Evaluation of Shoulder Muscular Fatigue Induced During VDT Tasks

This study was designed to evaluate localized muscular fatigue induced during visual display terminal (VDT) tasks. In the experimental paradigm used, electromyography (EMG) signals were not recorded during the VDT task but during isometric contractions in which the load imposed on the shoulder muscle was kept constant. The change in mean power frequency (MPF) and the root mean square values of EMG signals with time were explored. The correspondence between these measures and the psychological rating of localized muscular fatigue also were examined. The effectiveness of the experimental paradigm and of the measures used for evaluation of localized muscular fatigue are discussed. MPF measured during isometric contraction was found to be a sensitive measure of localized muscular fatigue.     

Visual comfort in using different VDT screens

In order to meet the goal of user comfort of information displays, visual problems of video display terminal (VDT) work were studied through the analysis of visual functions in two experiments. Eye movement analysis, in Experiment 1, revealed that VDT operators had to move their eyes 2.5 times faster than traditional clerical workers. Lens accommodation, pupil size, and subjective visual comfort were investigated in Experiment 2. A significant correlation was found between the velocity of lens accommodation and the subjective visual comfort while viewing seven different displays (r = .809). A positive‐type cathode‐ray tube (CRT), which has dark characters on a light background, was ascertained to be the most appropriate display type, while working with a liquid crystal display (LCD) was considered to be the least visually comfortable, with the lowest accommodative velocity.     

Visual evoked potentials as indicators of the workload at visual display terminals

No physiological correlates are known for visual fatigue produced by prolonged viewing of visual display terminals (VDTs). The primary aim of the present study was to find a physiological correlate of a performance measure which is related to fatigue. The assumption was that a change in the state of fatigue expresses itself in fluctuations of accommodation. If indeed variations in accommodation are indicative of fatigue, then visual evoked potentials (VEPs) might be used for the objective estimation of fatigue, because pattern EPs are highly sensitive to the quality of the retinal image.

In a realistic visual task, the VEP to pattern onset and the performance to a binary task are recorded simultaneously. Both indicators of fatigue, the amplitude of the VEP and the reaction time, proved to be sensitive to the workload of the task. If accommodation effort was increased, then reaction time increased and VEP amplitude decreased. Thus, VEPs are an indicator of the workload of a visual task. This allows comparison of the fatiguing effects of various office settings on the basis of the pattern EP of a particular subject. However, because VEP amplitude and reaction time do not have the same relation amongst subjects, the pattern EP cannot be used for inter-individual comparison.     

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.     

Pupil responses to continuous aiming movements

Pupillary response is associated with perceptual and cognitive loads in visual and cognitive tasks, but no quantitative link between pupil response and the task workload in visual−motor tasks has been confirmed. The objective of this study is to investigate how the changes of task requirement of a visual−motor task are reflected by the changes of pupil size. In the present study, a simple continuous aiming task is performed and the task requirement is manipulated and measured by Fitts’ Index of Difficulty (ID), calculated for different combinations of the target size and movement distance. Pupil response is recorded using a remote eye-tracker. The results show that event-triggered pupil dilations in continuous aiming movements respect Fitts’ Law, such that higher task difficulty evokes higher peak pupil dilation and longer peak duration. These findings suggest that pupil diameter can be employed as a physiological indicator to task workload evoked by the task requirement in visual−motor tasks.     

Influence of social presence on eye movements in visual search tasks

Abstract

This study employed an eye-tracking technique to investigate the influence of social presence on eye movements in visual search tasks. A total of 20 male subjects performed visual search tasks in a 2 (target presence: present vs. absent) × 2 (task complexity: complex vs. simple) × 2 (social presence: alone vs. a human audience) within-subject experiment. Results indicated that the presence of an audience could evoke a social facilitation effect on response time in visual search tasks. Compared with working alone, the participants made fewer and shorter fixations, larger saccades and shorter scan path in simple search tasks and more and longer fixations, smaller saccades and longer scan path in complex search tasks when working with an audience. The saccade velocity and pupil diameter in the audience-present condition were larger than those in the working-alone condition. No significant change in target fixation number was observed between two social presence conditions.

Practitioner Summary: This study employed an eye-tracking technique to examine the influence of social presence on eye movements in visual search tasks. Results clarified the variation mechanism and characteristics of oculomotor scanning induced by social presence in visual search.     

Effects of task characteristics on unimanual and bimanual movement times

Fitts' law cannot be used to predict movement times (MTs) of bimanual tasks since no empirical relationships associating task difficulty and bimanual MT have been demonstrated yet. Development of a ‘bimanual task difficulty index’ has been challenged by the complex patterns of coordination involved in simultaneously performing two tasks, one with each hand, under a control system with limited visual and attentional resources. To address this fundamental issue in human motor performance, bimanual object transfers with the left and right hands to targets of various precision requirements and separated by different distances were studied in six healthy subjects. Visual resource allocation during task performance was used to identify ‘primary’ and ‘secondary’ hand movements in bimanual tasks. While the primary movement was similar to a unimanual movement, the secondary MT varied with its own, as well as the contralateral hand's task constraints. These results, which were stable and consistent across six subjects, provide preliminary evidence that visual behaviour, indicating closed-loop control, can be used to systematically derive bimanual MTs.

Practitioner summary: A simple extension of Fitts' law cannot be used to predict movement times (MTs) of bimanual tasks since there is no consensus on the definition of a ‘bimanual task difficulty index’ in the literature. In this paper, we have approached this problem by using visual resource allocation patterns to systematically derive bimanual MTs.     

基于眼动数据的视觉疲劳检测方法研究

视觉疲劳的产生不仅会导致工作效率低下、视力降低,甚至可能导致很多意外伤害.如何简便、快速地检测视觉疲劳是亟需解决的课题.提出一种利用特殊字搜索并结合阅读任务来对视觉疲劳进行快速检测的方法.测试者需在所提供的阅读材料中通过扫视行为寻找出文内的特殊字符,同时完成相应的阅读理解任务.实验在Tobii X230眼动仪监测下完成.系统记录任务完成过程中的瞳孔直径比、兴趣域个数等眼动数据信息,并采用BP神经网络对用户的视觉疲劳状态进行判定.基于10位测试者的实验结果表明,分类精度达到了95.2%,证实了该方法的有效性.     

Effects of virtual lighting on visual performance and eye fatigue

This study is designed to determine whether differences in eye fatigue and visual performance can be shown under varying virtual industrial lighting conditions. It is based on the results of studies of more traditional video display terminal (VDT) tasks reported in the literature. One experiment was designed to determine if the effects of virtual lighting on eye fatigue and visual performance in a simulated virtual industrial environment are similar to some other VDT tasks with varying luminance contrast. Results of a test of 20 participants in a vigilance task show that there is a significant difference in performance and eye fatigue in the virtual environment with varying virtual light conditions. These results may help designers see that performance in some virtual “lighting” conditions, for some tasks, is consistent with that in the real. However, due to the difficulties of determining the appropriate virtual objects to be considered for the luminance measures, additional research is needed to be able to generalize the results to other industrial training scenarios. A second experiment was intended to test for the luminance decrement in a VDT that was shown in recent literature. The results would have potential implications for the experiment that included a vigilance task. However, the results showed that the luminance decrement demonstrated in recent literature did not occur. These results suggest that the equipment used in the present experiments should not cause difficulty in interpreting the results of the vigilance task. © 2002 Wiley Periodicals, Inc.     

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.     

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.     

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%。     

Visual Efficiency and Fatigue during the Afternoon Shift

Abstract

For one week, four times a shift, six female machinists were tested for visual fatigue. Three methods were used: convergence and accomodation reading, blink rate, and visual information transfer efficiency. Decrement of convergence and accommodation performance, as well as a higher number of faults and a lengthening of reading time, were found. Increase of blink rate was another result. The importance of the first two methods is stressed as such a diagnosis takes only a short time and can be done directly at the work-place, giving a reliable picture of the visual well-being of the subject     

Can eye-tracking data be measured to assess product design?: Visual attention mechanism should be considered

Eye tracking probes user's perception of real-time reaction to products, while conventional methods (i.e. interviews, focus group, questionnaires and so on) have generally failed because they depend on users' willingness and competency to describe how they feel when they are exposed to a product. Two tasks were designed to explore the indexes of eye movement that can reflect user experience of product, and analyse the attention captured by product attributes and goal-oriented. In task one, participants just browsed two smart phone pictures and evaluated the whole user experience. Binary choices were used in task two to ask participants to select the smart phone picture with higher user experience and then click the mouse. The results showed that in the browsing task, participants had shorter time to first fixation for the smart phone picture with higher level of user experience than the lower. And pupil dilated significantly when participants browse smart phone picture with lower level of user experience. In goal-oriented task, participants' attentions were dominated by visual perception of task driven, mainly reflected on longer fixation time and larger pupil diameter when looking at the smart phone with higher level of user experience. These results support the notion that we cannot assess product design just by several eye-movement indexes without considering the effects of visual attention mechanism.Relevance to industryThe appearance of product plays an important role to attract user's attention and stimulate their intention to experience. And vision is the main channel for users to obtain product information. Hence a thorough research on the inherent mechanism of vision perception can provide technical support for product designers, which in turn can attract more consumers to experience the product, even buy it. Moreover, the seller can find out the real buyers and predict their desired products by tracking user's eyes.     

Assessment of visual fatigue caused by stereoscopic disparity based on multimodal measurement

Given the prevalence of visual fatigue induced by stereoscopic display, research on the neural mechanism of visual fatigue was limited. The goal of this study was to investigate the effect of stereoscopic display with different horizontal disparities on visual fatigue based on subjective questionnaire, ophthalmological parameters, eye movement and electrocardiogram (ECG). Subjects felt more headache, uncomfortable and dry eyes after watching 70-minute enhanced 3D display with larger negative disparity than normal 3D display. Meanwhile, visual function tear film break-up time (TBUT) reduced, microsaccade mean pupil diameter (MMPD) increased and heart rate variability (HRV) changed more significantly after watching enhanced 3D display. Overall, these results demonstrated that enhanced 3D display had a better sense of immersion, but it induced more visual fatigue significantly than normal 3D display.     

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.     

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.     

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.     

A neuroergonomic approach to evaluating mental workload in hypermedia interactions

Neuroergonomics could provide on-line methods for measuring mental effort while the operator interacts with hypermedia. We present an experimental study in which 28 participants interacted with a modified version of an existing Spanish e-commerce website in two searching tasks (Goal oriented shopping and Experiential shopping) that demand different amounts of cognitive resources. Mental workload was evaluated multidimensionally, using subjective rating, an interaction index, and eye-related indices. Eye movements and pupil diameter were recorded. The results showed visual scanning behaviour coincided with subjective test scores and performance data in showing a higher information processing load in Goal oriented shopping. However, pupil diameter was able to detect only the variation in user activation during the interaction task, a finding that replicates previous results on the validity of pupil size as an index of arousal. We conclude that a neuroergonomics approach could be a useful method for detecting variations in operators’ attentional states.

Relevance to industry

These results could provide important information for the development of a new attentional screening tool for the prevention of accidents in several application domains.