, interacting with small rigid motions of the main body, and small elastic deformations and infinitesimal vibrations of the solar panels. A continuum approach based on the Rayleigh–Ritz discretization is used to describe the distributed flexibility in the spacecraft. Rayleigh–Ritz discretization functions used are the clamped modes of the solar panels. This method enables us to construct the impedance matrix of the whole system relating to the displacement of the main body and the external torque. A spectral expansion of this impedance matrix, in terms of these clamped modes is obtained in the frequency domain. The numerical results presented show that for small values of orbital angular velocity, the vibration motion frequencies of the flexible parts (solar panels) are not perturbed substantially. Moreover, when great values of orbital angular velocity are simulated, these frequencies change considerably. The present investigation based on the Rayleigh–Ritz discretization shows the effect of the interaction between the orbital motion of the whole spacecraft and the vibration motions of the flexible parts.     

Subjective and objective evaluation of visual fatigue caused by continuous and discontinuous use of HMDs

During continuous use of displays, a short rest can relax users' eyes and relieve visual fatigue. As one of the most important devices of virtual reality, head‐mounted displays (HMDs) can create an immersive 3D virtual world. When users have a short rest during the using of HMDs, they will experience a transition from virtual world to real world. In order to investigate how this change affects users' eye condition, we designed a 2 × 2 experiment to explore the effects of short rest during continuous using of HMDs and compared the results with those of 2D displays. The Visual Fatigue Scale, critical flicker frequency, visual acuity, pupillary diameter, and accommodation response of 80 participants were measured to assess the subject's performance. The experimental results indicated that a short rest during the using of 2D displays could significantly reduce users' visual fatigue. However, the experimental results of using HMDs showed that short rest during continuous using of HMD induced more severe symptoms of subjectively visual discomfort, but reduced the objectively visual fatigue.     

Projection‐based head‐tracking 3‐D displays

Abstract— This paper describes the construction and operation of four 3‐D displays in which each display produces two images for each eye and thus fits into the category of projection‐based binocular stereoscopic displays. The four 3‐D displays described are pico‐projector‐based, liquid‐ crystal—on—silicon (LCOS) conventional projector‐based, 120‐Hz digital‐light‐processor (DLP) projector‐ based, and the HELIUM3D system. In the first three displays, images are produced on a direct‐view LCD whose conventional backlight is replaced with a projection illumination source that is controlled by a multi‐user head tracker; novel steering optics direct the projector output to regions referred to as exit pupils located at the viewers' eyes. In the HELIUM3D display, the image information is supplied by a horizontally scanned, fast, light valve whose output is controlled by a spatial light modulator (SLM) to direct images to the appropriate viewers' eyes. The current statu s and the multimodal potential of the HELIUM3D display are described.