The zone of comfort: Predicting visual discomfort with stereo displays

Balance and coordination after viewing stereoscopic 3D television

Manufacturers and the media have raised the possibility that viewing stereoscopic 3D television (S3D TV) may cause temporary disruption to balance and visuomotor coordination. We looked for evidence of such effects in a laboratory-based study. Four hundred and thirty-three people aged 4-82 years old carried out tests of balance and coordination before and after viewing an 80 min movie in either conventional 2D or stereoscopic 3D, while wearing two triaxial accelerometers. Accelerometry produced little evidence of any change in body motion associated with S3D TV. We found no evidence that viewing the movie in S3D causes a detectable impairment in balance or in visuomotor coordination.

3D visual discomfort predictor: analysis of horizontal disparity and neural activity statistics

Being able to predict the degree of visual discomfort that is felt when viewing stereoscopic 3D (S3D) images is an important goal toward ameliorating causative factors, such as excessive horizontal disparity, misalignments or mismatches between the left and right views of stereo pairs, or conflicts between different depth cues. Ideally, such a model should account for such factors as capture and viewing geometries, the distribution of disparities, and the responses of visual neurons. When viewing modern 3D displays, visual discomfort is caused primarily by changes in binocular vergence while accommodation in held fixed at the viewing distance to a flat 3D screen. This results in unnatural mismatches between ocular fixations and ocular focus that does not occur in normal direct 3D viewing. This accommodation vergence conflict can cause adverse effects, such as headaches, fatigue, eye strain, and reduced visual ability. Binocular vision is ultimately realized by means of neural mechanisms that subserve the sensorimotor control of eye movements. Realizing that the neuronal responses are directly implicated in both the control and experience of 3D perception, we have developed a model-based neuronal and statistical framework called the 3D visual discomfort predictor (3D-VDP)that automatically predicts the level of visual discomfort that is experienced when viewing S3D images. 3D-VDP extracts two types of features: 1) coarse features derived from the statistics of binocular disparities and 2) fine features derived by estimating the neural activity associated with the processing of horizontal disparities. In particular, we deploy a model of horizontal disparity processing in the extrastriate middle temporal region of occipital lobe. We compare the performance of 3D-VDP with other recent discomfort prediction algorithms with respect to correlation against recorded subjective visual discomfort scores,and show that 3D-VDP is statistically superior to the other methods.

The rate of change of vergence-accommodation conflict affects visual discomfort

Stereoscopic (S3D) displays create conflicts between the distance to which the eyes must converge and the distance to which the eyes must accommodate. Such conflicts require the viewer to overcome the normal coupling between vergence and accommodation, and this effort appears to cause viewer discomfort. Vergence-accommodation coupling is driven by the phasic components of the underlying control systems, and those components respond to relatively fast changes in vergence and accommodative stimuli. Given the relationship between phasic changes and vergence-accommodation coupling, we examined how the rate of change in the vergence-accommodation conflict affects viewer discomfort. We used a stereoscopic display that allows independent manipulation of the stimuli to vergence and accommodation. We presented stimuli that simulate natural viewing (i.e., vergence and accommodative stimuli changed together) and stimuli that simulate S3D viewing (i.e., vergence stimulus changes but accommodative stimulus remains fixed). The changes occurred at 0.01, 0.05, or 0.25 Hz. The lowest rate is too slow to stimulate the phasic components while the highest rate is well within the phasic range. The results were consistent with our expectation: somewhat greater discomfort was experienced when stimulus distance changed rapidly, particularly in S3D viewing when the vergence stimulus changed but the accommodative stimulus did not. These results may help in the generation of guidelines for the creation and viewing of stereo content with acceptable viewer comfort.

Instability of the perceived world while watching 3D stereoscopic imagery: A likely source of motion sickness symptoms

Watching 3D content using a stereoscopic display may cause various discomforting symptoms, including eye strain, blurred vision, double vision, and motion sickness. Numerous studies have reported motion-sickness-like symptoms during stereoscopic viewing, but no causal linkage between specific aspects of the presentation and the induced discomfort has been explicitly proposed. Here, we describe several causes, in which stereoscopic capture, display, and viewing differ from natural viewing resulting in static and, importantly, dynamic distortions that conflict with the expected stability and rigidity of the real world. This analysis provides a basis for suggested changes to display systems that may alleviate the symptoms, and suggestions for future studies to determine the relative contribution of the various effects to the unpleasant symptoms.

Effect of mental fatigue caused by mobile 3D viewing on selective attention: an ERP study

This study investigated behavioral responses to and auditory event-related potential (ERP) correlates of mental fatigue caused by mobile three-dimensional (3D) viewing. Twenty-six participants (14 women) performed a selective attention task in which they were asked to respond to the sounds presented at the attended side while ignoring sounds at the ignored side before and after mobile 3D viewing. Considering different individual susceptibilities to 3D, participants' subjective fatigue data were used to categorize them into two groups: fatigued and unfatigued. The amplitudes of d-ERP components were defined as differences in amplitudes between time-locked brain oscillations of the attended and ignored sounds, and these values were used to calculate the degree to which spatial selective attention was impaired by 3D mental fatigue. The fatigued group showed significantly longer response times after mobile 3D viewing compared to before the viewing. However, response accuracy did not significantly change between the two conditions, implying that the participants used a behavioral strategy to cope with their performance accuracy decrement by increasing their response times. No significant differences were observed for the unfatigued group. Analysis of covariance revealed group differences with significant and trends toward significant decreases in the d-P200 and d-late positive potential (LPP) amplitudes at the occipital electrodes of the fatigued and unfatigued groups. Our findings indicate that mentally fatigued participants did not effectively block out distractors in their information processing mechanism, providing support for the hypothesis that 3D mental fatigue impairs spatial selective attention and is characterized by changes in d-P200 and d-LPP amplitudes.

Simulated disparity and peripheral blur interact during binocular fusion

We have developed a low-cost, practical gaze-contingent display in which natural images are presented to the observer with dioptric blur and stereoscopic disparity that are dependent on the three-dimensional structure of natural scenes. Our system simulates a distribution of retinal blur and depth similar to that experienced in real-world viewing conditions by emmetropic observers. We implemented the system using light-field photographs taken with a plenoptic camera which supports digital refocusing anywhere in the images. We coupled this capability with an eye-tracking system and stereoscopic rendering. With this display, we examine how the time course of binocular fusion depends on depth cues from blur and stereoscopic disparity in naturalistic images. Our results show that disparity and peripheral blur interact to modify eye-movement behavior and facilitate binocular fusion, and the greatest benefit was gained by observers who struggled most to achieve fusion. Even though plenoptic images do not replicate an individual’s aberrations, the results demonstrate that a naturalistic distribution of depth-dependent blur may improve 3-D virtual reality, and that interruptions of this pattern (e.g., with intraocular lenses) which flatten the distribution of retinal blur may adversely affect binocular fusion.

Examining 3-D Technologies in Laptop Displays

As 3-D content migrates to the laptop, it is important to understand if customers can perceive quality differences between the 3-D technologies and to know if they feel any discomfort with close-up viewing of 3-D displays. In this study, we compared the quality and viewing comfort of active, passive, and autostereoscopic (glasses-free) 3-D displays. We found that participants were able to discern differences in 3-D quality and comfort on laptop computer displays in realistic viewing conditions within a short period. Although the active and passive displays were comparable, the autostereoscopic display was rated lower in quality and viewing comfort.

Vergence facility with stereoscopic and nonstereoscopic targets

PURPOSE

To compare vergence facility with nonstereo and stereo targets in binocular symptomatic and asymptomatic subjects.

METHODS

Sixty-six students were divided into symptomatic and asymptomatic groups according to the Convergence Insufficiency Symptom Survey Questionnaire score. Vergence facility was tested at 40 cm by flipper prism 3Δ BI/12Δ BO (BI, base-in; BO, base-out). The targets used were a nonstereo target (a vertical column of small letter "E" of ~20/30 size), a stereo-local target (fifth set of circles of the Titmus test with stereoacuity of 100 arcsec), and a stereo-global target (page 6 of the TNO test with stereoacuity of 120 arcsec).

RESULTS

Repeated-measures analysis of variance showed differences in the mean vergence facility with different targets in all subjects and separately in two symptom groups (p < 0.001). In all subjects and separately in the symptomatic subjects, this difference was statistically significant among the three different targets (p < 0.05). In the asymptomatic subjects, this difference was not significant between the measured values with nonstereo and stereo-local targets (p > 0.05) but significant for the comparison of stereo-global targets with the other two targets. The receiver operating characteristic curve analysis showed the cutoff points 10.5, 10.5, and 9.75 cycles per minute with nonstereo, stereo-local, and stereo-global targets, respectively. The sensitivity of the three targets used was the same (97%). Specificity was 0.93 or higher with all three targets, with the highest specificity obtained with the stereo-global target (100%).

CONCLUSIONS

The highest vergence facility was obtained with a nonstereo target and the lowest was obtained with a stereo-global target. High sensitivity with all three targets means that there are few false-negative results with them, and the high specificity is indicative of low false-positive results. Hence, the vergence facility predictive value would be high in diagnosing binocular symptomatic patients using a 3Δ BI/12Δ BO prism flipper at near and a response cutoff of about 10 cycles per minute or less.

User experience while viewing stereoscopic 3D television

3D display technologies have been linked to visual discomfort and fatigue. In a lab-based study with a between-subjects design, 433 viewers aged from 4 to 82 years watched the same movie in either 2D or stereo 3D (S3D), and subjectively reported on a range of aspects of their viewing experience. Our results suggest that a minority of viewers, around 14%, experience adverse effects due to viewing S3D, mainly headache and eyestrain. A control experiment where participants viewed 2D content through 3D glasses suggests that around 8% may report adverse effects which are not due directly to viewing S3D, but instead are due to the glasses or to negative preconceptions about S3D (the 'nocebo effect'). Women were slightly more likely than men to report adverse effects with S3D. We could not detect any link between pre-existing eye conditions or low stereoacuity and the likelihood of experiencing adverse effects with S3D.

Effect of the accommodation-vergence conflict on vergence eye movements

With the broader use of stereoscopic displays, a flurry of research activity about the accommodation-vergence conflict has emerged to highlight the implications for the human visual system. In stereoscopic displays, the introduction of binocular disparities requires the eyes to make vergence movements. In this study, we examined vergence dynamics with regard to the conflict between the stimulus-to-accommodation and the stimulus-to-vergence. In a first experiment, we evaluated the immediate effect of the conflict on vergence responses by presenting stimuli with conflicting disparity and focus on a stereoscopic display (i.e. increasing the stereoscopic demand) or by presenting stimuli with matched disparity and focus using an arrangement of displays and a beam splitter (i.e. focus and disparity specifying the same locations). We found that the dynamics of vergence responses were slower overall in the first case due to the conflict between accommodation and vergence. In a second experiment, we examined the effect of a prolonged exposure to the accommodation-vergence conflict on vergence responses, in which participants judged whether an oscillating depth pattern was in front or behind the fixation plane. An increase in peak velocity was observed, thereby suggesting that the vergence system has adapted to the stereoscopic demand. A slight increase in vergence latency was also observed, thus indicating a small decline of vergence performance. These findings offer a better understanding and document how the vergence system behaves in stereoscopic displays. We describe what stimuli in stereo-movies might produce these oculomotor effects, and discuss potential applications perspectives.

Crosstalk reduction in stereoscopic 3D displays: disparity adjustment using crosstalk visibility index for crosstalk cancellation

Stereoscopic displays provide viewers with a truly fascinating viewing experience. However, current stereoscopic displays suffer from crosstalk that is detrimental to image quality, depth quality, and visual comfort. In order to reduce the perceived crosstalk in stereoscopic displays, this paper proposes a crosstalk reduction method that combines disparity adjustment and crosstalk cancellation. The main idea of the proposed method is to displace the visible crosstalk using the disparity adjustment in a way that less amounts of intensity leakage occur on perceptually important regions in a scene. To this purpose, we estimate a crosstalk visibility index map for the scene that represents pixel-by-pixel importance values associated with the amount of perceived crosstalk and negative-after-effects of the crosstalk cancellation. Based on the crosstalk visibility index, we introduce a new disparity adjustment method that reduces the annoying crosstalk in processed images, which is followed by the crosstalk cancellation. The effectiveness of the proposed method has been successfully evaluated by subjective assessments of image quality and viewing preference. Experimental results demonstrate that the proposed method effectively improves the image quality and overall viewing quality of stereoscopic videos.

Visual fatigue effects on vergence dynamics in asymptomatic individuals

PURPOSE

To evaluate objectively changes in vergence dynamics following intentional visual fatiguing tasks using congruent (C) and non-congruent (NC) vergence stimulus demands.

METHODS

Pre- and post-task vergence dynamics to a 10.3° disparity stimulus were recorded objectively in 12 adult, asymptomatic individuals for both convergence and divergence. There were two fatigue-inducing tasks: Congruent or C-task: Subjects altered bifixation (50 cycles) between reduced Snellen charts at 2 m and at 20 cm every 3 s. Non-congruent or NC task: Subjects performed 50 cycles of vergence flipper (7Δ BO/BI), while bifixating a reduced Snellen chart at 40 cm. Pre- and post-task mean amplitude, time constant, peak velocity, and steady-state response variability were compared.

RESULTS

There was a significant increase in mean post-task, steady-state response variability for both the C and NC tasks. However, there were no significant group differences for either convergence or divergence between the pre- and post-mean amplitude, time constant, and peak velocity parameters for both the C and NC tasks, although post-task peak velocity was consistently reduced.

CONCLUSIONS

Steady-state vergence response variability was found to be the critical objective parameter to demonstrate significant fatigue effects in the group. Peak velocity was also consistently reduced to a small extent in the NC task. We speculate that these fatigue effects are of a central, and not of peripheral, origin.

Multiview-video-plus-depth coding based on the advanced video coding standard

This paper presents a multiview-video-plus-depth coding scheme, which is compatible with the advanced video coding (H.264/AVC) standard and its multiview video coding (MVC) extension. This scheme introduces several encoding and in-loop coding tools for depth and texture video coding, such as depth-based texture motion vector prediction, depth-range-based weighted prediction, joint inter-view depth filtering, and gradual view refresh. The presented coding scheme is submitted to the 3D video coding (3DV) call for proposals (CfP) of the Moving Picture Experts Group standardization committee. When measured with commonly used objective metrics against the MVC anchor, the proposed scheme provides an average bitrate reduction of 26% and 35% for the 3DV CfP test scenarios with two and three views, respectively. The observed bitrate reduction is similar according to an analysis of the results obtained for the subjective tests on the 3DV CfP submissions.

Visual discomfort and depth-of-field

Visual discomfort has been reported for certain visual stimuli and under particular viewing conditions, such as stereoscopic viewing. In stereoscopic viewing, visual discomfort can be caused by a conflict between accommodation and convergence cues that may specify different distances in depth. Earlier research has shown that depth-of-field, which is the distance range in depth in the scene that is perceived to be sharp, influences both the perception of egocentric distance to the focal plane, and the distance range in depth between objects in the scene. Because depth-of-field may also be in conflict with convergence and the accommodative state of the eyes, we raised the question of whether depth-of-field affects discomfort when viewing stereoscopic photographs. The first experiment assessed whether discomfort increases when depth-of-field is in conflict with coherent accommodation-convergence cues to distance in depth. The second experiment assessed whether depth-of-field influences discomfort from a pre-existing accommodation-convergence conflict. Results showed no effect of depth-of-field on visual discomfort. These results suggest therefore that depth-of-field can be used as a cue to depth without inducing discomfort in the viewer, even when cue conflicts are large.

Insight into Vergence-Accommodation Mismatch

Prolonged use of conventional stereo displays causes viewer discomfort and fatigue because of the vergence-accommodation conflict. We used a novel volumetric display to examine how viewing distance, the sign of the vergence-accommodation conflict, and the temporal properties of the conflict affect discomfort and fatigue. In the first experiment, we presented a fixed conflict at short, medium, and long viewing distances. We compared subjects' symptoms in that condition and one in which there was no conflict. We observed more discomfort and fatigue with a given vergence-accommodation conflict at the longer distances. The second experiment compared symptoms when the conflict had one sign compared to when it had the opposite sign at short, medium, and long distances. We observed greater symptoms with uncrossed disparities at long distances and with crossed disparities at short distances. The third experiment compared symptoms when the conflict changed rapidly as opposed to slowly. We observed more serious symptoms when the conflict changed rapidly. These findings help define comfortable viewing conditions for stereo displays.

3D-holoscopic imaging: a new dimension to enhance imaging in minimally invasive therapy in urologic oncology

BACKGROUND AND PURPOSE

Existing imaging modalities of urologic pathology are limited by three-dimensional (3D) representation on a two-dimensional screen. We present 3D-holoscopic imaging as a novel method of representing Digital Imaging and Communications in Medicine data images taken from CT and MRI to produce 3D-holographic representations of anatomy without special eyewear in natural light. 3D-holoscopic technology produces images that are true optical models. This technology is based on physical principles with duplication of light fields. The 3D content is captured in real time with the content viewed by multiple viewers independently of their position, without 3D eyewear.

METHODS

We display 3D-holoscopic anatomy relevant to minimally invasive urologic surgery without the need for 3D eyewear.

RESULTS

The results have demonstrated that medical 3D-holoscopic content can be displayed on commercially available multiview auto-stereoscopic display.

CONCLUSION

The next step is validation studies comparing 3D-Holoscopic imaging with conventional imaging.

Are there side effects to watching 3D movies? A prospective crossover observational study on visually induced motion sickness

Background

The increasing popularity of commercial movies showing three dimensional (3D) images has raised concern about possible adverse side effects on viewers.

Methods and Findings

A prospective carryover observational study was designed to assess the effect of exposure (3D vs. 2D movie views) on self reported symptoms of visually induced motion sickness. The standardized Simulator Sickness Questionnaire (SSQ) was self administered on a convenience sample of 497 healthy adult volunteers before and after the vision of 2D and 3D movies. Viewers reporting some sickness (SSQ total score>15) were 54.8% of the total sample after the 3D movie compared to 14.1% of total sample after the 2D movie. Symptom intensity was 8.8 times higher than baseline after exposure to 3D movie (compared to the increase of 2 times the baseline after the 2D movie). Multivariate modeling of visually induced motion sickness as response variables pointed out the significant effects of exposure to 3D movie, history of car sickness and headache, after adjusting for gender, age, self reported anxiety level, attention to the movie and show time.

Conclusions

Seeing 3D movies can increase rating of symptoms of nausea, oculomotor and disorientation, especially in women with susceptible visual-vestibular system. Confirmatory studies which include examination of clinical signs on viewers are needed to pursue a conclusive evidence on the 3D vision effects on spectators.

Application of stereo-imaging technology to medical field

OBJECTIVES

There has been continuous development in the area of stereoscopic medical imaging devices, and many stereoscopic imaging devices have been realized and applied in the medical field. In this article, we review past and current trends pertaining to the application stereo-imaging technologies in the medical field.

METHODS

We describe the basic principles of stereo vision and visual issues related to it, including visual discomfort, binocular disparities, vergence-accommodation mismatch, and visual fatigue. We also present a brief history of medical applications of stereo-imaging techniques, examples of recently developed stereoscopic medical devices, and patent application trends as they pertain to stereo-imaging medical devices.

RESULTS

Three-dimensional (3D) stereo-imaging technology can provide more realistic depth perception to the viewer than conventional two-dimensional imaging technology. Therefore, it allows for a more accurate understanding and analysis of the morphology of an object. Based on these advantages, the significance of stereoscopic imaging in the medical field increases in accordance with the increase in the number of laparoscopic surgeries, and stereo-imaging technology plays a key role in the diagnoses of the detailed morphologies of small biological specimens.

CONCLUSIONS

The application of 3D stereo-imaging technology to the medical field will help improve surgical accuracy, reduce operation times, and enhance patient safety. Therefore, it is important to develop more enhanced stereoscopic medical devices.

Dynamic accommodative response to different visual stimuli (2D vs 3D) while watching television and while playing Nintendo 3DS console

PURPOSE

The aim of the present study was to compare the accommodative response to the same visual content presented in two dimensions (2D) and stereoscopically in three dimensions (3D) while participants were either watching a television (TV) or Nintendo 3DS console.

METHODS

Twenty-two university students, with a mean age of 20.3 ± 2.0 years (mean ± S.D.), were recruited to participate in the TV experiment and fifteen, with a mean age of 20.1 ± 1.5 years took part in the Nintendo 3DS console study. The accommodative response was measured using a Grand Seiko WAM 5500 autorefractor. In the TV experiment, three conditions were used initially: the film was viewed in 2D mode (TV2D without glasses), the same sequence was watched in 2D whilst shutter-glasses were worn (TV2D with glasses) and the sequence was viewed in 3D mode (TV3D). Measurements were taken for 5 min in each condition, and these sections were sub-divided into ten 30-s segments to examine changes within the film. In addition, the accommodative response to three points of different disparity of one 3D frame was assessed for 30 s. In the Nintendo experiment, two conditions were employed - 2D viewing and stereoscopic 3D viewing.

RESULTS

In the TV experiment no statistically significant differences were found between the accommodative response with TV2D without glasses (-0.38 ± 0.32D, mean ± S.D.) and TV3D (-0.37 ± 0.34D). Also, no differences were found between the various segments of the film, or between the accommodative response to different points of one frame (p > 0.05). A significant difference (p = 0.015) was found, however, between the TV2D with (-0.32 ± 0.32D) and without glasses (-0.38 ± 0.32D). In the Nintendo experiment the accommodative responses obtained in modes 2D (-2.57 ± 0.30D) and 3D (-2.49 ± 0.28D) were significantly different (paired t-test p = 0.03).

CONCLUSIONS

The need to use shutter-glasses may affect the accommodative response during the viewing of displays, and the accommodative response when playing Nintendo 3DS in 3D mode is lower than when it is viewed in 2D.

Stereoscopy and the Human Visual System

Stereoscopic displays have become important for many applications, including operation of remote devices, medical imaging, surgery, scientific visualization, and computer-assisted design. But the most significant and exciting development is the incorporation of stereo technology into entertainment: specifically, cinema, television, and video games. In these applications for stereo, three-dimensional (3D) imagery should create a faithful impression of the 3D structure of the scene being portrayed. In addition, the viewer should be comfortable and not leave the experience with eye fatigue or a headache. Finally, the presentation of the stereo images should not create temporal artifacts like flicker or motion judder. This paper reviews current research on stereo human vision and how it informs us about how best to create and present stereo 3D imagery. The paper is divided into four parts: (1) getting the geometry right, (2) depth cue interactions in stereo 3D media, (3) focusing and fixating on stereo images, and (4) how temporal presentation protocols affect flicker, motion artifacts, and depth distortion.

Visual Discomfort with Stereo 3D Displays when the Head is Not Upright

Properly constructed stereoscopic images are aligned vertically on the display screen, so on-screen binocular disparities are strictly horizontal. If the viewer's inter-ocular axis is also horizontal, he/she makes horizontal vergence eye movements to fuse the stereoscopic image. However, if the viewer's head is rolled to the side, the on-screen disparities now have horizontal and vertical components at the eyes. Thus, the viewer must make horizontal and vertical vergence movements to binocularly fuse the two images. Vertical vergence movements occur naturally, but they are usually quite small. Much larger movements are required when viewing stereoscopic images with the head rotated to the side. We asked whether the vertical vergence eye movements required to fuse stereoscopic images when the head is rolled cause visual discomfort. We also asked whether the ability to see stereoscopic depth is compromised with head roll. To answer these questions, we conducted behavioral experiments in which we simulated head roll by rotating the stereo display clockwise or counter-clockwise while the viewer's head remained upright relative to gravity. While viewing the stimulus, subjects performed a psychophysical task. Visual discomfort increased significantly with the amount of stimulus roll and with the magnitude of on-screen horizontal disparity. The ability to perceive stereoscopic depth also declined with increasing roll and on-screen disparity. The magnitude of both effects was proportional to the magnitude of the induced vertical disparity. We conclude that head roll is a significant cause of viewer discomfort and that it also adversely affects the perception of depth from stereoscopic displays.

Visual Discomfort and the Temporal Properties of the Vergence-Accommodation Conflict

The vergence-accommodation conflict associated with viewing stereoscopic 3D (S3D) content can cause visual discomfort. Previous studies of vergence and accommodation have shown that the coupling between the two responses is driven by a fast, phasic component. We investigated how the temporal properties of vergence-accommodation conflicts affect discomfort. Using a unique volumetric display, we manipulated the stimulus to vergence and the stimulus to accommodation independently. There were two experimental conditions: 1) natural viewing in which the stimulus to vergence was perfectly correlated with the stimulus to accommodation; and 2) conflict viewing in which the stimulus to vergence varied while the stimulus to accommodation remained constant (thereby mimicking S3D viewing). The stimulus to vergence (and accommodation in natural viewing) varied at one of three temporal frequencies in those conditions. The magnitude of the conflict was the same for all three frequencies. The young adult subjects reported more visual discomfort when vergence changes were faster, particularly in the conflict condition. Thus, the temporal properties of the vergence-accommodation conflict in S3D media affect visual discomfort. The results can help content creators minimize discomfort by making conflict changes sufficiently slow.

Wheatstone and the Origins of Moving Stereoscopic Images

The recent resurgence of stereoscopic films and television programmes occasions reflection on their origins. Experimental studies of stroboscopic (apparent) motion and stereoscopic vision have their origins in London in the decade from 1825 to 1835. Instruments were devised which simulated motion and depth: sequences of still images could appear to move, and paired pictures (with small horizontal disparities and presented to different eyes) were seen in depth. Until that time, the experience of motion was almost always a consequence of object or observer movement: apparent motion was a novelty. By contrast, stereoscopic vision was the near-universal experience of using two eyes in the natural environment, but its basis remained mysterious. The stereoscope rendered the normal conditions for seeing depth from disparity experimentally tractable. The instruments were called philosophical toys because they fulfilled the dual roles of furthering scientific experiment on the senses and of providing popular amusement. The investigations were initially driven by the need for stimulus control so that the methods of physics could be applied to the study of perceptual phenomena. Many varieties of stroboscopic discs and stereoscopes were devised thereafter and their popularity increased enormously after 1840, when combined with photography. Presenting sequences of stereoscopic photographs in apparent motion was attempted in the 1850s, but proved less successful. The catalyst involved in all these developments was Charles Wheatstone.

Creating effective focus cues in multi-plane 3D displays

Focus cues are incorrect in conventional stereoscopic displays. This causes a dissociation of vergence and accommodation, which leads to visual fatigue and perceptual distortions. Multi-plane displays can minimize these problems by creating nearly correct focus cues. But to create the appearance of continuous depth in a multi-plane display, one needs to use depth-weighted blending: i.e., distribute light intensity between adjacent planes. Akeley et al. [ACM Trans. Graph. 23, 804 (2004)] and Liu and Hua [Opt. Express 18, 11562 (2009)] described rather different rules for depth-weighted blending. We examined the effectiveness of those and other rules using a model of a typical human eye and biologically plausible metrics for image quality. We find that the linear blending rule proposed by Akeley and colleagues [ACM Trans. Graph. 23, 804 (2004)] is the best solution for natural stimuli.