Marino Menozzi

CRT versus LCD: A pilot study on visual performance and suitability of two display technologies for use in office work

Cathode ray tube (CRT) display and liquid crystal display (LCD) were compared for their suitability in visual tasks. For this purpose visual performance was assessed by means of a search task carried out using both displays with different levels of ambient light. In addition, suitability was rated subjectively by users of visual display units (VDUs). Error frequency for search tasks carried out using LCD were significantly smaller when compared to error frequency for tasks at CRT. LCD gave rise to 34% less errors than did CRT. Reaction time in search task was found to be significantly shorter using LCD when tasks were carried out in darkness. Subjective rated suitability of LCD was scored twice as high as suitability of CRT. Results indicate that LCD used in this experiment may give better viewing conditions in comparison to CRT display.

Direction of gaze and comfort: discovering the relation for the ergonomic optimization of visual tasks.

Perceived exertion caused by the extraocular muscles was assessed as a function of the direction of gaze and recorded in 114 subjects using a psychometric method. The results confirm statements in the literature that maximum comfort is achieved when gaze is aimed downwards. We found mi correlations between perceived exertion and age or viewing distance. The relationship is relevant to ergonomics, for example in tens lining and workplace layout.

Can movement parallax compensate lacking stereopsis in spatial explorative search tasks

Abstract In an explorative task subjects were asked to track a line presented in combination with other confusing lines on a 3D display. 24 subjects performed the explorative task under three depth cue conditions which were: stereopsis, movement parallax or a combination of stereopsis and movement parallax (stereo and parallax). Task performance was assessed by recording completion time and correctness of answer. The combination of stereopsis and movement parallax gave rise to highest percentage of correct answers (84%), followed by the condition where movement parallax was the only depth cue (80%). Percentage of correct answers in both conditions was found to be significantly higher than it was in the condition with stereopsis (60%). Mean completion time was about the same in the stereo and parallax condition and the stereopsis condition. Compared to the movement parallax condition both means were significantly decreased. Accuracy in completing the task was found to be similar in 3D displays enabling movement parallax and in 3D displays presenting stereoscopic images.

Visual ergonomics of head‐mounted displays

Head-mounted displays (HMDs) are increasingly used in the field and in the laboratory. Prolonged use of HMDs requires their ergonomics to be optimized in order to reduce discomfort. Among factors causing visual load are the physical/optical properties of eyepieces used in HMDs. Many HMD eyepieces are adjusted manually to fit the individual requirements of the user. Proper adjustment of the eyepieces requires some knowledge of visual ergonomics. Additionally, in order to enable comfortable viewing, restrictions on the visual information presented in HMDs, such as the motion of objects in virtual depth, must be considered. Visual performance and therefore visual load depends on the display technology used in HMDs.

Training in ergonomics at VDU workplaces

In an internal campaign, a large Swiss company carried out an instruction programme with employees concerning ergonomics at a VDU. Before and after this campaign, the existing conditions were recorded regarding ergonomics at the VDU workplace. At the same time, complaints, as well as individual knowledge and interest in ergonomics, were recorded. Based on the information at hand, it can be assumed that the campaign improved the existing conditions of ergonomics, as well as the self-responsibility on the part of those involved. A compilation of the work involved indicates that a training course with the objective of influencing ergonomics at the place of work was cost effective.

Applying the Ishihara test to a PC-based screening system

Abstract Aim: A commonly used method to examine the ability of the visual system to discriminate colours is based on isochromatic plates, such as the Ishihara plates. This article will introduce a computer-based method to determine red–green colour deficiencies based on presenting Ishihara plates using a CRT monitor. Method: The spectral emission of the reflected daylight of the plates was compared with the spectral emission of the plates presented on a CTR monitor. The screening efficiency of the Ishihara plates was assessed by testing 10 subjects with normal and 10 subjects with abnormal colour vision, using the Ishihara plates and using the computer-based approach. Results: It was experimentally shown that despite the differences between the spectral emission of the CRT monitor and the reflected daylight of the Ishihara plates, the computer-based method discriminates subjects with colour deficiencies from subjects without colour deficiencies. Conclusions: Using a CRT monitor for screening purposes, a reduced number of Ishihara plates is recommended to assess colour vision. The suggested method uses nine instead of 15 plates and a criteria of two not correctly detected plates to determine colour deficiency.

Effect of Subjective and Objective Workload on Asthenopia at VDU Workplaces

An ergophthalmological tool has been developed to investigate effects of subjective and objective workload on work-related visual complaints (asthenopia). In field studies on different visual display unit (VDU) workplaces effects of objective and subjective workload, work intensity, and work breaks (5-9 min/hour) could be found. It could be shown that during the first hours of VDU work, asthenopic complaints have the tendency to follow effective workload. With increasing working time the effect of a general and visual fatigue overlaps other reported visual complaints in the majority of cases.

Visual Performance in Augmented Reality Systems for Mobile Use

Users of augmented reality (AR) must direct their attention toward real world as well as artificial information. The authors investigated some aspects of interference between the 2 sources of information that affect performance in completing a visual search task. The search task was carried out under 3 different conditions, 2 of them as found in AR in mobile systems. Participants were asked to detect a target that was superimposed on a background. Target and background were presented on a screen subtending a rectangular area of 55� � 43� (horizontal � vertical). The target appeared at 6 different locations on the screen. A video recording of a car drive served as the background. In 1 condition, the recording was replayed continuously. Static images of the record were sampled at 5-sec intervals and replayed as background in another condition. A uniform gray background served as a baseline.

Visual Information Processing in Augmented Reality: Some Aspects of Background Motion

We assessed discomfort, time and number of saccades for reading a text superimposed to a moving background. When background moved in the main directions of reading (left to right or top to bottom), discomfort was rated significantly lower than when background moved in the opposite directions. Neither time for reading nor number of saccades are affected by background motion. We therefore conclude that increased arousal might be responsible to cope with effects of background motion, resulting in an increased stress and rising discomfort when background moves opposite to main directions of reading. The findings suggest that reading in Augmented Reality for mobile use must be considered as a robust process. However, load may be increased and cause complaints in a prolonged reading task.

A tool for viewpoint-dependent graphical simulation of 3D space

Abstract Accurate space perception within 3D display systems could be dependent on the real observers viewpoint relative to the displayed 3D space. In this article, a stereoscopic display system is presented, which achieves viewpoint-dependent graphical simulation of space in real time. The concept, function and construction of the equipment is outlined. Emphasis is placed on the method used to measure the observers viewpoint. The performance of the display system with respect to the capabilities of the human visual system is discussed and finally, a brief description of an experiment to quantify observer performance is given.