Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and - 16° downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.     

The effects of visual display distance on eye accommodation, head posture, and vision and neck symptoms

OBJECTIVE: Determine the effects of display viewing distance on both the visual and musculoskeletal systems while the text height is held constant across viewing distances. BACKGROUND: The distance from the eyes to a computer display may affect visual and neck comfort. If the angular size of the characters remains the same, it is recommended that the display be placed at a farther viewing distance (e.g., 70-100 cm). However, in common usage, the character sizes are not adjusted based on viewing distance. METHOD: Participants under the age of 35 years (N = 24) performed visually demanding tasks using a computer display for 2 hr each at three viewing distances (mean: 52.4, 73.0, and 85.3 cm) while torso and head posture were tracked. At the end of each task, eye accommodation was measured and symptoms were recorded. RESULTS: The near distance was associated with significantly less blurred vision, less dry or irritated eyes, less headache, and improved convergence recovery when compared with the middle and far distances. Participants moved their torsos and heads closer to the monitor at the far distance. CONCLUSION: If the computer screen character sizes are close to the limits of visual acuity, it is recommended that the computer monitor be positioned between the near (52 cm) and middle (73 cm) distance from the eyes. APPLICATION: The location of a computer display should take into account the size of the characters on the screen and the visual acuity of the user.     

True 3‐D scanned voxel displays using single or multiple light sources

Abstract— Conventional stereoscopic displays require viewers to unnaturally keep eye accommodation fixed at one focal distance while they dynamically change vergence to view objects at different distances. This forced decoupling of reflexively linked processes fatigues eyes, causes discomfort, compromises image quality, and may lead to pathologies in developing visual systems. Volumetric displays can overcome this conflict, but only for small objects placed within a limited range of viewing distances and accommodation levels, and cannot render occlusion cues correctly. Our multi‐planar True 3‐D displays generate accommodation cues that match vergence and stereoscopic retinal disparity demands and can display images and objects at viewing distances throughout the full range of human accommodation (from 6.25 cm to infinity), better mimicking natural vision and minimizing eye fatigue.     

Limits of fusion and depth judgment in stereoscopic color displays

The effective use of stereoscopic display systems is dependent, in part, on reliable data describing binocular fusion limits and the accuracy of depth discrimination for such visual display devices. These issues were addressed in three experiments, as were the effects of interocular cross talk. Results showed that limits of fusion were approximately 27.0 min arc for crossed disparity and 24.0 min arc for uncrossed disparity. Subjects were extremely accurate in distinguishing the relative distance among four groups of stimuli, were able to identify a pair of stimuli colocated at the same depth plane within each group, and were fairly accurate in scaling stimuli along the depth dimension. The mean error in using disparity as a depth cue was approximately 2.2 min arc. Interocular cross talk had little effect on fusion limits for 200-ms stimulus presentations but significantly affected fusion for longer (2 s) presentations that enabled vergence responses to be executed. Depth discrimination performance was essentially unaffected by interocular cross talk; however, cross talk significantly influenced subjective ratings of image quality and visual comfort.     

Industrial inspection performance depends on both viewing distance and oculomotor characteristics.

The influence of viewing distance and individual differences in the oculomotor resting states (dark vergence and dark focus) on both inspection performance and visual fatigue was investigated by asking 24 college students to perform a visual inspection task for 40 min twice, once with a 20 cm viewing distance and once with a 60 cm viewing distance. During the task participants visually searched enlarged images of contact lenses for six different types of defects. Lens images were presented at a constant visual angle (17.5 degrees) on a CRT. Inspection performance varied significantly across the two viewing distances: participants spent on average more than twice as much time inspecting individual lenses in the near condition (mean = 18.32 s lens(-1)) than in the far condition (mean = 7.25 s lens(-1)). Participants also reported greater visual fatigue in the near condition than in the far condition. At both viewing distances, participants who experienced relatively large inward shifts in dark vergence also tended to be slow inspectors. Neither inspection performance nor measures of fatigue were related to dark focus. These results support existing evidence against the use of near viewing distances and suggest that an oculomotor mechanism links inspection performance and visual fatigue to viewing distance.     

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.     

Eye movements and visual discomfort when viewing stereoscopic 3D content

The visual brain fuses the left and right images projected onto the two eyes from a stereoscopic 3D (S3D) display, perceives parallax, and rebuilds a sense of depth. In this process, the eyes adjust vergence and accommodation to adapt to the depths and parallax of the points they gazed at. Conflicts between accommodation and vergence when viewing S3D content potentially lead to visual discomfort. A variety of approaches have been taken towards understanding the perceptual bases of discomfort felt when viewing S3D, including extreme disparities or disparity gradients, negative disparities, dichoptic presentations, and so on. However less effort has been applied towards understanding the role of eye movements as they relate to visual discomfort when viewing S3D. To study eye movements in the context of S3D viewing discomfort, a Shifted-S3D-Image-Database (SSID) is constructed using 11 original nature scene S3D images and their 6 shifted versions. We conducted eye-tracking experiments on humans viewing S3D images in SSID while simultaneously collecting their judgments of experienced visual discomfort. From the collected eye-tracking data, regions of interest (ROIs) were extracted by kernel density estimation using the fixation data, and an empirical formula fitted between the disparities of salient objects marked by the ROIs and the mean opinion scores (MOS). Finally, eye-tracking data was used to analyze the eye movement characteristics related to S3D image quality. Fifteen eye movement features were extracted, and a visual discomfort predication model learned using a support vector regressor (SVR). By analyzing the correlations between features and MOS, we conclude that angular disparity features have a strong correlation with human judgments of discomfort.     

Super multi‐view 3D displays reduce conflict between accommodative and vergence responses

A conflict between accommodation and vergence is one possible cause of visual fatigue and discomfort while viewing conventional three‐dimensional displays. Previous studies have proposed the super multi‐view (SMV) display technique to solve the vergence–accommodation conflict, in which two or more parallax images enter the pupil of the eye with highly directional rays. We simultaneously measured accommodative, vergence, and pupillary responses to SMV three‐dimensional displays to examine whether they can reduce the conflict. For comparison, responses to two‐view stereo images and real objects were also measured. The results show that the range of the accommodative response was increased by the SMV images compared with the two‐view images. The slope of the accommodation–vergence response function for the SMV images was similar to that for the real objects rather than the two‐view images. We also found that enhancement of the accommodative range by the SMV images is noticeable with binocular viewing, indicating that vergence‐induced accommodation plays an important role in viewing SMV displays. These results suggest that SMV displays induced a more natural accommodative response than did conventional, two‐view stereo displays. As a result, SMV displays reduced the vergence–accommodation conflict.     

Eyestrain in VDU users: viewing distance and the resting position of ocular muscles

Without fixation stimuli--for instance, in darkness--accommodation and convergence of the eyes reach an intermediate state that is relatively stable within a subject but which ranges from about 30 cm to infinity across subjects. This study investigated whether these oculomotor positions in darkness are related to visual strain. During work at a visual display unit (VDU), visual strain at a viewing distance of 50 cm was stronger than at 100 cm (with characters twice as large). The more distant the individual's dark convergence, the greater was the visual strain at the 50-cm viewing distance. When subjects were free to adjust the viewing distance to their comfort level, they chose distances between 51 and 99 cm (mean 74 cm) with characters 5 mm tall.     

Using electromyography responses to investigate the effects of the display type,viewing distance,and viewing time on visual fatigue

The rapid success of 3D display technology and daily accessibility to 3D images has greatly increased the interest in such applications for a wide range of fields. This paper compares the effects of watching movies with 2D and 3D displays depending on the viewing distance (3H vs. 6H, where H is the height of the screen) and viewing time to determine the visual fatigue using electromyography (EMG) in terms of the percentage of maximum voluntary contraction (%MVC) of the orbicularis oculi (OO) muscle activity and a subjective visual discomfort score. Twenty healthy male university students with a mean age of 27.7 ± 2.53 years participated in this study as volunteers. None had color blindness, and all had normal vision acuity. A mixed-measures design was performed. The results showed that the viewing time and distance had significant effects on the %MVC and OO muscle activity depending on the display type. Watching the 3D display from a short viewing distance produced significantly high visual fatigue compared to watching the 2D display from a short viewing distance. However, the 3D display seemed to be less stressful than the 2D display at long viewing distances.     

Visual discrimination on colour VDTs at two viewing distances

The paper describes a research study on visual discrimination of textual and graphic symbols on a visual display terminal (VDT) screen when viewed at eye-lo-screen distances of 61 cm and 152 cm (24 and 60 ins). Conducted as part of a development programme at McDonnell Douglas Corporation's St. Louis Aircraft Company for an Integrated Manufacturing Composites Centre (ICC), the study investigated symbol shapes, symbol sizes, symbol colours and background colours at the two viewing distances. The longer distance is representative of required placements of the VDTs at some manufacturing workstations to avoid interference with process or control equipment. Knowledge gained from the study was incorporated in the selection of the manufacturing computer information system (CIS) terminals.

All four treatments showed significant effects on visual discrimination at both viewing distances and, particularly at the 152 cm distance, the mix of symbol and background colours was highly significant. A black screen background colour with more luminous symbols such as orange, green, yellow provided much better visual discrimination at the extended viewing distance than less luminous symbols such as red and blue on a white background. Visual discrimination at the extended viewing distance, when compared with the shorter viewing distance and using symbols of equal size, was better than the loss in visual angle would suggest.

Sex and age (to age 65) did not significantly affect visual discrimination mean scores, but the variance among individuals in the 51-65 years age group was greater than for the younger age groups.

The visual discrimination scores for symbol sizes of 4 mm² were not significantly different from the 6 mm² symbols at the 61 cm viewing distance. The 4 mm² symbol size was therefore adequate for visual discrimination of standalone symbols at this distance. Although 8 mm symbols were not used in this study, projections from the data indicate that such symbol sizes at 152 cm would provide comparable discrimination scores to the 4 mm² at 61 cm.

Improved visual discrimination of standalone symbols occurs with gaps or changes in the angles of symbols, such as sets 'C' versus 'O' and 'Xl' versus'+'.     

The relation of vergence effort to reports of visual fatigue following prolonged near work

Two experiments examined the link between vergence effort and subjective reports of visual fatigue following prolonged near work. In Experiment 1, dark vergence and reports of visual fatigue symptoms associated with computer use were measured in 104 persons. Dark vergence was significantly correlated with four of six symptoms of visual fatigue. In Experiment 2, 16 subjects who exhibited clear "Heuer effects" (systematic gaze-related changes in dark vergence) read from a video display terminal (VDT) at a distance of 20 cm for 60 min under two gaze elevation conditions: 20 deg above and 20 deg below a baseline gaze elevation. This manipulation was designed to vary the amount of vergence effort required to fixate the VDT. Results indicate a positive relation between vergence effort and visual fatigue both within and between subjects, and that prolonged near work leads to decreased vergence accuracy at far distances. Implications for VDT workstation design are discussed.     

Visual display height

We examined the influence of backrest inclination and vergence demand on the posture and gaze angle that workers adopt to view visual targets placed in different vertical locations. In the study, 12 participants viewed a small video monitor placed in 7 locations around a 0.65-m radius arc (from 65 degrees below to 30 degrees above horizontal eye height). Trunk posture was manipulated by changing the backrest inclination of an adjustable chair. Vergence demand was manipulated by using ophthalmic lenses and prisms to mimic the visual consequences of varying target distance. Changes in vertical target location caused large changes in atlanto-occipital posture and gaze angle. Cervical posture was altered to a lesser extent by changes in vertical target location. Participants compensated for changes in backrest inclination by changing cervical posture, though they did not significantly alter atlanto-occipital posture and gaze angle. The posture adopted to view any target represents a compromise between visual and musculoskeletal demands. These results provide support for the argument that the optimal location of visual targets is at least 15 degrees below horizontal eye level. Actual or potential applications of this work include the layout of computer workstations and the viewing of displays from a seated posture.     

Impact of depth of field simulation on visual fatigue: Who are impacted? and how?

While stereoscopic content can be compelling, it is not always comfortable for users to interact with on a regular basis. This is because the stereoscopic content on displays viewed at a short distance has been associated with different symptoms such as eye-strain, visual discomfort, and even nausea. Many of these symptoms have been attributed to cue conflict, for example between vergence and accommodation. To resolve those conflicts, volumetric and other displays have been proposed to improve the user's experience. However, these displays are expensive, unduly restrict viewing position, or provide poor image quality. As a result, commercial solutions are not readily available. We hypothesized that some of the discomfort and fatigue symptoms exhibited from viewing in stereoscopic displays may result from a mismatch between stereopsis and blur, rather than between sensed accommodation and vergence. To find factors that may support or disprove this claim, we built a real-time gaze-contingent system that simulates depth of field (DOF) that is associated with accommodation at the virtual depth of the point of regard (POR). Subsequently, a series of experiments evaluated the impact of DOF on people of different age groups (younger versus older adults). The difference between short duration discomfort and fatigue due to prolonged viewing was also examined. Results indicated that age may be a determining factor for a user's experience of DOF. There was also a major difference in a user's perception of viewing comfort during short-term exposure and prolonged viewing. Primarily, people did not find that the presence of DOF enhanced short-term viewing comfort, while DOF alleviated some symptoms of visual fatigue but not all.     

Measurement of minimum angle of resolution (MAR) in the stereoscopic display using the optotype of stereoscopic stimuli

In stereoscopic images, the crossing point of the viewing directions of the two eyes determines the perceived depth. Assuming that accommodation is affected by the positions of the crossing point, the effect of crossing point on minimum angle of resolution (MAR) was investigated. For 40 participants, MAR was measured by two‐alternative forced choice where Snellen optotype E of up and down directions were used as two kinds of stimuli. As the crossing point of the viewing direction of the left and right eyes moves farther from the sample display, the ability to identify the direction of letter E decreases at the optotype of the same line thickness. The change of MAR shows linear trends with respect to the optical power change that are the reciprocal of the distance from the participant to the crossing points located out of screen and on screen.     

Electronic paper display preferred viewing distance and character size for different age groups

This study explores the preferred viewing distance and character size for an electronic paper display for three age groups. Proofreading speed and accuracy ratio were measured during Chinese proofreading tests using the preferred character size and minimum acceptable character size. Data analysis showed that the mean preferred viewing distance for young, middle-aged and older groups was 503, 455 and 444 mm, respectively. The mean preferred character size determined by young, middle-aged and older groups was 42.0, 50.0 and 55.2 min arc, respectively. The proofreading test results indicated that the older group proofread significantly more slowly (1.25 word/sec) than the young (1.76 word/sec) and middle-aged groups (1.74 word/sec). Further, the participants proofread more correctly with their preferred character size (73.3%) than with their minimum acceptable character size (65.4%). This study provides valuable information for the design of Chinese text presentations for various age groups. STATEMENT OF RELEVANCE: This study confirmed the preferred viewing distance and character size for E-paper display were influenced by age. The preferred Chinese character size for young, middle-aged and older people was 42, 50 and 55 min arc, respectively. Therefore, the age factor should be considered for E-paper displays design and video display terminal (VDT) guidelines.     

Super multi-view and holographic displays using MEMS devices

Holographic displays and super multi-view (SMV) displays have been developed to solve the accommodation–vergence conflict that is responsible for visual fatigue caused by the 3D images that are generated by conventional three-dimensional (3D) displays upon which the eye cannot focus. However, holographic and SMV displays provide 3D images upon which the eye can readily focus so that the accommodation–vergence conflict does not occur. Because these two display techniques require the generation of a very large amount of image data, the high data bandwidth of microelectromechanical (MEMS) devices is effectively utilized. The present article describes the holographic display system that employs a MEMS spatial light modulator (SLM), which increases the screen size and viewing zone angle. Two SMV displays are also described, where one employs MEMS SLMs and the other an array of MEMS projectors. The resolution and the number of viewpoints of the SMV displays have increased. Moreover, the technique using a MEMS SLM to eliminate speckles from holographic reconstructed images is also described.     

基于人眼视觉原理的虚拟现实显示模型

针对虚拟现实领域现有的显示模块无法提供满足人眼视觉规律的立体视觉效果这一问题,提出一种基于斜交视锥体立体摄像机模型的虚拟现实(VR)立体视觉解决方案。首先,通过研究人眼视域模型和人眼双目提取深度信息原理,建立双目视差数学模型;其次,使用工业引擎3DVIA Studio作为实验平台,依靠VSL编程语言进行画面分屏处理,通过设立父子关系,设置视觉交互模块,搭建VR交互立体摄像机结构;接着,通过建立点云模型,量化物体立体感观,探讨多种VR立体摄像机模型,从深度信息显示效果和畸变特性出发分析各个模型优缺点,逐步进行优化。分别建立了中心轴平行的正交视锥体摄像机模型、中心轴于观影距离处相交的正交视锥体模型,通过优化摄像机视锥体结构,形成斜交视锥体摄像机模型。最后使用3DVIA Studio进行实验,代入具体数据进行投影变换,结果显示斜交视锥体摄像机模型在保证深度信息显示效果的前提下很好地消除了畸变,能够提供优秀的视觉体验效果。     

Preferred viewing distance of liquid crystal high-definition television

This study explored the effect of TV size, illumination, and viewing angle on preferred viewing distance in high-definition liquid crystal display televisions (HDTV). Results showed that the mean preferred viewing distance was 2856 mm. TV size and illumination significantly affected preferred viewing distance. The larger the screen size, the greater the preferred viewing distance, at around 3-4 times the width of the screen (W). The greater the illumination, the greater the preferred viewing distance. Viewing angle also correlated significantly with preferred viewing distance. The more deflected from direct frontal view, the shorter the preferred viewing distance seemed to be.     

Effects of illumination conditions on preferred viewing distance of portable liquid‐crystal television

This study explored the effect of TV size, light source, and ambient illumination on the preferred viewing distance of portable liquid‐crystal‐display televisions. Results showed that the mean preferred viewing distance was 1389 mm. TV size had significant effects on preferred viewing distance. The larger the screen size, the greater the preferred viewing distance, at around 6.7–14.7 times the width of the screen (W). Light sources revealed no significant effect on preferred viewing distance. The effect of ambient illumination on preferred viewing distance was significant. The higher the ambient illumination was, the longer the preferred viewing distance.