Effects of display technologies on operation performances and visual fatigue

Highlights

• The effects of VR display technology, task complexity, and use time on operation performances and visual fatigue were discussed.

• Display technology seems not affect the operation performances and had no significant effects on subjective visual fatigue and near-point accommodation (NPA) but affected critical fusion frequency (CFF) significantly.

• Subjective and objective measurements showed that visual fatigue was affected by use time.

• The effect of VR display technology on visual fatigue was observed by measuring CFF but did not find by subjective and NPA measurements.

Abstract

The use of 3D stereoscopic display technology in all aspects of life has attracted considerable research attention. However, only few studies have simultaneously considered the effects of stereoscopic display technologies on visual fatigue and operating performances. This study with 36 participants (50% females; mean age = 23.17 years, SD = 3.3) analyzed the effects of display technologies, task complexity, and use time on operation performances, subjective and objective visual fatigue. Results indicated that display technology did not significantly affect the operation performances, whereas task complexity did. However, no interaction took place between them. Display technology had no significant effects on subjective visual fatigue and near-point accommodation (NPA) but affected critical fusion frequency (CFF) significantly. Use time had significant effects on both subjective and objective visual fatigue.

Introduction

People from all walks of life need to be trained, particularly in highly risky, complex, and costly operations. Therefore, a set of effective training methods should be proposed to reduce training costs and risks, as well as enhance operational performance. Given the advance of computer technologies and the reduced cost of computer hardware and software in recent years, computer simulation-based 3D virtual reality (VR) stereoscopic display technology has been used widely in a variety of domains, especially in the training field [1], [2], [3], [4], [5], [6], [7], [8]. Do et al. [9] considered that one of the advantages of 3D VR is to make an abstract concept concrete. Bhagat et al. [10] indicated that 3D VR training can motivate users to learn effectively. Aim et al. [11] conducted a systematic review to determine the effectiveness of 3D VR training in orthopedic surgery and indicated that 70% of their reviews showed 3D VR training led to a significant improvement in technical skills. Cates et al. [12] indicated that using 3D VR display technology in training can improve performance by 17–49%. Didehbani et al. [13] revealed that VR can improve the autism spectrum disorders students on social emotion recognition, social attribution, and executive function. Lin et al. [14] found that using integrated advanced display technology could help children with different disabilities to complete puzzle game tasks when compared to those use of traditional paper-based methods.

Most current stereoscope 3D displays can be classified into 2 categories: passive and active displays. Their display quality will affect the result of VR training. Youn et al. [15] investigated the impact of different 3D representation formats and different display technologies on perceptual 3D video quality. VR stereoscopic display technologies can generally be divided into two categories: eyeglasses and without glasses. Eyeglasses include passive polarization glasses (PPG), passive anaglyph glasses (PAG), active shutter glasses (ASG), and head-mounted displays (HMDs). Images produced on the eyes are split by the glasses worn, which allows users to enjoy a stereo effect. However, while users enjoy 3D images by wearing the appropriate glasses or HMD, such displays impose a great burden on users [16]. Besides, current HMDs provide a fixed lens focus, So et al. [17] suggested using a dynamically adjustable lens focus in HMDs to reduce the stereo fusion times. Misperception which is another issue commonly occurs on using stereoscopic displays. It involved the rotation of the viewers' head relative to the display [18] and the depth as well as the shape of virtual objects [19]. The light in the polarization direction opposite to that of the glass lens can be blocked using PPG with light-filtering properties, and the glass lens can pass the lights only in the same polarization direction. Therefore, the left and right eyes of users simultaneously receive light rays from glasses in the vertical or horizontal polarization direction respectively, thereby achieving stereoscopic visual imaging. PAG, which is also known as 3D glasses with red and blue lenses, is another common type of passive glasses. On the basis of the principle that only the light ray the same color as that of the glass lens can pass, PAG may provide users with a 3D visual experience by sending images of different colors to their eyes [20]. PAG is often used as a 3D imaging tool because of its simple imaging principle and affordable price. ASG is the most common active glass that allows the left and right eyes to receive different 60 Hz images by updating the monitor frequency to 120 Hz and bringing a 3D visual experience. It requires an improved frame rate and sync signal transmission instead of special construction to adjust color and polarization. ASG supports a multi-user view of stereo imaging and is widely used in the audiovisual entertainment industry [20].

Given that eyes are the major receptors in visual training, an excellent visual training interface must simultaneously consider operation performances and visual fatigue. Solari et al. [19] pointed out that the distortion of using VR/AR 3D display can cause visual fatigue. Other studies on visual fatigue mostly focused on display type (i.e., CRT, LED), character size, brightness, and color, but rarely considered the effects of different stereoscopic display technologies [21], [22], [23], [24]. Studies that considered the application of 3D VR stereoscopic display technologies in training likewise emphasized training performance but rarely discussed the effects of different stereoscopic display technologies on visual fatigue [25], [26], [27]. Therefore, the actual effects of different display technologies on visual fatigue and operational performance should be explored.

Visual fatigue measurement methods can be broadly divided into subjective rating questionnaire and objective measurement, which concerns the changes in the eye’s adaptability to external stimuli [28], [29], [30], [31], [32], [33], [34]. Measuring frequency change in the critical fusion frequency (CFF) of the participants is widely used to detect eye strain. For the same person, a high fatigue level corresponds to a low CFF. Moreover, the fatigue level can be determined by near-point accommodation (NPA). For the same person, the adjustment ability of the lens may be weakened in case of any eye fatigue, which reduces the refractive capability and increases NPA.

To investigate the effects of conventional 2D display and different 3D stereoscopic displays on the operation performances and visual fatigue of the participants, this study adopts different display technologies, including 2D display (2D display), anaglyph 3D stereo display (anaglyph 3D), and 3D shutter stereo display (3D shutter), for the disassembly/assembly of the self-developed motor and the hard disk. We postulated 4 hypotheses for current study: (1) Task complexity affects the operation performances. (2) Display technology affects the operation performances. (3) Use time affects visual fatigue. (4) Display technology affects visual fatigue.