Effects of task duration, display curvature, and presbyopia on physiological and perceived visual fatigue for 27??? desktop monitors

Department of Human and Systems EngineeringWith the advancement of display technologies, more diverse display products are available around us. VDT (Visual Display Terminal) tasks are, however, associated with various visual fatigue symptoms that can reduce work efficiency and task performance. Such results can be more severe for older individuals with diminished visual abilities, which typically start around the age of 40. However, studies on visual fatigue of older individuals are relatively fewer than those for younger individuals. Though, proper work-rest schedules are deemed to reduce visual fatigue, workers have difficulty in taking rest breaks due to many reasons. It is expected that a real-time rest reminder will be effective because the time to onset of visual fatigue can vary as visual fatigue is affected by many factors including individual and task characteristics. Curved displays provide relatively even viewing distances across their display surface for the center viewer than flat displays, which could benefit viewing experience while reducing visual fatigue. Indeed, some studies on display curvature demonstrated that curved displays are more effective than flat displays in terms of task performance, visual fatigue, and preference. Previously, various physiological measures (e.g. accommodation amplitude and near point accommodation) were considered as indices of visual fatigue. Using these measures to predict visual fatigue in daily life are, however, not practical because of difficulties in measuring and/or needs for high-cost equipment. The aims of the current study were 1) to examine the effects of task duration, display curvature, and presbyopia on physiological and perceived visual fatigue and display satisfaction associated with performing proofreading tasks on 27??? displays, and 2) to develop a prediction model for visual fatigue using pupil- and bulbar conjunctiva-related measurements which can be easily obtained in daily life. A total of 64 participants (32 for each age group) performed a 1-hr proofreading task. The current study considered task duration (within-subjects0, 15, 30, 45, and 60 min), display curvature (between-subjects600mm, 1140mm, 4000mm, and flat) and age group [between-subjectsyounger (20-35 yrs) and older (45-60 yrs)] as independent variables. Pupil diameter, bulbar conjunctival redness, perceived visual fatigue [measured in ECQ (Eye Complaint Questionnaire) scores], and display satisfaction were obtained every 15 minutes, while CFF (Critical Fusion Frequency) was obtained pre and post the 1-hr proofreading task. The rear-projection environment was comprised of 27??? curved rear screens, a beam projector, and the Warpalizer software. Environmental factors that can affect visual fatigue were controlled. An eye tracking system, a digital camera, and a flicker fusion system were used to measure physiological measures of visual fatigue, and a series of questionnaires were used to measure perceived visual fatigue and satisfaction of display. 3-way ANOVA was used to examine how 3 independent variables and their interactions affected each of 5 dependent variables. Four methods were considered in developing prediction models for visual fatigue and display satisfaction, and the developed models were compared in terms of predictive accuracy. The results showed that over the 1-hr task, pupil diameters decreased (5.1%), bulbar conjunctival redness increased (18.8%), CFF thresholds decreased (0.94%), and ECQ scores increased (207%), all indicating an increase in visual fatigue. Even with a 15 min of VDT task, visual fatigue increased significantly. At the 1140mm curvature, pupil diameters were the largest, indicating less visual fatigue, and the display satisfaction of the older group, though not significant, gradually increased over the 1-hr task, indicating a less increase in visual fatigue. Display satisfaction was not affected by any independent variables. In terms of predictive accuracy of visual fatigue, the artificial neural network model was the best followed by the 3rd degree polynomial regression model. The results of this study can be utilized when scheduling work-rest, determining a better display curvature for 27??? displays, and predicting visual fatigue in real time to notify the time to take a rest.ope

Curved Displays, Empirical Horopters, and Ergonomic Design Guidelines

Department of Human Factors EngineeringVisual display products should be comprehensively evaluated from the perspectives of productivity, safety, and well-being. Curved display products are known to provide advantages. Although previous studies found that curved displays increase visual task performance, reduce visual fatigue, and improve the watching experience, these studies did not comprehensively examine the effects of display curvature. Moreover, they used low-fidelity curved screens that may not effectively reflect actual curved displays. The purpose of this thesis was to develop ergonomic design guidelines for determining appropriate display curvatures, considering the productivity, safety, and well-being of visual display terminal (VDT) users. Two studies on monitors and one study on TVs were conducted for this goal. In Study 1, the effects of the display curvature, display zone, and task duration on visual task performance and visual fatigue during a visual search task on a 50-inch multi-monitor were investigated. In Study 2, the effects of the display curvature and task duration on visual task performance, visual fatigue, and user satisfaction during a proofreading task on a 27-inch monitor were investigated, and the associations between ergonomic evaluation elements were then examined. Prediction models of visual fatigue and user satisfaction were subsequently developed. In Study 3, the effects of the display curvature, viewing distance, and lateral viewing position on presence, visual comfort, and user satisfaction during a TV watching task on a 55-inch TV were examined, and the importance of six viewing experience elements affecting user satisfaction was revealed. Finally, ergonomic design guidelines for curved displays were suggested. Based on the results of studies 1 and 2, an appropriate rest-break time was ecommended, taking into account visual task performance and visual fatigue. Study 1 examined the effects of the display curvature (400 R, 600 R, 1200 R, and flat), display zone (five zones), and task duration (15 and 30 min) on legibility and visual fatigue. A total of 27 participants completed two sets of 15-minute visual search tasks with each curvature setting. The 600 R and 1200 R settings yielded better results compared to the flat setup regarding legibility and perceived visual fatigue. Relative to the corresponding center zone, the outermost zones of the 1200 R and flat settings showed a decrease of 8%???37% in legibility, whereas those of the flat environment showed an increase of 26%???45% in perceived visual fatigue. Across curvatures, legibility decreased by 2%???8%, whereas perceived visual fatigue increased by 22% during the second task set. The two task sets showed an increase of 102% in the eye complaint score and a decrease of 0.3 Hz in the critical fusion frequency, both of which indicated a rise in visual fatigue. To sum up, a curvature of around 600 R, central display zones, and frequent breaks were recommended to improve legibility and reduce visual fatigue. Study 2 examined the effects of the display curvature and task duration on proofreading performance, visual discomfort, visual fatigue, mental workload, and user satisfaction. Fifty individuals completed four 15-min proofreading tasks at a particular curvature setting. Five display curvatures (600 R, 1140 R, 2000 R, 4000 R and flat) and five task durations (0, 15, 30, 45, and 60 min) were incorporated. The mean proofreading speed at its highest when the display curvature radius was equal to the viewing distance (600 R). Across curvatures, speedaccuracy tradeoffs occurred with proofreading, as indicated by an increase of 15.5% in its mean speed and a decrease of 22.3% in its mean accuracy over one hour. Meanwhile, the mean perceived visual discomfort, subjective visual fatigue, and mental workload increased, by 54%, 74%, and 24% respectively, during the first 15-min of proofreading. A decrease of 0.4 Hz in the mean critical fusion frequency during the first 15 min and a reduction in the mean blink frequency also indicated increases in visual fatigue and mental workload. The mean user satisfaction decreased by 11% until 45 min. A segmented regression model, in which perceived visual discomfort was used as a predictor, attributed 51% of the variability to visual fatigue. To sum up, a curvature of 600 R was recommended for speedy proofreading. Moreover, the breakpoint was observed be flexible, depending on VDT task types. These findings can contribute to determining ergonomic display curvatures and scheduling interim breaks for speedy but less visually fatiguing proofreading. Study 3 examined the effects of the display curvature, viewing distance, and lateral viewing position on the TV watching experience. The watching experience was assessed regarding the spatial presence, engagement, ecological validity, negative effects, visual comfort, image quality, and display satisfaction. Four display curvatures (2.3 m, 4 m, 6 m, and flat), two viewing distances (2.3 m and 4 m), and five lateral viewing positions (0 cm, 35 cm, 70 cm, 105 cm, and 140 cm) were evaluated. Seven pairs of individuals per curvature watched ten 5 min videos together, each time at a different viewing distance and lateral viewing position. Spatial presence and engagement increased when the display curvature approached the given viewing distance. Regardless of display curvature and viewing distance and TV watching experience factors, except negative effects, were degraded at more lateral viewing positions. Engagement could effectively explain the display satisfaction. These findings can contribute to enhancing TV watching experiences by recommending specific levels of display curvatures, viewing distances, and lateral viewing positions, as well as providing information on the relative importance of each watching experience element. This work suggested ergonomic design guidelines for curved displays. In Study 1, a curvature of approximately 600 R, central display zone, and frequent breaks were proposed to improve legibility and reduce visual fatigue during visual search tasks at the viewing distance of 500 mm. In Study 2, a curvature radius of 600 R and a minimum 15-minute break interval were proposed for a speedy proofreading task, at the viewing distance of 600 mm. In Study 3, a display radius of curvature similar to the viewing distance was recommended to improve the viewing experience. These results support that a curved display is ergonomically more beneficial when the display curvature approaches the empirical horopter. A relatively short 15-minute rest-time interval was suggested, considering the decrease of task accuracy and the increase of visual fatigue in studies 1 and 2. Two regression models were selected in Study 2 regarding predictive accuracy. They accounted for 70.4% of subjective visual fatigue variability and 60.2% of user satisfaction variability. Although this work was performed using relatively higher-fidelity mock-ups than previous studies, it is necessary to verify the findings with actual curved display products in the future. Furthermore, various tasks (e.g., word processing, graphics design, and gaming) and personal characteristics (e.g., presbyopia, gender, visual acuity, and product experience) should be considered to generalize the results of this thesis. These results can contribute to determining the ergonomic display curvature in consideration of productivity, safety, and well-being, and prioritizing elements of the visual fatigue and user satisfaction resulting from VDT work.ope