Focus Cues Research Articles

Eccentricity effects on blur and depth perception.

Foveation and (de)focus are two important visual factors in designing near eye displays. Foveation can reduce computational load by lowering display details towards the visual periphery, while focal cues can reduce vergence-accommodation conflict thereby lessening visual discomfort in using near eye displays. We performed two psychophysical experiments to investigate the relationship between foveation and focus cues. The first study measured blur discrimination sensitivity as a function of visual eccentricity, where we found discrimination thresholds significantly lower than previously reported. The second study measured depth discrimination threshold where we found a clear dependency on visual eccentricity. We discuss the study results and suggest further investigation.

Multiplane displays based on liquid crystals for AR applications

AbstractMultiplane displays are capable of displaying 3D scenes with correct focus cues by creating multilayer 2D images in the display volume. Hence, such a 3D display technique could effectively address the accommodation‐vergence conflict (AVC) problem, which is prevalent in augmented reality (AR) displays. In this paper, we review the recent progress on multiplane AR displays based on liquid crystals (LCs) for AR applications. The working principle of multiplane AR displays is illustrated, the electro‐optical properties of the tunable LC devices are investigated and display prototypes are demonstrated. Finally, we discuss the prospects and challenges of multiplane AR displays based on LCs.

Personality-Based Engagement: An Examination of Personality and Message Factors on Consumer Responses to Social Media Advertisements

Social media advertising has seen a growth in media messages customized to appeal to highly specific characteristics of an identified target. However, the psychological determinants of consumer responses to such media content remain under-researched. An experiment was conducted to investigate the effect that consumer personality traits, regulatory focus, and product appeal have on consumers’ response to social media advertising messages. Alternate versions of the advertising stimulus were created to manipulate regulatory focus cues (promotion vs. prevention) and product appeal (hedonic vs. utilitarian). Four of the Big Five personality traits—extraversion, conscientiousness, openness, and neuroticism—were examined to detect differences in consumer responses. Significant main effects exist for all personality traits and interaction effects were found between a subset of the personality traits analyzed with regulatory focus and product appeal, thus lending evidence for the robustness of the Big-Five as a useful framework for assessing individual differences in an audience’s response to social media advertising and message persuasion.

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.

Neuromuscular Mechanisms Underlying Changes in Force Production during an Attentional Focus Task.

We examined the effects of attentional focus cues on maximal voluntary force output of the elbow flexors and the underlying physiological mechanisms. Eleven males participated in two randomized experimental sessions. In each session, four randomized blocks of three maximal voluntary contractions (MVC) were performed. The blocks consisted of two externally and two internally attentional focus cued blocks. In one of the sessions, corticospinal excitability (CSE) was measured. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax), respectively in the biceps brachii. Across both sessions forces were lower (p = 0.024) under the internal (282.4 ± 60.3 N) compared to the external condition (310.7 ± 11.3 N). Muscle co-activation was greater (p = 0.016) under the internal (26.3 ± 11.5%) compared with the external condition (21.5 ± 9.4%). There was no change in CSE. Across both sessions, force measurements were lower (p = 0.033) during the stimulation (279.0 ± 47.1 N) compared with the no-stimulation session (314.1 ± 57.5 N). In conclusion, external focus increased force, likely due to reduced co-activation. Stimulating the corticospinal pathway may confound attentional focus. The stimulations may distract participants from the cues and/or disrupt areas of the cortex responsible for attention and focus.

Systematic method for modeling and characterizing multilayer light field displays.

Conventional stereoscopic displays are subject to the well-known vergence-accommodation conflict (VAC) problem due to their lack of the ability to render correct focus cues of a 3D scene. A computational multilayer light field display has been explored as one of the approaches that can potentially overcome the VAC problem owing to the promise of rendering a true 3D scene by sampling the directions of the light rays apparently emitted by the 3D scene. Several pioneering works have demonstrated working prototypes of multilayer light field displays and the potential capability of rendering nearly correct focus cues. However, there is no systematic investigation upon methods for modeling and analyzing such a display, which is essential for further optimization and development of high-performance multilayer light field display systems. In this paper, we proposed a systemic analysis method for the multilayer light field displays by simulating the perceived retinal image which takes the display factors, the view-dependency of the reference light field, the diffraction effect, and the visual factors into consideration. Then we applied this model to investigate the accommodative response when observing the display engine.

Glasses-Free 3-D and Augmented Reality Display Advances: From Theory to Implementation

Four of the most viable glasses-free three-dimensional display methods were chosen for our research at NTU's Advanced Displays Laboratory. Our multilayer light field display enables a smaller form factor. Faster algorithms combined with horizontal parallax-only speed-up Tensor Display computation time. A spin-off from this is an augmented reality light field near-eye display with focus cues. Our head-tracked displays use a directional backlit liquid crystal display panel to produce multiple sets of exit pupil pairs that employ a head tracker to follow the users’ eyes. This enables a ‘plug and play solution’ where existing content can be used without resolution loss. We have developed three different spatio-temporally multiplexed super multiview display systems based on liquid crystal displays, organic light-emitting diodes and fast projectors. In this article, the background, status of the prototypes and their performance are explained, and the future direction of our research is described.

Spatial loss factor for the analysis of accommodation depth cue on near-eye light field displays

In order to address the vergence-accommodation conflict problem, a generalized model consisting of a human visual system for the 4D light field display system was proposed. This model includes the key factors, such as retinal resolution, the central depth plane (CDP), and the proposed spatial loss factor, for the light field display system. The spatial resolution of the target plane in the depth of field (DOF) were quantitatively evaluated based on the proposed model. The results showed that the inconsistency of spatial resolution in DOF results in unstable eye accommodation response. Based on the fovea resolution-limit, we evaluated and simulated the resolution of perceived images on retina and the accommodation response based on spatial loss factor. The simulation results verified that a near-eye light field display (NE-LFD) configuration with a spatial loss factor greater than 0.8, corresponding to 2 by 2 views, or a minimum spatial loss factor 0.6, corresponding to 3 by 3 views, has the ability to render a nearly correct focus cues and accommodation response.

Tomographic projector

Over the past century, as display evolved, people have demanded more realistic and immersive experiences in theaters. Here, we present a tomographic projector for a volumetric display system that accommodates large audiences while providing a uniform experience. The tomographic projector combines high-speed digital micromirror and three spatial light modulators to refresh projection images at 7200 Hz. With synchronization of the tomographic projector and wearable focus-tunable eyepieces, the presented system can reconstruct 60 focal planes for volumetric representation right in front of audiences. We demonstrate proof of concept of the proposed system by implementing a miniaturized theater environment. Experimentally, we show that this system has wide expressible depth range with focus cues from 25 cm to optical infinity with sufficient tolerance while preserving high resolution and contrast. We also confirm that the proposed system provides uniform experience in a wide range of viewing zone through simulation and experiment. Additionally, the tomographic projector has capability to equalize vergence state that varies in conventional stereoscopic 3D theater according to viewing position as well as interpupillary distance. This study is concluded with thorough discussion about tomographic projectors in terms of challenges and research issues.

Holographic multiplane near-eye display based on amplitude-only wavefront modulation.

We present a holographic multiplane near-eye display method based on Fresnel holography and amplitude-only wavefront modulation. Our method can create multiple focal images across a wide depth range while maintaining a high resolution (1080P) and refresh rate (60 Hz). To suppress the DC and conjugation signals inherent in amplitude-only wavefront modulation, we develop an optimization algorithm which completely separates primary diffracted light from DC and conjugation at a pre-defined intermediate plane. Spatial filtering at this plane leads to a dramatic increase in the image contrast. The experimental results demonstrate our approach can create continuous focus cues in complex 3D scenes.

Wavelength-multiplexed multi-focal-plane seethrough near-eye displays.

We demonstrate a multi-focal-plane see-through near-eye display with effective focus cues enabled by wavelength multiplexing. A spectral notch filter is implemented as the wavelength-sensitive depth separation element. The vergence-accommodation conflict can be mitigated with the proposed design without space- or time-multiplexing. Another design of a dual-focus projection module for the waveguide-type augmented reality devices using wavelength-multiplexing is also presented.

Generalized methods and strategies for modeling and optimizing the optics of 3D head-mounted light field displays.

An integral-imaging based light field head-mounted display, which typically renders a 3D scene by reconstructing the directional light rays apparently emitted by the scene via an array optics, is potentially capable of rendering correct or nearly correct focus cues and therefore solving the well-known vergence-accommodation conflict problem plaguing conventional stereoscopic displays. Its true 3D image formation nature, however, imposes significant complications and the well-established optical design process for conventional head-mounted displays becomes inadequate to address the design challenges. To our best knowledge, there are no existing methods or framework that have been previously proposed or demonstrated to address the challenges of modeling and optimizing an optical system for this type of display systems. In this paper, we present novel and generalizable methodology and framework for designing and optimizing the optical performance of integral-imaging based light field head-mounted displays, including methods of system configurations, user-defined metrics for characterizing the performance of such systems, and optimization strategies unique in light field displays. A design example is further given based on the proposed design methodology for the purpose of validating the proposed design method and framework.

The use of multiple externally directed attentional focus cues facilitates motor learning

Attentional focus research consistently suggests that the use of an external focus of attention improves motor learning and performance relative to an internal focus. It appears, however, that external focus cues are not frequently adopted in applied sport settings. One issue that may contribute to this disparity relates to variability in how cues are employed in research and practice. Experimental research tends to use a single-cue approach, while in sports, athletes often sample several cues within the same practice. A limitation of the single-cue approach is that attentional focus effects could be due either to focus direction (internal vs. external) or to the relative effectiveness of a particular cue (e.g. an effective externally focused cue vs. an ineffective internally focused cue). This study tested whether external focus benefits generalize to situations in which participants use multiple cues of the same type throughout acquisition. Volunteers ( N = 22) learned a dart throwing task while using three internally or externally focused cues. Results indicated an external focus led to lower error scores during acquisition and a delayed retention test ( p’s < .05). These results demonstrate that the external focus benefit generalizes to situations where a performer uses multiple cues.

Considering a Holistic Focus of Attention as an Alternative to an External Focus

Empirical findings consistently suggest that an external focus of attention leads to superior performance when compared to an internal focus by encouraging more automatic processing. However, for certain skills (e.g., gymnastics routines) it can be challenging to identify a meaningful external focus cue. A related line of research suggests that focusing on the general feeling of a movement (i.e., holistic focus) may also be useful in avoiding conscious control of movements. The purpose of this study was to determine how an internal focus (INT), external focus (EXT), and holistic focus (HOL) impact the performance of a standing long jump. Participants (N = 27) completed two baseline jumps followed by two jumps in each focus condition. Jump distance was analyzed in a 6 (Order) × 4 (Focus) mixed ANOVA. Results indicated a significant main effect of focus (p < .001), with EXT and HOL resulting in farther jumps than INT and baseline conditions (p-values < .05). EXT and HOL did not differ significantly from each other, and INT did not differ significantly from baseline. The findings suggest that a holistic focus can be another effective means of avoiding conscious control of movement when an external focus is not practical or desired.

Stimulation Techniques used to Assess Corticospinal Excitability Alters an Attentional Focus Maximal Voluntary Contraction of the Elbow Flexors.

PURPOSE: To investigate the role of attentional focus on force output by assessing 1) force output during maximal voluntary elbow flexion contractions, 2) corticospinal excitability and 3) motor unit activation patterns METHODS: 7 resistance-trained males completed two experimental sessions. Each session consisted of 12 maximum voluntary contractions (MVC) with 180s rest of recovery between MVC. Participants were given counter-balanced external and internal attentional focus conditions prior to each MVC to direct attention. Force output and electromyography (EMG) of the biceps brachii, triceps brachii, and brachioradialis were recorded for both sessions. Transcranial magnetic stimulation, transmastoid electrical stimulation, and brachial plexus electrical stimulation were used to produce motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs) and maximal M-waves (Mmax) in the biceps brachii during each MVC in one of the two sessions. All MEPs and CMEPs were normalized to Mmax. RESULTS: Forces produced during the stimulation session were not significantly different between external and internal focus conditions (p = 0.20). However, forces produced during the non-stimulation session were 19.9% higher with an external cue compared to internal cues (p < 0.05). As well, forces produced with external cues were 13.2% greater during the non-stimulation session compared to the stimulation session. (p<0.05). EMG activity was not found to be significantly different between attention focus cues (p≥0.1). CONCLUSIONS: The usage of stimulation techniques likely distracted participants from the attentional focus cues provided during the stimulation session. Therefore, we were unable to successfully assess changes in corticospinal excitability between focus cues. However, we were still able to show that external cues direct greater force production of the elbow flexors compared to internal cues.

Design and demonstration of a vari-focal optical see-through head-mounted display using freeform Alvarez lenses.

Alvarez lenses offer accurate and high-speed, dynamic tuning of optical power through a lateral shifting of two lens elements, making them an appealing solution to eliminate the inherent decoupling of accommodation and convergence seen in conventional stereoscopic displays. In this paper, we present a design of a compact eyepiece coupled with two lateral-shifting freeform Alvarez lenses to enable a compact, high-resolution, optical see-through head-mounted display (HMD). The proposed design is able to tune its focal depth from 0 to 3 diopters, rendering near-accurate focus cues with high image quality and a large undistorted see-through field of view (FOV). Our design utilizes an 1920x1080 color resolution organic light-emitting diode (OLED) microdisplay to achieve a >30 degree virtual diagonal FOV, with an angular resolution of <0.85 arcminutes and an average optical performance of > 0.4 contrast over the full field. We also experimentally demonstrate a fully functional benchtop prototype using mostly off-the-shelf optics.

Perceptual Limits of Optical See-Through Visors for Augmented Reality Guidance of Manual Tasks

The focal length of available optical see-through (OST) head-mounted displays (HMDs) is at least 2m; therefore, during manual tasks, the user eye cannot keep in focus both the virtual and real content at the same time. Another perceptual limitation is related to the vergence-accommodation conflict, the latter being present in binocular vision only. This paper investigates the effect of incorrect focus cues on the user performance, visual comfort, and workload during the execution of augmented reality (AR)-guided manual task with one of the most advanced OST HMD, the Microsoft HoloLens. An experimental study was designed to investigate the performance of 20 subjects in a connect-the-dots task, with and without the use of AR. The following tests were planned: AR-guided monocular and binocular, and naked-eye monocular and binocular. Each trial was analyzed to evaluate the accuracy in connecting dots. NASA Task Load Index and Likert questionnaires were used to assess the workload and the visual comfort. No statistically significant differences were found in the workload, and in the perceived comfort between the AR-guided binocular and monocular test. User performances were significantly better during the naked eye tests. No statistically significant differences in performances were found in the monocular and binocular tests. The maximum error in AR tests was 5.9mm. Even if there is a growing interest in using commercial OST HMD, for guiding high-precision manual tasks, attention should be paid to the limitations of the available technology not designed for the peripersonal space.

Dual focal plane augmented reality interactive display with gaze-tracker

Stereoscopic augmented reality (AR) displays have a fixed focus plane and they suffer from visual discomfort due to vergence-accommodation conflict (VAC). In this study, we demonstrated a biocular (i.e. common optics for two eyes and same images are shown to both eyes) two focal-plane based AR system with real-time gaze tracker, which provides a novel interactive experience. To mitigate VAC, we propose a see-through near-eye display mechanism that generates two separate virtual image planes at arm’s length depth levels (i.e. 25 cm and 50 cm). Our optical system generates virtual images by relaying two liquid crystal displays (LCDs) through a beam splitter and a Fresnel lens. While the system is limited to two depths and discontinuity occurs in the virtual scene, it provides correct focus cues and natural blur effect at the corresponding depths. This allows the user to distinguish virtual information through the accommodative response of the eye, even when the virtual objects overlap and partially occlude in the axial direction. The system also provides correct motion parallax cues within the movement range of the user without any need for sophisticated head trackers. A road scene simulation is realized as a convenient use-case of the proposed display so that a large monitor is used to create a background scene and the rendered content in the LCDs is augmented into the background. Field-of-view (FOV) is 60 × 36 degrees and the eye-box is larger than 100 mm, which is comfortable enough for two-eye viewing. The system includes a single camera-based pupil and gaze tracker, which is able to select the correct depth plane based on the shift in the interpupillary distance with user’s convergence angle. The rendered content can be distributed to both depth planes and the background scene simultaneously. Thus, the user can select and interact with the content at the correct depth in a natural and comfortable way. The prototype system can be used in tasks that demand wide FOV and multiple focal planes and as an AR and vision research tool.

The effects of instructional cues on performance and mechanics during a gross motor movement

Externally focused instructions specific to performance have shown to improve body mechanics (Gokeler et al., 2015; Welling, Benjaminse, Gokeler, & Otten, 2016). However, the effect of using an external focus instruction may have been more profound if the content of the instruction had been relevant to mechanics. Therefore, the present study examined the effects of externally focused instructions specific to performance and externally focused instructions specific to body mechanics on mechanics and performance. Twenty-four adults (n = 12 males; n = 12 females) performed a series of drop jumps following external focus cues that were specific to performance and landing mechanics. Participants completed a drop jump followed by a maximal effort vertical jump. The initial contact, maximal angle, and range of motion at the knee in the sagittal and frontal plane motion were measured for mechanics and the height of the second vertical jump was measured for performance. The results suggest external focus instructions specific to performance are beneficial for performance, but not for improving landing mechanics. This suggests that external focus instructions must be specific to the contents of the instruction.

All-passive transformable optical mapping near-eye display

We present an all-passive, transformable optical mapping (ATOM) near-eye display based on the “human-centric design” principle. By employing a diffractive optical element, a distorted grating, the ATOM display can project different portions of a two-dimensional display screen to various depths, rendering a real three-dimensional image with correct focus cues. Thanks to its all-passive optical mapping architecture, the ATOM display features a reduced form factor and low power consumption. Moreover, the system can readily switch between a real-three-dimensional and a high-resolution two-dimensional display mode, providing task-tailored viewing experience for a variety of VR/AR applications.