Visual ergonomics of video-display-terminal workstations: Field measurements of luminance for various display settings

Electronic visual displays have shown a rapid technological evolution in the last two decades. With reference to the ergonomic requirements for video display terminal (VDT) workstations (ISO 9241), at an international level, attention is focused on the human–system interaction. With reference to visual ergonomics, the aim of this study is to assess luminance conditions through in-field measurements in order to evaluate: luminance and contrast ratios, luminance and contrast non-uniformities. The assessment was applied to widespread flat screen displays and repeated for fourteen combinations of Contrast–Brightness. The analysis carried out by the Authors shows the importance of realizing a simple and quick procedure to determine the performance levels of displays used in VDT workstations. The proposed assessment could be used as a practical tool for staff assigned to assess the risks arising from VDT use in the workplace within the Occupational Health and Safety Assessment Procedure.     

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.     

基于心电脉搏特征的视觉疲劳状态识别

为从生物医学信号角度检测和评估视觉疲劳，模拟VDT作业环境，对35位健康被试者进行1.5 h的VDT疲劳实验。使用MP425数据采集卡和LabVIEW构成的数据采集系统同步采集心电(ECG)和脉搏波信号，经信号预处理分析后，提取实验前后的ECG和脉搏波信号特征。研究结果表明，ECG和脉搏波信号特征在实验前后有较大变化，采用支持向量机法对实验前后的ECG脉搏组合特征进行分类，正确率可达100%。     

Objective evaluation of eye strain using measurements of accommodative oscillation

Accommodative oscillations occurring during eye strain induced by two different types of experimental visual search task—visual display terminal (VDT) work and conventional hard-copy (paper) work— were objectively measured using infrared optometry. The low-frequency component (0 to 1-5 Hz) of the accommodative oscillation was found to be significantly increased after the VDT work, but not after the paper work. At other frequencies there were no significant differences between the two work types and no significant effect of the task itself. In a questionnaire survey the subjects using the VDT complained more than the subjects given paper work of ocular symptoms such as eye strain and blurred vision. These results suggest that measurement of changes in accommodative oscillation, particularly the low-frequency component (0 to 15 Hz), may provide an objective parameter of eye strain.     

A longitudinal study of VDT work and health

A longitudinal study on the use of visual display terminals (VDTs) was conducted with questionaire data obtained 1981 and in 1987–1988 from a cohort of office workers. The use of VDTs became more widespread in these offices during the intervening time period, but the time spent by individuals working at VDTs showed no general increase. The data suggested that VDT use was related to the risk of developing eye discomforts and hand and wrist problems. For skin problems and headache, risks for VDT and non‐VDT users were fairly similar, but indications of increased risks were found for certain groups and situations. The risks of developing neck, shoulder, shoulder joint, or upper arm problems were high for both VDT and non‐VDT users, but there were, in this study, no convincing suggestions that these risks were higher for VDT users compared to nonusers.     

Study of the relationship between lacrimation and blink in VDT work

VDT (Visual Display Terminal) work generates various symptoms in operators' eyes such as strain, a sensation of dryness, the presence of a foreign body, and so on. Research suggests that lacrimal abnormality may be related causally to such symptoms. In this paper, the relationship between lacrimation (the secretion of tears) and the frequency of blink due to VDT work in health subjects and VDT workers with such symptoms, and consequent therapeutic methods, were studied. When lacrimation, BUT (Break-UP Time), and the frequency of blink before and after VDT work compared in the control subjects and VDT-operators, an essential difference was noted in experiment 1 the frequency of blink decreased only during VDT operation, and a decreasing tendency of lacrimation was also noted while lacrimation before operation was already less in the VDT group; no large variation was noted before or after VDT operation. The frequency of blink was relatively high during operation, and a decreasing tendency of BUT was noted, compared with that for control subjects. In experiment 2, lacrimation increased remarkably in four eyes (of two operators), and relief from the subjective symptoms was noted. However, BUT intactly reduced similarly before the use of a gelatin rod during the whole process. The insertion of a gelatin rod was consecutively carried out every two weeks for approximately eight months; the development of complications such as dacryosolenitis, etc., was not noted. From these results, it is considered that the insertion of a gelatin rod is clinically useful for VDT operators with decreasing lacrimation.     

Study of the relationship between lacrimation and blink in VDT work

VDT (Visual Display Terminal) work generates various symptoms in operators’ eyes such as strain, a sensation of dryness, the presence of a foreign body, and so on. Research suggests that lacrimal abnormality may be related causally to such symptoms. In this paper, the relationship between lacrimation (the secretion of tears) and the frequency of blink due to VDT work in health subjects and VDT workers with such symptoms, and consequent therapeutic methods, were studied. When lacrimation, BUT (Break-UP Time), and the frequency of blink before and after VDT work compared in the control subjects and VDT-operators, an essential difference was noted in experiment 1 the frequency of blink decreased only during VDT operation, and a decreasing tendency of lacrimation was also noted while lacrimation before operation was already less in the VDT group; no large variation was noted before or after VDT operation. The frequency of blink was relatively high during operation, and a decreasing tendency of BUT was noted, compared with that for control subjects. In experiment 2, lacrimation increased remarkably in four eyes (of two operators), and relief from the subjective symptoms was noted. However, BUT intactly reduced similarly before the use of a gelatin rod during the whole process. The insertion of a gelatin rod was consecutively carried out every two weeks for approximately eight months; the development of complications such as dacryosolenitis, etc., was not noted. From these results, it is considered that the insertion of a gelatin rod is clinically useful for VDT operators with decreasing lacrimation.     

Biomechanical evaluation of nursing tasks in a hospital setting

A field study was conducted to investigate spinal kinematics and loading in the nursing profession using objective and subjective measurements of selected nursing tasks observed in a hospital setting. Spinal loading was estimated using trunk motion dynamics measured by the lumbar motion monitor (LMM) and lower back compressive and shear forces were estimated using the three-dimensional (3D) Static Strength Prediction Program. Subjective measures included the rate of perceived physical effort and the perceived risk of low back pain. A multiple logistic regression model, reported in the literature for predicting low back injury based on defined risk groups, was tested. The study results concluded that the major risk factors for low back injury in nurses were the weight of patients handled, trunk moment, and trunk axial rotation. The activities that required long time exposure to awkward postures were perceived by nurses as a high physical effort. This study also concluded that self-reported perceived exertion could be used as a tool to identify nursing activities with a high risk of low-back injury.     

Frontal midline theta rhythm and eyeblinking activity during a VDT task and a video game: useful tools for psychophysiology in ergonomics

The necessity of psychophysiological research in ergonomics has gradually been recognized in Japan. In this paper, frontal midline theta rhythm (Fm-theta) and eyeblinking are recommended as tools in this field, especially for assessing workers' attention concentration, mental workload, fatigue, and interest during VDT work at the workplace and playing video games at home. In experiment 1, Fm-theta and eyeblink rates were measured in 10 Japanese abacus experts (Group E) and 10 normal students (Group C) during a visual search task with VDT. Memory load affected all measures. The amount of Fm-theta appeared more in Group E than Group C, but blink rate was lower in Group E than in Group C. As abacus experts have such highly developed skills in concentration, the result indicates that the amount of Fm-theta would be a good index of attention concentration in VDT workers. The second experiment was done with 10 schoolaged children as subjects during three visual tasks: video game, mental test and animation. Amounts of Fm-theta and the degree of blink inhibition were maximum while playing the video game, which all subjects reported they most preferred, and minimum while watching animation, which eight subjects reported to be most boring. An interesting task would seem to provoke Fm-theta and inhibit eyeblink activity. From these two experiments, Fm-theta and eyeblink rate would appear to be good indices of attention concentration and task pleasantness of a mental task using VDT.     

The effects of long-term VDT usage on the nature and incidence of asthenopic symptoms

An opportunity arose in 1985 to become involved in a transition of working practice from hard copy to VDT. Over a two-year period, 161 VDT users and 65 control subjects in the same office environment were regularly and routinely examined for symptoms of asthenopia. The analysis of data shows that there are no significant differences in type, number and frequency of the work-related symptoms between VDT users and non-VDT users. It appears that reporting of symptoms within the group may be random, although certain symptoms do appear more frequently than others. Additionally, it appears that there is a significant difference between male and female users in the frequency of symptom reporting.     

The effect of work-rest schedules and type of task on the discomfort and performance of VDT users

Consideration of the literature survey indicates that video display terminal (VDT) operators tend to have a high incidence of musculoskeletal problems, visual fatigue, and job stress. Although a number of ergonomic improvements in workstation design and work environment can help to reduce these problems, a proper work-rest schedule deserves consideration since it is easily applicable and inexpensive. The objective of this study was to compare the work-rest schedules for VDT operators considering data entry and mental arithmetic tasks. An experiment was conducted with 10 male college students as participants. The methodology included a discomfort questionnaire and performance measures. The independent variables were the work-rest schedule (60-minute work/10-minute rest, 30-minute work/5-minute rest, and 15-minute work/micro breaks) and the type of task (data entry and a mental arithmetic task). The results were analysed using multiple analysis of variance followed by separate analyses. The 15/micro schedule resulted in significantly lower discomfort in the neck, lower back, and chest than the other schedules for data entry task. The 30/5 schedule followed by 15/micro schedule resulted in the lowest eyestrain and blurred vision. Discomfort in the elbow and arm was the lowest with the 15/micro schedule for the mental arithmetic task. The 15/micro schedule resulted in the highest speed, accuracy, and performance for both of the tasks, compared with the 60/10 and 30/5 schedules. The data entry task resulted in significantly increased speed, accuracy, and performance, and lower shoulder and chest discomfort than the mental arithmetic task.     

The effect of work-rest schedules and type of task on the discomfort and performance of VDT users

Consideration of the literature survey indicates that video display terminal (VDT) operators tend to have a high incidence of musculoskeletal problems, visual fatigue, and job stress. Although a number of ergonomic improvements in workstation design and work environment can help to reduce these problems, a proper work-rest schedule deserves consideration since it is easily applicable and inexpensive. The objective of this study was to compare the work-rest schedules for VDT operators considering data entry and mental arithmetic tasks. An experiment was conducted with 10 male college students as participants. The methodology included a discomfort questionnaire and performance measures. The independent variables were the work-rest schedule (60-minute work/10-minute rest, 30-minute work/5-minute rest, and 15-minute work/micro breaks) and the type of task (data entry and a mental arithmetic task). The results were analysed using multiple analysis of variance followed by separate analyses. The 15/micro schedule resulted in significantly lower discomfort in the neck, lower back, and chest than the other schedules for data entry task. The 30/5 schedule followed by 15/micro schedule resulted in the lowest eyestrain and blurred vision. Discomfort in the elbow and arm was the lowest with the 15/micro schedule for the mental arithmetic task. The 15/micro schedule resulted in the highest speed, accuracy, and performance for both of the tasks, compared with the 60/10 and 30/5 schedules. The data entry task resulted in significantly increased speed, accuracy, and performance, and lower shoulder and chest discomfort than the mental arithmetic task.     

The influence of VDT work on musculoskeletal disorders

Relationships between visual display terminal (VDT) use and musculoskeletal problems were examined in a group of 353 office workers, using data from medical and workplace investigations as well as questionnaires. There were no general differences between VDT and non-VDT users as to the occurrence of muscle problems. Combinations of specific VDT work situations such as data entry work or work with a VDT for more than 20 h/week and the presence of some other factors were, however, associated with excess risks of certain muscle problems. The extraneous factors involved in the definitions of such risk groups were: use of bifocal or progressive glasses at a VDT; stomach-related stress reactions; limited rest break opportunity, repetitive movements; non-use of lower arm support; and possibly the vertical position of the keyboard; and presence of specular glare.     

Effects of VDT resolution on visual fatigue and readability: an eye movement approach

The effects of VDT resolution on visual fatigue and readability were studied. Two kinds of displays with different resolutions (1664 x 1200 pixels and 720 x 350 pixels) and fonts were used. In the first experiment, the subjects read from each display for 1 h to induce fatigue. Reading speed and blink rate while reading were measured. Eye movements during visual smooth pursuit tracking tasks were studied before and after reading; quantitative scoring of eye movement performance showed no significant changes. In the second experiment, readability tests with three different character sizes on both displays were conducted and resulting reading eye movements were analysed. For readability of sufficiently large characters, no significant difference between the high and the standard VDT could be detected. However, for very small characters, higher resolution improved readability.     

Quantitative methods for detecting cerebral infarction from multiple channel EEG recordings

EEG has been known to be non-stationary and time varying. Time–frequency representation (TFR) is a proper tool for such non-stationary signals. In the present paper, TFR-based quantitative methods that can translate complicated and subjective waveform-based EEG analysis into objective measures are introduced to characterize EEG recorded from normal subjects and cerebral infarction (CI) patients. Relative frequency band energy (RFBE) is computed from time–frequency plane for the five subbands: delta, theta, alpha, beta and gamma. Moreover, we propose the Shannon entropy (SE) of TFR to detect the difference in EEG for the two kinds of subjects. Finally, the temporal evolutions of these quantitative parameters are presented to trace EEG changes. The experiment results show that CI results in the RFBE changes of the five rhythms; however, the RFBEs of some rhythms have stronger association with CI. Increase in EEG SE of CI patients is obvious. The time evolutions of RFBE and SE as valuable objective measures can be displayed in real time and be used as helpful references in detection and monitoring of CI.     

Prediction of slips: an evaluation of utilized coefficient of friction and available slip resistance

The purpose of this study was to investigate the relationship between measures of floor surface slip resistance and an individual's peak utilized coefficient of friction (COFU) on the probability of a slip occurring during level walking. Video, kinematic and ground reaction force data were recorded simultaneously as subjects walked at a self-selected speed during conditions of normal and reduced floor surface slip resistance. Peak COFU during weight acceptance was calculated and the available floor surface slip resistance was measured using the variable incidence tribometer (VIT). Separate logistic regression analyses identified that knowledge of the available slip resistance (as measured by the VIT) in combination with an individual's peak COFU allowed for greater accuracy in classifying slip outcomes (89.5%; p = 0.004), while knowledge of only the available slip resistance reduced the accuracy of categorization to 78.9% (p = 0.021).     

软件项目风险管理中风险分析方法的研究

对软件项目风险分析中的定性分析方法和定量分析方法进行了讨论，提出了定性分析与定量分析相结合的方式对软件项目中已识别的风险进行分析的方法，并且在分析过程中考虑了风险偏好性的影响。     

抑郁症静息脑电的小波包节点功率谱熵分析

头皮脑电(EEG)信号反映了大脑皮层神经元细胞群自发性节律性的电生理活动,含有丰富的生理与病理信息,是临床脑神经与精神疾病诊断的重要依据.针对抑郁症的研究和诊断中缺少客观有效的量化参数和指标的状况,提出一种基于小波包分解节点重构信号的功率谱熵值(记为W值)的脑电信号分析方法,并利用此方法对静息态的脑电信号进行计算和分析.实验和分析结果表明:抑郁症患者脑电信号S32节点(频率24~32 Hz)的熵值(置信区间[0.0129,0.0176])在部分脑区显著大于正常健康人(置信区间[0.0246,0.0303]),显示抑郁症病人快波节律的能量分布存在弥散性,符合现在关于抑郁症患者自我调节能力减弱的发病机制.对结果进行了T检验统计分析,证明了这种辨别方法的准确性和可行性,将为抑郁症疾病检测诊断提供有效的量化物理指标.     

Job design predictors of stress in automated offices

The effects of job control, job content, demands and career/future concerns on stress outcomes were tested in a population of video display terminal (VDT) users that were categorized as clericals, managers/supervisors and professionals. It was found that career/future concerns were consistent contributors to stress outcomes across job categories, but job control - which was hypothesized as a central stressor - did not contribute to the stress outcomes. Analyses performed within each of the three job categories demonstrated that different job elements contributed to the stress outcomes. A proposed model that denned job control as the central job element through which other job features (i.e. job content, demands and career/future concerns) produced stress outcomes was verified in only one of the four analyses for mood disturbances among professional VDT users.