The Impact of Dynamic Convergence on the Human Visual System in Head Mounted Displays

<p>The Accommodation-Vergence Conflict (AVC) is a phenomenon in the area of Head-Mounted Displays (HMDs) and one of the key issues hindering the popularity of HMDs largely due to it causing a large number of users to suffer from simulator sickness. There have been several proposed solutions developed by previous researchers, including the introduction of 'Dynamic Convergence' (DC) which, addresses the AVC problem in terms of the vergence depth cue. DC also helps in the performance of binocular fusion when viewing at a close vergence depth. As of yet however, DC has not undergone detailed testing for a number of important cases, which limits the amount of data that has been collected on DC's interaction with the human visual system. In addition, no DC research as of yet has dealt with the effect of a change in vergence depth, and how that change in the vergence angle of the focal plane would effect a user. Thus, this thesis adds to the growing body of research and knowledge in this field by implementing DC with the addition of some transitions between a change in vergence depth. This is done within the Unity3D game engine in order to further investigate the impact of DC with regard to viewing close virtual objects on HMDs through a number of cases. The added transitions are also tested to see if they have any beneficial effects for users when the vergence angle changes. The investigation is centered around a perception based performance/appreciation-oriented visual study whereby participants were asked about their ability to perform binocular fusion on close virtual objects that were either stationary or moving and varying distances and speeds. Participants were also asked to report any symptoms of discomfort. The research has adopted a mixed methodology experimental approach by conducting user experiments and surveys, before analysing the results through both in-depth quantitative statistical analysis and a variety of qualitative statistical techniques in order to measure and investigate the scale of the problem associated with the impact of DC on the human visual system in HMDs when viewing close virtual objects. From the investigation it was confirmed that the approximate effective vergence depth range for DC was 0.3m or less, with statistical significance confirmed at the 0.15m distance. Participants reported having an easier time performing binocular fusion at these closer distances while DC was enabled. As a result of this, the majority of cases and scenarios did not report any significant negative responses in terms of discomfort symptoms. However attempts at improving DC with a transition between vergence depths were met with a mixed response from participants. While the need of a transition way be dependent on the user, there still exists some demand for one, thus it should still be available as an option.</p>

The Impact of Dynamic Convergence on the Human Visual System in Head Mounted Displays

<p>The Accommodation-Vergence Conflict (AVC) is a phenomenon in the area of Head-Mounted Displays (HMDs) and one of the key issues hindering the popularity of HMDs largely due to it causing a large number of users to suffer from simulator sickness. There have been several proposed solutions developed by previous researchers, including the introduction of 'Dynamic Convergence' (DC) which, addresses the AVC problem in terms of the vergence depth cue. DC also helps in the performance of binocular fusion when viewing at a close vergence depth. As of yet however, DC has not undergone detailed testing for a number of important cases, which limits the amount of data that has been collected on DC's interaction with the human visual system. In addition, no DC research as of yet has dealt with the effect of a change in vergence depth, and how that change in the vergence angle of the focal plane would effect a user. Thus, this thesis adds to the growing body of research and knowledge in this field by implementing DC with the addition of some transitions between a change in vergence depth. This is done within the Unity3D game engine in order to further investigate the impact of DC with regard to viewing close virtual objects on HMDs through a number of cases. The added transitions are also tested to see if they have any beneficial effects for users when the vergence angle changes. The investigation is centered around a perception based performance/appreciation-oriented visual study whereby participants were asked about their ability to perform binocular fusion on close virtual objects that were either stationary or moving and varying distances and speeds. Participants were also asked to report any symptoms of discomfort. The research has adopted a mixed methodology experimental approach by conducting user experiments and surveys, before analysing the results through both in-depth quantitative statistical analysis and a variety of qualitative statistical techniques in order to measure and investigate the scale of the problem associated with the impact of DC on the human visual system in HMDs when viewing close virtual objects. From the investigation it was confirmed that the approximate effective vergence depth range for DC was 0.3m or less, with statistical significance confirmed at the 0.15m distance. Participants reported having an easier time performing binocular fusion at these closer distances while DC was enabled. As a result of this, the majority of cases and scenarios did not report any significant negative responses in terms of discomfort symptoms. However attempts at improving DC with a transition between vergence depths were met with a mixed response from participants. While the need of a transition way be dependent on the user, there still exists some demand for one, thus it should still be available as an option.</p>

Interocular conflict from a monocular augmented reality display: Impact of visual characteristics on performance

In monocular see-through augmented reality systems, each eye is stimulated differently by a monocular image that is superimposed on the binocular background. This can impair binocular fusion, due to interocular conflict. As a function of visual characteristics, the latter can have a greater or lesser impact on user comfort and performance. This study tested several visual characteristics of a binocular background and a monocular element during an exposure that reproduced the interocular conflict induced by a monocular see-through near-eye display. The aim was to identify which factors impact the user’s performance. Performance was measured as target tracking and event detection, identification, fixation time, and latency. Our results demonstrate that performance is a function of the binocular background. Furthermore, exogenous attentional stimulation, in the form of a pulse with different levels of contrast applied to the monocular display, appears to preserve performance in most background conditions.

Binocular fusion enhances the efficiency of spot-the-difference gameplay

Spot-the-difference, the popular childhood game and a prototypical change blindness task, involves identification of differences in local features of two otherwise identical scenes using an eye scanning and matching strategy. Through binocular fusion of the companion scenes, the game becomes a visual search task, wherein players can simply scan the cyclopean percept for local features that may distinctly stand-out due to binocular rivalry/lustre. Here, we had a total of 100 visually normal adult (18–28 years of age) volunteers play this game in the traditional non-fusion mode and after cross-fusion of the companion images using a hand-held mirror stereoscope. The results demonstrate that the fusion mode significantly speeds up gameplay and reduces errors, relative to the non-fusion mode, for a range of target sizes, contrasts, and chromaticity tested (all, p<0.001). Amongst the three types of local feature differences available in these images (polarity difference, presence/absence of a local feature difference and shape difference in a local feature difference), features containing polarity difference was identified as first in ~60–70% of instances in both modes of gameplay (p<0.01), with this proportion being larger in the fusion than in the non-fusion mode. The binocular fusion advantage is lost when the lustre cue is purposefully weakened through alterations in target luminance polarity. The spot-the-difference game may thus be cheated using binocular fusion and the differences readily identified through a vivid experience of binocular rivalry/lustre.

How We See the World in Depth

This chapter explains how 3D vision and figure-ground perception occur in our brains. It shows how the 2D boundary and surface processes that are described in earlier chapters naturally generalize to 3D via both the FACADE (Form-And-Color-And-DEpth) theory of 3D vision and figure-ground perception, and the 3D LAMINART model that generalizes the laminar cortical circuits of Chapter 10 to 3D and naturally embodies and generalizes FACADE. Contrast-specific binocular fusion and contrast-invariant boundary formation are explained in terms of identified cells in specific layers of cortical areas V1 and V2. The correspondence problem is solved using a disparity filter that eliminates false binocular matches in layer 2/3 of V2, while it chooses the 3D binocular boundary grouping that is best supported by scenic cues. The critical role of monocular boundary information in figure-ground perception is explained and used to simulate DaVinci stereopsis percepts, along with surface-to-boundary surface contour signals and a fixation plane bias due to life-long experiences with fixated scenic features. Simulated data include the Venetian blind effect, Panum’s limiting case, dichoptic masking, 3D Craik-O’Brien-Cornsweet effect, Julesz random dot stereograms, 3D percepts of 2D pictures of shaded ellipses and discrete textures, simultaneous fusion and rivalry percepts when viewing Kulikowski and Kaufman stereograms, stimulus rivalry and eye rivalry, and bistable percepts of slanted surfaces, including the Necker cube. The size-disparity correlation enables signals from multiple scales to cooperate and compete to generate boundary representations at multiple depths. 3D percepts of natural scenes from stereograms are also simulated with these circuits.

Small temporal asynchronies between the two eyes in binocular reading: Crosslinguistic data and the implications for ocular prevalence

We investigated small temporal nonalignments between the two eyes’ fixations in the reading of English and Chinese. We define nine different patterns of asynchrony and report their spatial distribution across the screen of text. We interpret them in terms of their implications for ocular prevalence—prioritizing the input from one eye over the input from the other eye in higher perception/cognition, even when binocular fusion has occurred. The data are strikingly similar across the two very different orthographies. Asynchronies, in which one eye begins the fixation earlier and/or ends it later, occur most frequently in the hemifield corresponding to that eye. We propose that such small asynchronies cue higher processing to prioritize the input from that eye, during and after binocular fusion.

Alternative Flicker Glass: a New Anti-suppression Approach to the Treatment of Anisometropic Amblyopia

Introduction: Amlyopia always presents with monocular and binocular dysfunction. In this study, we aim to investage the efficacy of alternative occlusion using liquid crystal glasses versus continuous occlusion therapy using traditional patches for treating amblyopia. Methods: Eligible subjects with anisometropic amblyopia were randomized into two groups: alternative flicker glass (AFG) or patching group. In the AFG group, subjects were instructed to wear the flicker glasses for 1 hour a day. The AFG is a lightweight spectacle frame with liquid crystal lenses that provide direct square-wave alternating occlusion, which were pre-programmed at temporal frequency of 7Hz. In the patching group, the patients were prescribed to wear traditional patches for 2 hours a day. The best corrected visual acuity (BCVA), contrast sensitivity function (CSF) and stereoacuity were measured at the baseline, 3 and 12 weeks. Results: In this pilot study, a total of forty children were recruited, with twenty in the AFG group. Mean BCVA improved by 0.17±0.14logMAR (95% CI=0.10 to 0.23) in the AFG group, while 0.18±0.18logMAR (95% CI=0.09 to 0.26) in the patching group from baseline to 12 weeks. The improvement of BCVA in both groups were significant (both P＜0.01), while no significant difference between the groups (P=0.82). The CSF of both low and high spatial frequencies exhibited significant improvement at 12 weeks in the AFG group (P＜0.01, respectively), while just have a significant improvement at low spatial frequency in the patching group (P＜0.01). The stereoacuity significantly improved by 504.00±848.00 (95% CI= -900.88 to -107.12) arc seconds in the AFG group (P＜0.05), while 263.50± 639.55 (95% CI=-562.82 to 35.82) arc seconds in the patching group (P＞0.05). Conclusion: Alternative flicker glass was effective in improving both monocular and binocular function, which was most likely achieved by reducing the suppression and promoting binocular fusion. This therapy exhibited promise as an alternative method for amblyopia treatment.