Visual accommodation and subject performance during a stereographic object task using liquid crystal shutters

Virtual reality has become popular in a variety of fields. Three experiments to study visual accommodation and task performance during stereographic vision were carried out in order to better understand the human response to virtual reality. Visual accommodation to stereograms on CRT was studied. Subjects could see the target on the CRT display binocularly through liquid crystal shutters. Accommodation to a stereogram with step changes in distance was tested first. As the second experiment, accommodation to a stereogram with gradual changes in distance, and comparison of ability to perform a colour photograph stereogram task were tested. Finally, accommodation and subject performance during a prolonged stereographic object task were observed for 30min. A virtual ‘gate’ was formed at a position 1.2?m from the subject. The virtual target moved forward and backward through this gate between the positions of 0.8?m and 20?m. The subjects were asked to focus on the target and press a button as it moved through the virtual gate. Subjective response to the task and the error between the position where the button was pressed and the gate was recorded. It was concluded that there are some people who exhibit large changes in accommodation while performing a stereographic task. There is a tendency to accommodate to a distance nearer than the baseline. Prolonged stereoscopic viewing caused visual fatigue or loss of accommodation and diminished task performance.     

The effect of VDU colour on visual fatigue in the fovea and periphery of the visual field

The effect of the display of a visual display unit (VDU) on visual fatigue was investigated using the critical flicker frequency (CFF) paradigm. The results indicate that fatigue, as measured by CFF, varied as the VDU colour and eccentricity changed in the visual field. It was found that blue and red, that is, both extremes of the visible spectrum, strongly caused visual fatigue in the visual field when compared to green and yellow, that is, the middle range of the visible spectrum. Furthermore, for yellow and blue, VDU signal fatigue tended to decrease as the distance from the fovea increased. whereas for red and green, it increased by up to 10° in the periphery and then tended to decrease. The results indicate that yellow and green cause less fatigue in the periphery and fovea, respectively.     

Colour names and focal colours on electronic displays

This study identified the colours that were perceived as being the best examples (focal colours) of 10 common colour names when viewed on an electronic display. A total of 204 colours derived from a reflective surface colour measurement system (Munsell) were converted to the Commission Internationale de l'Eclairage (CIE) 1976 system and presented on a cathode ray tube (CRT). Forty subjects chose what was perceived as the best examples for each of the following colour terms: purple, blue, aqua, green, yellow, orange, red, pink, grey, and white. Results show that focal colours on a CRT do not always correspond to the typical colours used or to the best examples for reflective surface colours. The display designer should consider these differences when selecting colours for a display.     

Accommodation,convergence, pupil diameter and eye blinks at a CRT display flickering near fusion limit

Abstract

This study investigates possible effects of temporally modulated light stimulation near critical fusion frequency (CFF) when subjects observe a cathode ray tube (CRT) operated at different refresh rates. Various visual functions were measured in a series of tests of 2.5 min duration. In experiment 1, at a repetition rate of 50 Hz mean pupil size was 0.055 mm smaller than at 300 Hz. The precision of convergence and accommodation in binocular vision was not affected. In experiment 2, 300 Hz was compared with the lowest frequency that did not produce visible flicker for each subject. At the lower rate (55 to 90Hz), mean accommodation in monocular vision was 006 D weaker, median eye blink duration was 6% shorter, and mean eye blink interval was 15% longer. Individual differences and possible fatigue effects of intermittent light at visual display units are discussed.     

Subjective reactions to misconvergence on a colour display

Subjective ratings of various degrees of misconvergence were obtained from subjects viewing text and graphics pictures on a 355 mm high-resolution shadow mask colour CRT display. The pictures were displayed in four secondary colours: white, yellow, turquoise (cyan), and pink (magenta). In commercial applications, user acceptance and satisfaction often present more stringent requirements for front-of-screen quality than do objective performance criteria such as legibility. In this case, it is expected that the picture quality would become unacceptable at lower levels of misconvergence than would cause it to be considered illegible. The results show a marked degradation in apparent quality of convergence as misconvergence increases from about 0.2 mm to about 0.5 mm. To obtain subjectively acceptable picture quality, misconvergence should be no more than about 0.3 mm and should be better than 0.2 mm over the majority of the screen. (The spot size of the display used was about 0.8 mm.) Textual and graphical pictures did not produce significantly different results.     

Effects of display technologies on operation performances and visual fatigue

The use of 3D stereoscopic display technology in all aspects of life has attracted considerable research attention. However, only few studies have simultaneously considered the effects of stereoscopic display technologies on visual fatigue and operating performances. This study with 36 participants (50% females; mean age = 23.17 years, SD = 3.3) analyzed the effects of display technologies, task complexity, and use time on operation performances, subjective and objective visual fatigue. Results indicated that display technology did not significantly affect the operation performances, whereas task complexity did. However, no interaction took place between them. Display technology had no significant effects on subjective visual fatigue and near-point accommodation (NPA) but affected critical fusion frequency (CFF) significantly. Use time had significant effects on both subjective and objective visual fatigue.     

Temporal variation in the luminance level of stimuli displayed on a cathode-ray tube monitor: effects on performance on a visual vigilance task

This paper assesses the extent to which the sensitivity decrement frequently observed in vigilance tasks is affected by temporal variations in the luminance level of the stimuli displayed on the screen of a cathode-ray tube (CRT) monitor. First, it was confirmed that the luminance of the stimuli displayed on the screen of the CRT monitor decreases substantially during the first hour after turning the monitor on, and then it remains quite stable. Second, an experiment was carried out in which participants performed a visual vigilance task at three different time periods within which the luminance of the stimuli displayed on the screen of a CRT monitor either decreased or remained stable. The results indicate that the vigilance decrement is modulated by temporal fluctuations of the luminance of the monitor screen, which is used to display the stimuli. However, the relationship between both variables is not simple: the largest sensitivity decrement was not associated with the largest luminance decrement, but to a medium luminance decrement.     

Temporal variation in the luminance level of stimuli displayed on a cathode-ray tube monitor: effects on performance on a visual vigilance task

This paper assesses the extent to which the sensitivity decrement frequently observed in vigilance tasks is affected by temporal variations in the luminance level of the stimuli displayed on the screen of a cathode-ray tube (CRT) monitor. First, it was confirmed that the luminance of the stimuli displayed on the screen of the CRT monitor decreases substantially during the first hour after turning the monitor on, and then it remains quite stable. Second, an experiment was carried out in which participants performed a visual vigilance task at three different time periods within which the luminance of the stimuli displayed on the screen of a CRT monitor either decreased or remained stable. The results indicate that the vigilance decrement is modulated by temporal fluctuations of the luminance of the monitor screen, which is used to display the stimuli. However, the relationship between both variables is not simple: the largest sensitivity decrement was not associated with the largest luminance decrement, but to a medium luminance decrement.     

Some consequences of the shadow-mask CRT dot structure

The major CRT technology contender for multi-colour displays is the shadow-mask tube in one of its several variants. In each variant the phosphor screen structure is finely divided into a regular pattern of red, green and blue emitting phosphors with the expectation that this pattern of individual emission will visually fuse together to produce a clean image of the desired resultant colour. This paper discusses some of the consequences of the screen structure. This includes an analysis of the visual effects of the screen structure, including colour errors, symbol degradation and raster interference, leading to recommendations on the pitch of the screen structure in relation to the electron beam spot size. Recommendations are given on how to define and measure CRT ‘brightness’ and ‘line width’ parameters in the presence of the screen structure.     

Visual accommodation changes in VDU-operators related to environmental lighting and screen quality

Abstract

Visual problems involved in the operation of display units have been investigated in several studies (Höller et al. 1975, Läubli et al. 1980). The results of these studies indicate mainly that visual tasks using VDU terminals may induce temporary effects in the visual accommodation system. There are, however, suggestions that visual impairment of the task depends, among other factors, particularly on workstation lighting and screen quality (Östberg 1978, Läubli et al. 1980).

In the present pilot study an attempt was made to investigate possible relations between (i) operators' accommodation changes after six hours work at a display unit and (ii) work-station lighting and screen characteristics. The measurements were carried out in two separate field studies at a Telecom Directory Enquiry Center. Operator's visual accommodation before and after work, workplace lighting, luminance contrasts and screen qualities of 29 display screen operators were measured during day and night shifts. Field laser optometry was used for determining the state of visual accommodation. Photometric and radiometric characteristics of the display screens were measured using an EG & G spectrometer-photometer.

The study revealed a low significant relationship between lighting conditions on the one side and incidence of accommodation changes on the other. More operators showed over-accommodation when working at workplaces with higher luminance contrast. The influence of screen characteristics, such as screen illuminance, luminance and irradiance upon visual accommodation were evident during the night shift.     

Effects of display format and colour coding schemes on visual monitoring performance using spatially and temporally distributed visual displays

The present study examined factors that decreased task complexity so that a technology which temporally, rather than spatially, distributed information (i.e. RAP COM, for rapid communication) would result in performace advantages. This was accomplished by physically integrating the stimulus information into either the display format (i.e. an analog format) or into the response coding scheme (i.e. a colour coding scheme). Performance using the RAP COM display indicated a lower proportion of errors for the analog than for the digital format; however, a longer mean response time for a correct response was found for the analog than for the digital format. Two colour coding response schemes were used: (a)_a continuous scheme that comparised gradual changes between red and blue; (b) a distinctive scheme consisting of the colours cyan, green, yellow, orange, red, mauve, purple and blue. When the continuous colour coding responses scheme was used, performance using the RAP COM display, as compared with the spatial display, was no different after extended practice. The results of these experiments taken together indicate that the RAP COM display type may be a viable technology for some limited ‘real world’ environments.     

大型全彩色LED显示屏系统的设计与实现

现今,全彩色L E D显示屏已经成为了平板显示器的一个重要产品。本文设计了一种大型点阵L E D显示屏系统,其显示屏的点阵数为320*256,能显示红、黄、绿三色的任意点阵数据。本系统的设计可以完成点阵数据的生成、提取、处理、传输以及对显示屏的实时控制。     

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m(-2) without city noise; (2) a calculating task on a VDT with luminance of 20 cd m(-2) without city noise; (3) a calculating task on a VDT with luminance of 90 cd m(-2) with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m(-2) with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the high-luminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.     

Surmised state of accommodation to stereoscopic three-dimensional images with binocular disparity

Three-dimensional image (3-D image) was experimentally generated by the binocular disparity principle, and psychological tests were performed in relation to the state of accommodation. An image of a square formed by the time-sharing system using liquid crystal (LC) shutter glasses was displayed before the CRT screen (forward image) by the crossed visual-line method and behind the monitor screen (backward image) by the non-crossed visual-line method. The subjects were requested to subjectively compare each image with the original image on the CRT screen in relation to the size. The forward image displayed by the crossed visual lines looked smaller than the original image, while the backward image displayed by the non-crossed visual lines looked larger. In consideration of the developmental mechanism of micropsia occurring in patients with accommodative palsy or paresis of accommodation and macropsia occurring in patients with accommodative spasm, it was surmised that, in the generation of 3-D image due to binocular disparity, accommodation works so that the original image position is maintained.     

Physiological effects of intermittently illuminated textual displays

Optical equipment was developed to simulate visual display terminals (VDTs) with reversed presentation (bright background and dark characters). The decay time and mean luminance were kept constant, while the oscillating frequency varied. During one experiment subjects had to read text aloud for 60min. Before and after the reading, near point distance, critical flicker fusion frequency (CFF), visual acuity, stereo depth perception, lateral heterophoria and contrast sensitivity were measured. The 30 subjects had then to report their subjective reactions on a questionnaire. The following frequencies were used: 0, 30, 60, 90, 180 Hz. In addition subjects read a normally printed text with a luminance of 75 or 150 cd/m². The main finding was that of a strong decrease of the CFF after exposure to 30 and 60 Hz. It is suggested that for reversed presentation the refresh rate should be higher than 90 Hz.     

No evidence for prolonged latency of saccadic eye movements due to intermittent light of a CRT computer screen

Despite previous studies it remains unclear, whether saccadic eye movements across computer screens may be adversely affected by the intermittency of light of cathode ray tubes (CRT). We measured the latency of simple saccades to peripheral targets presented on a CRT-screen, operated at refresh rates of 50, 100 and 150 Hz, compared with a special fluorescent lamp display (FLD). Our results suggest that the intermittent light of CRT screens does not prolong the latency of saccades not even relative to a control condition of unmodulated steady light at the FLD. Further, there was no evidence for any individual effect in possibly susceptible subjects, e.g. at high critical flicker frequencies (CFF).     

Effect of visual display terminal height on the trapezius muscle hardness: quantitative evaluation by a newly developed muscle hardness meter

The aim of this study was to determine trapezius muscle hardness in 9 healthy volunteers before and after word processing tasks with a video display terminal (VDT) at three different heights. When using a desktop personal computer (PC), no change was observed in muscle hardness even after a 30-min task if a subject was in the reference posture with a declination angle formed by the Reid's line directed toward the upper edge of the PC screen and the horizontal plane within 5-10 degrees. However, an increase in muscle hardness was observed after a 15-min task in a posture of looking up at the screen (angle of elevation: 15-20 degrees) and after a 30-min task in a posture of looking down at the screen (angle of declination: 15-20 degrees). When the same tasks were performed with a notebook PC, muscle hardness increased after 15 min. Fifteen minutes of relaxation exercise reduced the muscle hardness caused by VDT work.     

No evidence for prolonged latency of saccadic eye movements due to intermittent light of a CRT computer screen

Despite previous studies it remains unclear, whether saccadic eye movements across computer screens may be adversely affected by the intermittency of light of cathode ray tubes (CRT). We measured the latency of simple saccades to peripheral targets presented on a CRT-screen, operated at refresh rates of 50, 100 and 150 Hz, compared with a special fluorescent lamp display (FLD). Our results suggest that the intermittent light of CRT screens does not prolong the latency of saccades not even relative to a control condition of unmodulated steady light at the FLD. Further, there was no evidence for any individual effect in possibly susceptible subjects, e.g. at high critical flicker frequencies (CFF).     

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m^-2 without city noise; (2) a calculating task on a VDT with luminance of 20 cd m^-2 without city noise; (3) a calculating task on a VDT with luminance of 90 cd m^-2 with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m^-2 with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the highluminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.     

Steady-state accommodation response and VDT screen conditions

Steady-state accommodation response was measured for seven different visual display terminal (VDT) screen conditions and a hard-copy control condition. The screen conditions included variations in screen polarity, contrast and chromatic characteristics of the text and background. Accommodation response was measured for seven young subjects using a free-space infrared optometer, the Canon Autoref R-1. The accommodation response was measured every 1.3 s over a period of 60 s for each test condition, and both the mean and standard deviation of the responses were derived. A small but significantly higher accommodation response was found for hard copy, blue-on-red and red-on-blue screen conditions compared with white-on-black, green-on-black and black-on-white screen conditions. Screen polarity and contrast had little effect on accommodation response for the black-and-white screen conditions. The variability of accommodation response showed little difference between test conditions. For short-term VDT screen viewing, the accommodation response appears to be relatively accurate and stable across a wide range of screen conditions.