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PubMed1989

Visual performance and subjective discomfort in prolonged viewing of chromatic displays.

Visual search and decision-making performance together with subjective fatigue were investigated over a 4-hr time block as a function of display foreground and background chromaticity using colors matched for brightness. Although some small differences in performance related to chromaticity were observed, these were not exacerbated over time. On the basis of the performance data obtained and the subjective reports, there was no support for the general recommendation to avoid the use of red and blue stimuli, either alone or in combination, in CRT displays.

Asthenopia↗
PubMed1990

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.

Adolescent↗
PubMed1991

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.

Accommodation, Ocular↗
PubMedDate not supplied

Long-term refractive and phoric changes in visual display unit (VDU) operators.

PURPOSE: This study assessed the phoric and refractive changes possibly caused by visual display unit (VDU) activity. METHODS: In a longitudinal trial nearly 6000 VDU operators received two ophthalmological examinations at intervals ranging from 34 to 43 months. The findings from the two examinations were correlated to VDU work (hours daily and years of VDU work), age and sex. RESULTS: Changes in the refractive state seemed to be mainly age-related. There was a slight tendency toward hyperopia (imbalance of latent hyperopia). CONCLUSIONS: In the analysis of ocular motility, the results show no worsening capable of causing a definitive change from heterophoria to heterotropia. Heterophoric subjects, however, tend to improve both with regular office work and with additional VDU activity.

Adolescent↗
PubMed1991

[Effects of video games on visual function in children].

Health effects of video games were examined with a questionnaire survey and an experimental study. In the survey, age, sex, playing time with video games in a day, viewing distance between the eyes and the television screen, subjective symptoms of eye strain, and changes of visual acuity were investigated in 2,034 male and 2,321 female primary school children. In the experimental study, the visual loads of a one-hour word processing task and a video game were compared with various indices, such as critical flicker fusion, near point distance, blinking counts, eyeball movement, pupillary reflex and subjective fatigue symptoms in ten healthy male college students. The results of this study were as follows: 1) The viewing distance between the eyes and the TV screen was shorter for video games than for watching TV programs. 2) The rate of complaints related to eye strain in children who played video games over 120 min per day was significantly higher than that of other children. 3) The eye movements during video games were more rapid and frequent than those during conventional VDT work. 4) A decrease in CFF value and an extension of near point distance and an increase in subjective fatigue symptoms were demonstrated for both the word processing task and the video game. No significant differences were observed between the above two experimental conditions. This suggests that the visual loads for video games are similar to those for VDT work. These findings suggest that regulating the playing times to 60 minutes or less per day is necessary to prevent negative health effects in children.

Asthenopia↗
PubMed1993

[Investigation of subjective symptoms among visual display terminal users and their affecting factors--analysis using log-linear models].

In order to evaluate factors affecting visual and musculoskeletal symptoms by visual display terminal (VDT) operation, a questionnaire survey was conducted among clerical workers in Chiba university. The results were as follows: 1) Of these workers, 81.9% engaged in VDT operation. For most of the subjective symptoms, the prevalence rates tended to increase with the degree of VDT use. 2) These complaints were combined to give visual and musculoskeletal symptom scores. Both of the scores were higher among females than males, and the musculoskeletal symptom score was significantly higher. No difference was found in regard to age. 3) Analysis using log-linear models was performed to evaluate the effects of sex and age. The results showed that the visual and musculoskeletal symptom scores were significantly higher among the workers operating VDTs for one or more hours per day than among those who did not operate them at all. Analysis of the effects of VDT workloads revealed that VDT use for five or more days per week significantly increased the prevalence rates of both symptoms. Their use for less than four days per week affected neither of the symptoms. With regard to operating time per day or length of VDT use, no differences were found. 4) This investigation suggested that the VDT workloads were not so heavy and that the effects on each symptom were minor among the subjects of the present survey. However, it is important that consideration be given to ensure that the workloads for workers who operate VDTs every day not be too heavy.

Adult↗
PubMed1995

Oculomotor responses with aviator helmet-mounted displays and their relation to in-flight symptoms.

Previous experiments have raised the possibility that abnormal oculomotor functioning could be the substrate for visual problems among aviators who use helmet-mounted displays. However, until the present investigation, no direct evidence linked the two. In our experiments, experienced Apache helicopter pilots, using the same helmet-mounted display that they use in flight, viewed Apache symbology and sensor imagery while we measured their accommodation and vergence eye movements in the laboratory. We found three circumstances that frequently occur in flight in which aviators with visual symptoms had different oculomotor responses than did asymptomatic aviators. Further work needs to be done to determine why symptomatic aviators respond differently from asymptomatic ones.

Accommodation, Ocular↗
PubMed1998

A comparison of seven visual fatigue assessment techniques in three data-acquisition VDT tasks.

We compared 7 methods of measuring visual fatigue--accommodation power, visual acuity, pupil diameter, critical fusion frequency (CFF), eye movement velocity, subjective rating of visual fatigue, and task performance--for their sensitivity to visual load. In the experiment, 10 participants performed a monitoring task at 2 viewing distances, read articles under 2 levels of screen contrast, and tracked visual targets at 2 different speeds. The same measurement techniques, excluding pupil diameter and eye movement velocity, were compared by extending the task time from 20 to 60 min with the same VDT tasks to test for possible improvement in sensitivity. The results indicated that sensitivities of accommodation power, visual acuity, and CFF were greatly improved by a longer task period, but these 3 measurement techniques did not distinguish among tasks. Pupil diameter, eye movement velocity, and subjective rating of visual fatigue were sensitive in differentiating tracking from reading and monitoring tasks. Eye movement velocity and subjective rating were sensitive to the changes in target velocity of the tracking task. Although task performance was not directly comparable to other measurement techniques, it helped to ensure that participants maintained the same performance level by devoting more resources to the high-load conditions. Actual or potential applications of this research include using some of these assessment techniques for the design of adaptive displays.

Accommodation, Ocular↗
PubMed1998

Effects of display resolution on visual performance.

The role of display resolution in visual information processing was investigated in 2 experiments. Experiment 1 examined the effects of 2 CRT conditions (resolutions of 60 and 120 dots per inch [dpi]) and a paper control condition (255 dpi) on proofreading speed and accuracy. The results showed that reading performance was significantly better in the paper condition than in the 2 CRT conditions. Experiment 2 examined the effects of 3 different CRT resolutions (62, 69, and 89 dpi) on eye movement parameters (fixation duration and number of fixations) in a visual search task. Further, search reaction times (RTs) and observers' ratings of visual fatigue were analyzed. RTs and fixation durations were significantly increased in the low-resolution condition (62 dpi) as compared with the high-resolution condition (89 dpi). The significant interaction between display resolution and time both for search RTs and fixation durations was taken as evidence for stronger fatigue in the low-resolution conditions. Additionally, the extent of visual fatigue correlates both with search RTs and eye movement parameters. This finding gives rise to the assumption that observers' responsiveness to effects of display resolution in terms of visual fatigue differs markedly. Actual or potential applications of this research include recommendations for the use of high-resolution displays (90 dpi and greater) to optimize visual performance, to make prolonged on-screen viewing more comfortable, and to avoid visual fatigue.

Asthenopia↗
PubMed1984

[An experimental study on the duration of a single spell of work on VDT (visual display terminal) performance].

The relation between work load and the duration of a single spell of work on VDT performance studied in an experimental word processing task. Nine healthy male college students performed 2-hour visual tasks under the following three sets of work conditions. In the first set, subjects performed VDT work for two hours without intermission. In the second set, subjects had a 10-minute intermission after a 1-hour task. In the third set, there was a 5-minute intermission after a 30-minute task. Critical flicker fusion, near point distance, subjective fatigue symptoms, heart rate, respiratory rate, blinking counts, electromyogram in upper limb and performance score were measured. Results are as follows. Decrease in critical flicker fusion, increase in near point distance and subjective fatigue symptoms appeared in all three sets of experimental conditions after two hour tasks. Increased slow wave components on electromyogram and increased errors in performance appeared after 60-minute or more tasks without intermission. Effects on the critical flicker fusion, near point distance, subjective fatigue symptoms, electromyogram, blinking counts and errors in performance were least in the third set. The results of this study suggest that in order to reduce operators' fatigue on VDT work of the conversation type, countermeasures such as shortening the duration of a single spell of work to less than 60 minutes and taking frequent short intermission are necessary.

Adult↗
PubMed1986

[Factors affecting subjective symptoms of VDT workers].

In 1983, 285 (male: 129, female: 156) VDT workers and 60 (male: 30, female: 30) control subjects were examined in order to detect the factors affecting the subjective symptoms of VDT workers. Biological information (for example: sex, age), life histories, information about VDT work, tests (for example: visual acuity), symptoms and interferences to daily life of VDT workers and control subjects were collected. The following results were obtained. Female VDT workers experienced more fatigue from commuting to work, stiffness in shoulders, distant blurred vision complaints of visual acuity and sum of the scores of ocular complaints than female control subjects. Only among female VDT workers, the longer the daily working hours, the greater were their ocular symptoms. A remarkable relationships were observed between psychological burden factors (for example: self-control of VDT work, sensation of excessive VDT work) and subjective symptoms of the VDT workers (both sexes). In particular, VDT workers who considered VDT work to be excessive had marked by greater subjective symptoms than those who did not.

Adult↗
PubMed1986

[An experimental study of work load on VDT performance. Part 2. Effects of difference in input devices].

Effects of the difference in input device on work load of VDT task were studied. The subjects of the experiment were eight healthy male college students (age: 21-22 yr) having a binocular vision of not less than 0.7 and no astigmatism or hyperopia. The test consisted of an experimental word processing task in which the subjects visually searched e's in given sequences of alphabetical letters displayed on the CRT and converted them to 5's through input device operation. As for experimental conditions, two kinds of input devices, namely, keyboard and lightpen were adopted and 1 h was provided as each operation time. Critical flicker fusion (CFF), near point distance, accommodation time, subjective fatigue symptoms, blinking counts, pupillary reflex, electromyogram in upper limb, neck and shoulder and performance score were measured. The results were as follows. Decrease in C.F.F. was observed in two experimental conditions during the process of operating time. Increments in complaints of subjective fatigue related to visual function were seen in the two experimental conditions after 1 h VDT task. A higher error rate in performance was observed in the subjects using the lightpen compared to the one using the keyboard. The frequency of both blinking and pupil-size changes were lower in the subjects using the lightpen compared to those using the keyboard. This suggests that the gaze time of the VDT screen with lightpen-condition is longer than that in keyboard-condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed1990

[An inquiry into the factors affecting the complaints of subjective symptoms in VDT operators].

In a study of VDT workers the relationship between 1) their general life condition and working environment and 2) their eye, shoulder, neck, arm, waist and back complaints and their psychological symptoms was investigated. The subjects of the study were (147 workers whose age ranged from 18 to 39 years, and who had used VDT for a monthly average of more than 40 h. The results were as follows: 1) For most of the symptoms, a tendency was observed for females to complain more than males and for younger workers to complain more than the older workers. Neck, shoulder, arm, waist and back complaints were more common than psychological symptoms. These physical complaints appeared to be the most common among VDT workers. 2) The occurrence of eye-related symptoms is related to items directly affecting sight. This reaffirms the importance of illumination for the visual system. 3) This investigation showed that a relatively good VDT working environment was secured for the subjects of the present study. It is important that consideration be given to labor management such as provision of rest period and supervision.

Adolescent↗
PubMed1992

[Changes in mental workload and fatigue during performance of a mental task. 1. An experiment in 8-h self-paced transcribing task].

The changes in mental workload and fatigue during a one-day transcribing task were examined by determining some subjective and physiological measures which reflect mental activity. With an interval of one week between the three test days, 12 male students rested and performed self-paced transcribing task with moderate and maximum effort for 8 h each. The subjects transcribed more characters in the task with maximum effort than with moderate effort. In both the morning and afternoon, adrenaline excretion increased and heart rate decreased with the lapse of time. In linear proportion to the total working hours, occipital midline beta-2 amplitude, subjective rating of tiredness and subjective symptoms of fatigue rose, but critical flicker values fell slightly in the task with maximum effort. It was inferred from these results that with lapse of working hours intellectual activity and feeling of fatigue increase and the level of arousal slightly declines. Hence, it was considered that mental workload becomes heavier and subjective feeling of fatigue increases as the working hours become longer.

Adult↗