Accommodative Vergence Research Articles

42.1: Invited Paper: Design Considerations for Near‐eye Displays using a Holographic Display Method

Introducing holographic display methods into near‐eye displays is currently a hot topic to solve vergence accommodation conflict. Due to the etendue conservation, it is hard to achieve a near‐eye display with both a large field of view and a large eye box. Design considerations have been discussed, and these information provide give inspiration to the following researches on both near‐eye displays and holographic devices.

A covered eye fails to follow an object moving in depth

To clearly view approaching objects, the eyes rotate inward (vergence), and the intraocular lenses focus (accommodation). Current ocular control models assume both eyes are driven by unitary vergence and unitary accommodation commands that causally interact. The models typically describe discrete gaze shifts to non-accommodative targets performed under laboratory conditions. We probe these unitary signals using a physical stimulus moving in depth on the midline while recording vergence and accommodation simultaneously from both eyes in normal observers. Using monocular viewing, retinal disparity is removed, leaving only monocular cues for interpreting the object’s motion in depth. The viewing eye always followed the target’s motion. However, the occluded eye did not follow the target, and surprisingly, rotated out of phase with it. In contrast, accommodation in both eyes was synchronized with the target under monocular viewing. The results challenge existing unitary vergence command theories, and causal accommodation-vergence linkage.

Enhancing Angular Resolution of Layered Light-Field Display by Using Monochrome Layers

A layered light-field display is composed of several liquid crystal layers located in front of a backlight. The light rays emitted from the backlight intersect with different pixels on the layers depending on the outgoing directions. Therefore, this display can show multi-view images (a light field) in accordance with the viewing direction. This type of displays can also be used for head-mounted displays (HMDs) thanks to its dense angular resolution. The angular resolution is an important factor, because sufficiently dense angular resolution can provide accommodation cues, preventing visual discomfort caused by vergence accommodation conflict. To further enhance the angular resolution of a layered display, we propose to replace some of the layers with monochrome layers. While keeping the pixel size unchanged, our method can achieve three times higher resolution than baseline architecture in the horizontal direction. To obtain a set of color and monochrome layer patterns for a target light field, we developed two computation methods based on non-negative tensor factorization and a convolutional neural network, respectively.

Approximated super multi-view head-mounted display to reduce visual fatigue.

To reduce the visual fatigue of the head-mounted displays, we propose an approximated super multi-view technique in which multiple viewpoints are generated two-dimensionally with an interval smaller than the pupil diameter using the time multiplexing technique, and left and right virtual images are two-dimensionally shifted in synchronization with the viewpoint generation. The proposed technique enlarges the depth of field of eyes to provide the accommodation-invariant feature so that the vergence-accommodation conflict is mitigated. We constructed an experimental system by using two LED arrays for the viewpoint generation and one LCD panel vibrated by two stepping motors. The proposed technique was then experimentally validated.

Compact vari-focal augmented reality display based on ultrathin, polarization-insensitive, and adaptive liquid crystal lens

Despite the recent advances in augmented reality (AR), which has shown the potential to significantly impact on our daily lives by offering a new way to manipulate and interact with virtual information, minimizing visual discomfort due to the vergence–accommodation conflict remains a challenge. Emerging AR technologies often exploit focus-tunable optics to address this problem. Although they demonstrated improved depth perception by enabling proper focus cues, a bulky form factor of focus–tunable optics prevents their use in the form of a pair of eyeglasses. Here, we propose a novel optical configuration for a compact vari-focal AR display which deliberately utilizes the zeroth and first diffraction orders of the LC lens to produce two foci: one for a real object and the other for a virtual object with addressable focal planes. The prototype AR glasses can adjust the accommodation distance of the virtual image, mitigating the vergence–accommodation conflict without substantially compromising the form factor or image quality. In addition, we describe the design, fabrication, and characterization of an ultrathin, polarization-insensitive focus-tunable liquid crystal (LC) diffractive lens with a large aperture, a low weight, and a low operating voltage. We show that the polarization dependence of the lens, which is an inherent optical property of LC lenses, can be insensitive using the trilayer birefringent materials and by aligning the optical axes of each birefringent material at a specific angle. The polarization insensitivity eliminates the need for a polarizer, thus further reducing the form factor of the optical system. This novel approach offers significantly reduced complexity for designing AR glasses with addressable focal planes. These technologies for ultrathin lens and AR display show promising potential for developing compact optical systems in various applications.

Depth Perception in Virtual Reality Systems: Effect of Screen Distance, Environment Richness and Display Factors

Viewing a scene on a screen display differs greatly from viewing it in the real world. The visual information is conveyed via a flat screen at a fixed distance, and this screen distance can influence how viewers perceive depth in stereograms in conventional stereoscopic displays. This study investigated whether screen distance influences perceived depth in Virtual Reality (VR) systems providing additional motion parallax information. Participants adjusted the depth of a vertical dihedron displayed as a random-dot stereogram. In a first experiment, the stimulus was presented either alone in a gray untextured background or in a cue-rich environment. We found that despite the extra motion parallax information in VR systems compared to conventional stereo-displays, physical screen distance still affected depth perception substantially at longer simulated distances. However, the effect lessened when observers were immersed in a rich and structured environment, possibly allowing them to use other depth cues. A second experiment assessed the influence of potentially potent display-related factors (resolution, display orientation, luminance non-uniformity, and specular reflection), as well as the effect of accommodation-vergence (A-V) conflict size. Depth perception was compared between a Head-Mounted Display (HMD) and an L-shaped system, and between a CAVE and an L-shaped system. These comparisons between CAVE-like VR systems and HMDs revealed that A-V conflict and inclusion of a rich environment were the major factors impacting depth perception. These results have practical and methodological implications for the reliable use of VR systems, especially where accurate depth-matching is involved.

Implementation and characterization of the optical-see-through Maxwellian near-eye display prototype using three-dimensional printing

By presenting always-in-focus virtual images, Maxwellian near-eye displays can remove the vergence accommodation conflict, which causes eye fatigue or dizziness. Described in this paper are an implementation process and observations of virtual images of the optical-see-through Maxwellian near-eye display prototype made with a three-dimensional printer.

3D Display System Based on Spherical Wave Field Synthesis

We present a novel concept and first experimental results of a new type of 3D display, which is based on the synthesis of spherical waves. The setup comprises a lens array (LA) with apertures in the millimeter range and a liquid crystal display (LCD) panel. Each pixel of the LCD creates a spherical wave cutout that propagates towards the observer. During the displaying process, the curvature of the spherical waves is dynamically changed by either changing the distance between LA and LCD or by adapting the focal lengths of the lenses. Since the system, similar to holography, seeks to approximate the wavefront of a natural scene, it provides true depth information to the observer and therefore avoids any vergence–accommodation conflict (VAC).

Subtitle Region Selection of S3D Images in Consideration of Visual Discomfort and Viewing Habit

Subtitles, serving as a linguistic approximation of the visual content, are an essential element in stereoscopic advertisement and the film industry. Due to the vergence accommodation conflict, the stereoscopic 3D (S3D) subtitle inevitably causes visual discomfort. To meet the viewing experience, the subtitle region should be carefully arranged. Unfortunately, very few works have been dedicated to this area. In this article, we propose a method for S3D subtitle region selection in consideration of visual discomfort and viewing habit. First, we divide the disparity map into multiple depth layers according to the disparity value. The preferential processed depth layer is determined by considering the disparity value of the foremost object. Second, the optimal region and coarse disparity value for S3D subtitle insertion are chosen by convolving the selective depth layer with the mean filter. Specifically, the viewing habit is considered during the region selection. Finally, after region selection, the disparity value of the subtitle is further modified by using the just noticeable depth difference (JNDD) model. Given that there is no public database reported for the evaluation of S3D subtitle insertion, we collect 120 S3D images as the test platform. Both objective and subjective experiments are conducted to evaluate the comfort degree of the inserted subtitle. Experimental results demonstrate that the proposed method can obtain promising performance in improving the viewing experience of the inserted subtitle.

AR Displays: Next-Generation Technologies to Solve the Vergence–Accommodation Conflict

Augmenting reality (AR) holds many benefits in how people perceive information and use it in their workflow or leisure activities. A cohesive AR experience has many components; nevertheless, the key is display technologies. The current industry standard for the core solution is still conventional stereoscopy, which has proven to be inadequate for near-work due to the caused vergence–accommodation conflict and the inability to precisely overlay the 3D content on the real world. To overcome this, next-generation technologies have been proposed. While the holographic method holds the highest potential of being the ultimate solution, its current level of maturity is not sufficient to yield a practical product. Consequently, the next solution for near-work-capable AR displays will be of another type. LightSpace Technologies have developed a static multifocal display architecture based on stacked liquid crystal-based optical diffuser elements and a synchronized high-refresh rate image projector. A stream of 2D image depth planes comprising a 3D scene is projected onto respective physically-separated diffuser elements, causing the viewer to perceive a scene as continuous and having all relevant physical as well as psychological depth cues. A system with six image depth planes yielding 6 cpd resolution and 72° horizontal field-of-view has been demonstrated to provide perceptually continuous accommodation over 3.2 Diopter range. A further optimization by using a conventional image combiner resulted in the compact and practical design of the AR display.

Discomfort of Visual Perception in Virtual and Mixed Reality Systems

The importance of the topic of this paper is caused by the rapid development of virtual, mixed, and augmented reality systems. A problem in designing virtual reality (VR), augmented reality (AR) and mixed reality (MR) systems is the assessment of the visual perception of the result, in particular, the assessment of discomfort caused either by differences in the illumination conditions of objects in the real and virtual worlds or by the conflict of the vergence and accommodation of vision of the device user. The standard optical characteristics, such as aberration, frequency and contrast characteristic, and others are not applicable to evaluating the discomfort of visual perception. On the other hand, the discomfort can be assessed using a real proptotype; however, its fabrication can be labor consuming and expensive. We propose methods for virtual prototyping of visual optical systems that can be used in designing AR, VR, and MR devices for the analysis of discomfort caused, for example, by the vergence–accommodation conflict in virtual and augmented reality systems or by differences in the illumination conditions of real and virtual scene objects in mixed reality systems.

3‐5: Late‐News Paper: Visual Fatigue Reducing 3D Glasses by Extending Depth of Field of Eyes

This work proposes three‐dimensional (3D) glasses, constructed from a combination of phase plates and conventional 3D glasses, which can extend the depth of field of eyes and reduce visual fatigue caused by the vergence–accommodation conflict. A subjective evaluation validated the effectiveness of the proposed technique.

73‐5: Late‐News Paper: Simplified Implementation of Super Multi‐View Head‐Mounted Display

Super multi‐view head‐mounted displays can solve the visual fatigue caused by the vergence–accommodation conflict. This study proposes their simplified implementation, which could greatly reduce the cost and computational load, by using a vibrated flat‐panel display illuminated by LEDs. The experimental validation is also reported.

The Effect of Vertically Yoked Prisms on Binocular Vision and Accommodation

Vertically yoked prisms have been used in treatment of binocular vision dysfunction despite minimal supporting evidence. In people with normal binocular vision, the impact on phorias has been assessed but not the impact on accommodation, accommodation vergence interactions, or the horopter. We found that vertically yoked prisms have minor effects during short-term wear in young adults. The purpose of this study was to determine effects of vertically yoked prisms on accommodative response and several binocular vision tasks. There were 45 participants aged 18 to 24 years. The 23 myopes wore distance-corrected soft contact lenses. In a random arrangement, each person wore spectacles containing planopower lenses with either 8 Δ base-up, 4 Δ base-up, zero, 4 Δ base-down, and 8 Δ base-down prisms. Before spectacle wear, baseline measurements of near heterophoria, accommodation response, negative and positive relative accommodations, fusional vergence, and Nonius-horopter spatial perception were taken. Measurements were repeated after a 40-minute wear, spectacles were removed, and tests were performed 20 minutes later. On a 22-participant subset, on a separate occasion, measurements of heterophoria, accommodation response, and relative accommodation were made immediately after spectacles were fitted. Most changes relative to baseline were not significant. Where effects occurred, these were nearly all associated with prism presence rather than adaptation. There were significant effects on accommodation response, but these seem to be refraction effects produced by pantoscopic tilt-induced power changes rather than perceptual effects altering accommodation. There were statistically significant effects on negative relative accommodation (P < .01), with zero prism giving more negative relative accommodation than 8 Δ base-down prisms. Tendencies were noted for prisms to move horopter limits toward the observer. Effects were small and likely not of clinical relevance. Vertically yoked prisms have minor effects on accommodation and binocular vision, at least during short-term wear in young adults with normal binocular vision.

Correlation Between the Type of Visual Function and Reading Ability by Tait-Wick and Duke-Elder Method

Purpose : The purpose of this study was to investigate the correlation between visual function and reading ability by Tait-Wick and Duke-Elder methods. Methods : In this study, 151 subjects without ocular disease and refractive error were classified by the Tait-Wick and Duke-Elder methods and their reading ability was examined. The visual function test was distance and near heterophoria, near point of convergence, amplitude of accommodation, distance and near fusional vergence, accommodative facility. The reading ability test was performed using ReadAlyzer to measure duration of fixation, numner of regression, reading rate, saccadic in return sweep, and comprehension. Results : Convergence insufficiency significantly decreased by duration of fixation(t=-2.423, p=0.019), significantly increased by numner of regression(t=4.770, p=0.000), and significantly decreased by reading rate than normal group(t=-5.674, p=0.000). In the accommodative facility, the numner of regression view increased and the reading rate decreased with a significant difference compared with the normal group. The other abnormal groups showed no significant correlation with the reading factor. Conclusion : As a result of this study, convergence insufficiency group seems that the reading rate is decreased because the duration of fixation is decreased and the numner of regression is increased because the convergence is not enough when reading. As the facility of accommodation decreased, increased the number of regression and decreased the reading rate. This suggests that even when the test distance is fixed at 40cm, a slight change in the accommodation stimulus occurs during reading and maladjustment has occurred. Some binocular dysfunction may affect the motional elements of reading, but they do not affect cognitive factors.

Induced vergence-accommodation conflict reduces cognitive performance in the Stroop test

Interaction mechanisms between cognition and binocular motor control in reading saccades remain unclear. In this study we examine objectively saccades and fixations parameters during the Stroop test, involving three different levels of cognitive demand (reading, color denomination and interference). In addition, we experimentally induce accommodation and vergence conflicts during the different tasks. Twenty-one visually normal subjects (age 20.9 ± 1.45) performed the Stroop test in three different randomized conditions: a control normal viewing condition, a 16Δ base-out prism condition, and a −2.50D spherical lenses condition. Prisms and spherical lenses induced Vergence-Accommodation conflict. Eye movements were recorded with the Eyeseecam video-oculography device. The results show (1) longer fixation duration in the interference task than in the denomination task, and shorter fixation duration in the reading task; (2) a higher interference effect in the conflict induced conditions compared to the control condition; (3) a lower tolerance to prism induced conflict, with a higher destabilization of the binocular motor control of saccades and fixations. This suggests an interplay between vergence accommodation conflict and cognitive load: tolerance to the conflict seems to be lower in the more cognitively demanding interference Stroop task. The results consolidate the link between cognition and high quality of single binocular vision.

Super multi-view near-eye display to solve vergence–accommodation conflict

A super multi-view (SMV) technique is applied to near-eye displays to solve the vergence-accommodation conflict that causes visual fatigue. The proposed SMV near-eye display employs a high-speed spatial light modulator (SLM), a two-dimensional (2D) light source array, and an imaging optics for each eye. The imaging optics produces a virtual image of the SLM and real images of the light sources to generate a 2D array of viewpoints. The SMV images are generated using a time-multiplexing technique: the multiple light sources sequentially emit light while the SLM synchronously displays corresponding parallax images. A monocular experimental system was constructed using a ferroelectric liquid crystal display and an LED array. A full-parallax SMV image generation with 21 viewpoints was demonstrated and a comparison of full-parallax and horizontal parallax SMV images provided.

Full‐color multi‐plane optical see‐through head‐mounted display for augmented reality applications

AbstractBased on fast‐response polymer‐stabilized liquid crystal scattering shutters, we designed a full‐color multi‐plane optical see‐through head‐mounted display for augmented reality applications. Red, green, and blue light‐emitting diodes (LEDs) are used to illuminate a digital micromirror device in time sequence to create a full‐color 3D scene. A quasi‐collimated image projection source, with a large depth of focus, was designed, in order to ensure sharp pictures projected on different polymer‐stabilized liquid crystal films at different depth. Our system provides high‐quality full‐color images with correct depth information and thus solves the accommodation–vergence conflict problem. A proof‐of‐concept binocular full‐color two‐plane optical see‐through head‐mounted display prototype is demonstrated.

증상이 있는 폭주부족 대학생에서 양안조절용이성과 이향운동용이성

증상이 있는 폭주부족 대학생에서 양안조절용이성과 이향운동용이성

Autostereoscopic three-dimensional displays based on electrowetting liquid lenses

Many consumers are interested in three-dimensional (3-D) technologies that make display images as real as possible. In response, a number of fairly mature 3-D technologies have already been introduced in various studies. Among them, we reviewed the integral imaging system and the multiview system, which can realize 3-D, from the past to the present. Those systems, however, suffer from problems such as depth range, two-dimensional (2-D) and 3-D conversions, and 3-D resolution. Therefore, a liquid lens is proposed as a technique to resolve the drawbacks. Using a liquid lens with variable focal length, the depth range was enhanced using a time-division multiplexing technique in an integral imaging system, and the function of 2-D and 3-D switching was enabled in a multiview system. Furthermore, methods were introduced to solve the problems of 3-D resolution reduction in multiview systems and vergence–accommodation conflicts in VR systems.