Vergence Research Articles

Vergence eye movements in virtual reality

There is increasing interest in incorporating eye tracking in virtual reality (VR) systems to infer gaze in 3 dimensions. Estimation of gaze in depth may be limited by errors of measurement of the small eye vergence angles involved. It may also be limited by true errors of vergence in VR. We found that observers commonly made errors of vergence when viewing in VR, such that the dominant eye was more accurately aligned than the non-dominant eye. Errors of vergence were often larger than Panum’s fusional range. The absence of reported diplopia suggests that some of the visual input from one eye was supressed or the double images escaped attention. Errors of vergence could not be explained by contamination by variations in pupil diameter. Errors of vergence were not reduced when the vergence-accommodation conflict was eliminated by optical correction. These results suggest that the ability to correctly infer gaze distance in VR may be limited by true errors of eye vergence, rather than by measurement errors imposed by limitations of eye tracking.

Effects of Eye Vergence and Accommodation on Interactions with Content on an AR Magic-lens Display and its Surroundings.

Augmented reality (AR) magic-lens (ML) displays, such as handheld devices, offer a convenient and accessible way to enrich our environment using virtual imagery. Several display technologies, including conventional monocular, less common stereoscopic, and varifocal displays, are currently being used. Vergence and accommodation effects on depth perception, as well as vergence-accommodation conflict, have been studied, where users interact only with the content on the display. However, little research exists on how vergence and accommodation influence user performance and cognitive-task load when users interact with the content on a display and its surroundings in a short timeframe. Examples of this are validating augmented instructions before making an incision andperforming general hand-eye coordinated tasks such as grasping augmented objects. To improve interactions with future AR displays in such scenarios, we must improve our understanding of this influence. To this end, we conducted two fundamental visual-acuity user studies with 28 and 27 participants, while investigating eye vergence and accommodation distances on four ML displays. Our findings show that minimizing the accommodation difference between the display and its surroundings is crucial when the gaze between the display and its surroundings shifts rapidly. Minimizing the difference in vergence is more important when viewing the display and its surroundings as a single context without shifting the gaze. Interestingly, the vergence-accommodation conflict did not significantly affect the cognitive-task load nor play a pivotal role in the accuracy of interactions with AR ML content and its physical surroundings.

Comparison of Eye-Tracking Parameters and Brain Oxygen Saturation in Patients with COVID-19 Moderate Pneumonia.

A single-centre, non-randomised study included 92 patients in the acute period of SARS-CoV-2 moderate pneumonia (Delta variant). The mean time from admission was 1.5±0.9days. M:49, W:43. The mean age was 34.7±3.9years. The eye vergence reactivity index (VRx) was determined using a mobile ET. The cerebral oximetry was performed using Fore-Sight 2030 and included the detection of the SctO2 level in the frontal lobe (FLP) region. Statistical analysis was carried out using the methods of parametric statistics. The calculated vertical VRx was 0.781±0.118. The calculated horizontal VRx was 0.821±0.107. SctO2 in the FLP varied within the range from 61% to 73%. The average SctO2 values were 65.4±5.2% over the left FLP and 66.2±6.3% over the right FLP (p=0.872). The regression analysis showed that HVRx and VVRx were correlated with SctO2 levels in both FLPs (p=0.035 and p=0.034, respectively, and p=0.040 and p=0.049, respectively). Cerebral oxygen saturation in moderate pneumonia caused by the SARS-CoV-2 coronavirus has a significant destabilising effect on the oculomotor synergy (VVRx and HVRx) (p<0.05).

Broadening of attention dilates the pupil

Inconclusive evidence suggests that the pupil is more dilated when the breadth of attention is broad compared to narrow. To further investigate this relationship, we recorded pupil size from healthy volunteers while inducing trial-wise changes in breadth of attention using a shape-discrimination task where participants had to remember the location of a gap in a small or a large circle. A visual search task with targets presented at different distances from the centre of the screen was used to behaviourally assess the success of the manipulation of breadth of attention. Data were analysed using a generalised additive mixed model to test the experimental effects on pupil size after controlling for the effects of gaze location and eye vergence. The results showed that the pupil was more dilated in the broad-breadth-of-attention condition compared to the narrow-breadth-of-attention condition. However, the effect of attentional breadth on visual search performance was not mediated by pupil size, suggesting that more research is needed to understand the functional role of pupil dilation in relation to breadth of attention.

Why and when do you look away when trying to remember? Gaze aversion as a marker of the attentional switch to the internal world during memory retrieval

It is common to look away while trying to remember specific information, for example during autobiographical memory retrieval, a behavior referred to as gaze aversion. Given the competition between internal and external attention, gaze aversion is assumed to play a role in visual decoupling, i.e., suppressing environmental distractors during internal tasks. This suggests a link between gaze aversion and the attentional switch from the outside world to a temporary internal mental space that takes place during the initial stage of memory retrieval, but this assumption has never been verified so far. We designed a protocol where 33 participants answered 48 autobiographical questions while their eye movements were recorded with an eye-tracker and a camcorder. Results indicated that gaze aversion occurred early (median 1.09 s) and predominantly during the access phase of memory retrieval—i.e., the moment when the attentional switch is assumed to take place. In addition, gaze aversion lasted a relatively long time (on average 6 s), and was notably decoupled from concurrent head movements. These results support a role of gaze aversion in perceptual decoupling. Gaze aversion was also related to higher retrieval effort and was rare during memories which came spontaneously to mind. This suggests that gaze aversion might be required only when cognitive effort is required to switch the attention toward the internal world to help retrieving hard-to-access memories. Compared to eye vergence, another visual decoupling strategy, the association with the attentional switch seemed specific to gaze aversion. Our results provide for the first time several arguments supporting the hypothesis that gaze aversion is related to the attentional switch from the outside world to memory.

When is a disparity not a disparity? Toward an old theory of three-dimensional vision.

The aims of this paper are twofold: first, to discuss and analyze the concept of binocular disparity and second, to contrast the traditional "air theory" of three-dimensional vision with the much older "ground theory," first suggested by Ibn al-Haytham more than a thousand years ago. The origins of an "air theory" of perception can be traced back to Descartes and subsequently to the philosopher George Berkeley, who claimed that distance "could not be seen" because points lying along the same line of sight (in an empty space) would all project to the same location on the retina. However, Descartes was also aware that the angle of convergence of the two eyes could solve the problem of the "missing" information for the monocular observer and, since then, most visual scientists have assumed that eye vergence plays an important role both in judging absolute distance and for scaling retinal size and binocular disparities. In contrast, al-Haytham's and Gibson's "ground theories," which are based on the geometry of the textured ground plane surface that has surrounded us throughout evolution and during our lifetimes, are not just more ecologically based but they also obviate the need for disparity scaling.

Tracking Perceptual Depth with Eye Vergence Movements in Real World, Augmented Reality, and Virtual Reality Environments

Tracking Perceptual Depth with Eye Vergence Movements in Real World, Augmented Reality, and Virtual Reality Environments

Moderate Severity SARS-CoV-2 (COVID-19) Affects Ocular Vergence Indices: Eye Tracking-Based Study.

Since the start of the SARS-CoV-2 (COVID-19) pandemic, it has become clear that the brain is one of the main targets for acute and chronic damage. Although neurodegenerative changes have yet to be investigated, there is already a large body of data on damage to its fiber tracts. A mobile eye tracker is possibly one of the best tools to study such damage in a COVID hospital setting. At the same time, the available data indicate that eye tracking parameters, even in healthy volunteers, demonstrate a distinct gender-specific difference.The aim of the work is to evaluate functional and structural impairments of the fiber tracts and to find possible gender-specific dynamics of eye tracking indicators in the acute period of COVID-19 pneumonia (Delta variant) of moderate severity. A single-center non-randomized retrospective study included 84 patients in the acute period of moderate severity SARS-CoV-2 (COVID-19) pneumonia (Delta variant) (Group 1). The mean time from admission was 1.4±1.2days. M:41, F:43. According to thoracic CT, the lung involvement ranged from CT 1 to CT 2. SpO2 ranged from 95% to 99%. The mean age was 35.5±14.8years (from 18 to 60). The control group (Group 2) included 158 healthy volunteers without pathology of the vision organs and central nervous system.The eye vergence index (VRx) was determined using eye tracking as a motion correlation coefficient between the angular velocities of the left and right eyeballs and was a measure of the conjugation of horizontal and vertical eye movements.The mobile complex Eye Tracker Low-Speed 20 (BVG LLC, the Netherlands) was used. Eye tracking parameters were assessed by vertical and horizontal eye vergence (VVRx and HVRx).Statistical analysis was done using the methods of parametric and non-parametric statistics. Moderate COVID-19 pneumonia resulted in a significant decrease in both VVRx and HVRx compared to controls (0.763±0.127 and 0.856±0.043; p<0.000001; 0.729±0.018 and 0.776±0.023 p<0.000001, respectively). VVRx values were significantly higher in men (0.775±0.046 and 0.747±0.091, p=0.019, respectively), while ХVRx values were significantly higher in women (0.665±0.018 and 0.728±0.024, p<0.0000001, respectively). SARS-CoV-2 (COVID-19) of moderate severity is accompanied by a significant deterioration in eye tracking performance proving functional and structural impairments (p<0.05). VVRx was significantly higher in men, and HVRx was substantially greater in women reflecting gender-specific differences.

Ultralow Power On-the-Eye Vergence and Distance Sensing Through Differential Magnetometry

We demonstrate the realization of a very low energy, on-the-eye vergence-type distance ranger based on sensing of a locally-uniform vector field, specifically the earth’s magnetic field. This ranging method is passive, only requiring measurement of the magnetic field vector at both eyeballs utilizing magnetometer chips placed on the eye scleral regions. The eye vergence angle and range distance are calculated from these two vector quantities. The method can obtain a range reading with as little as 118 nJ of energy consumed per eye for 3.3V and 50 nJ when operated at 1.9V. This method is thus suitable for applications where energy storage is very limited such as in smart contacts vision correcting microsystems.

Tracking Perceptual Depth Changes with Eye Vergence and Inter Pupillary Distance in a Virtual Reality Environment

Tracking Perceptual Depth Changes with Eye Vergence and Inter Pupillary Distance in a Virtual Reality Environment

Effects of virtual target size, position, and parallax on vergence-accommodation conflict as estimated by actual gaze

Due to the increased utilization of stereoscopic displays, the scope of the vergence–accommodation conflict has been studied extensively to reveal how the human visual system operates. The purpose of this work was to study the phenomenon of vergence–accommodation conflict by comparing the theoretical eye vergence angle (vergence response) and gaze-based eye vergence angle (vergence stimulus) based on eye tracker gaze data. The results indicated that the gaze-based eye vergence angle was largest at the greatest parallax. The result also revealed that the eye vergence angle accuracy was significantly highest at the nearest parallax. Generally, accuracy improves when virtual objects are put in the middle and close to participants' positions. Moreover, the signed error decreases significantly when the virtual object is in the middle. Based on the results of this study, we can gain a greater understanding of the vergence–accommodation conflict in the stereoscopic environment.

Atypical cognitive vergence responses in children with attention deficit hyperactivity disorder but not with autism spectrum disorder in a facial emotion recognition task

Facial expression of emotion is fundamental to human social interactions. Attention to relevant cues in ADHD and ASD patients are believed to underlie difficulties in recognizing emotions. Cognitive vergence eye movements during gaze fixation have a role in attention. Here we evaluate a possible role of cognitive vergence in facial emotion recognition. We recorded eye vergence from children with ADHD (n ​= ​27), ASD (n ​= ​18) or ADHD&ASD (n ​= ​15) and from neurotypical (NT; n ​= ​31) children during a facial emotion recognition task. Vergence responses to relevant stimuli were stronger than those to distractor stimuli. ADHD and ADHD&ASD children showed shorter gaze fixation duration and weaker cognitive vergence responses to the eye regions of the face stimuli compared to neurotypically developing children. In contrast, gaze behavior and vergence responses of ASD children resembled that of neurotypically developing children. These results provide evidence for the idea that impaired recognition of facial expression of emotion is a problem of attending the relevant cues to adequately recognize facial expressions. As ASD patients resembled that of NT, cognitive vergence represents an etiological difference between ADHD and ASD.

Binocular vision: The relations among eye vergence, stereo correspondence, and retinal disparities

Binocular vision: The relations among eye vergence, stereo correspondence, and retinal disparities

HiddenGazeStereo: Hiding Gaze-Contingent Disparity Remapping for 2D-Compatible Natural 3D Viewing

Stereoscopic 3D displays (S3D), the most popular consumer display devices for 3D presentation, have a few problems that degrade the natural visual experience, such as unnatural relationships between eye vergence and accommodation, and severe image blurring (ghost) for viewers without stereo glasses. To simultaneously solve these problems, we combine gaze-contingent disparity remapping with Hidden Stereo in a manner that mutually compensates for their respective shortcomings. Gaze-contingent disparity remapping can reduce the vergence-accommodation conflict by shifting the disparity distribution around the gaze position to be centered on the display plane. Hidden Stereo can synthesize 2D-compatible 3D stereo images that do not produce any ghosting artifacts when the images for the two eyes are linearly fused. Thus, by using our new gaze-contingent display, while one viewer with glasses enjoys natural 3D content, many other glassless viewers enjoy clear 2D content. To enable real-time synthesis, we accelerate Hidden Stereo conversion by limiting the processing to each horizontal scanline. Through a user study using a variety of 3D scenes, we demonstrate that Hidden Stereo can effectively hide disparity information to glassless viewers despite the dynamic disparity manipulations. Moreover, we show that our method can alleviate the limitation of Hidden Stereo—the narrow reproducible disparity range—by manipulating the disparity so that the depth information around the gaze position is maximally preserved.

Soft, wireless periocular wearable electronics for real-time detection of eye vergence in a virtual reality toward mobile eye therapies.

Recent advancements in electronic packaging and image processing techniques have opened the possibility for optics-based portable eye tracking approaches, but technical and safety hurdles limit safe implementation toward wearable applications. Here, we introduce a fully wearable, wireless soft electronic system that offers a portable, highly sensitive tracking of eye movements (vergence) via the combination of skin-conformal sensors and a virtual reality system. Advancement of material processing and printing technologies based on aerosol jet printing enables reliable manufacturing of skin-like sensors, while the flexible hybrid circuit based on elastomer and chip integration allows comfortable integration with a user's head. Analytical and computational study of a data classification algorithm provides a highly accurate tool for real-time detection and classification of ocular motions. In vivo demonstration with 14 human subjects captures the potential of the wearable electronics as a portable therapy system, whose minimized form factor facilitates seamless interplay with traditional wearable hardware.

Eye vergence responses in children with and without reading difficulties during a word detection task

Vergence eye movements are movements of both eyes in opposite directions. Vergence is known to have a role in binocular vision. However recent studies link vergence eye movements also to attention and attention disorders. As attention may be involved in dyslexia, it is sensible to guess that the presence of reading difficulties can be associated with specific patterns in vergence responses. Data from school children performing a word-reading task have been analysed. In the task, children had to distinguish words from non-words (scrambled words or row of X’s), while their eye positions were recorded. Our findings show that after stimulus presentation eyes briefly converge. These vergence responses depend on the stimulus type and age of the child, and are different for children with reading difficulties. Our findings support the idea of a role of attention in word reading and offer an explanation of altered attention in dyslexia.

Role of vergence eye movements in the visual recognition of long time duration.

When viewing dichoptic stimuli in long time duration, visual percepts are always the alternation between the left and right eye inputs, while not the combination. This is known as binocular rivalry. An efficient coding theory reported that binocular visual inputs can be combined into binocular summation (S+) and difference (S-) channels in V1 brain area. In this study, we used specially designed stimuli as the previous study, in which monocular inputs caused ambiguous percepts, but S+ and S- channels had unambiguous percepts. We aim to investigate whether the visual percepts alter between S+ and S- channels in long time duration and whether vergence eye movements are involved in the process. To do so, the stimuli were presented in 300-s time duration in a trial, and a binocular eye tracker was used to record eye information. Participants' real-time behavioral responses about the visual percepts and binocular information were recorded simultaneously. The results show there are perceptual flips between S+ and S- channels in both central and long time viewing conditions. More importantly, in central vision there are vergence eye movements before perceptual flips, suggesting the involvement of high level visual attention; the time of a perceptual flip from S+ is shorter than that of a flip from S-, which might be due to different involvements of visual attention, indicating a bias of feedback connection from higher brain areas for visual attention to S+ channel. Since S+ and S- dominated signals can be carried by different types of binocular neurons, our results provide new insights into high level visual attention and binocular neurons in V1 brain area by using specially designed dichoptic stimuli and eye vergence as measuring tools.

Eye Vergence Responses During an Attention Task in Adults With ADHD and Clinical Controls

Objective: ADHD patients show poor oculomotor control and recent studies show that attention-related eye vergence is weak in ADHD children. We aimed to assess vergence as a potential diagnostic biomarker for ADHD in adults. Method: We assessed the modulation in the angle of vergence while performing an attention task (N = 144), comparing the results for adults previously diagnosed with ADHD (N = 108) with age-matched clinical controls (N = 36). Results: Significant differences in eye vergence response modulation between clinical controls and ADHD patients were documented. Diagnostic test accuracy was 79%. Conclusion: In combination with an attention task, eye vergence responses could be used as an objective marker to support the clinical diagnosis of adult ADHD.

Changes in the disparity vergence main sequence after treatment of symptomatic convergence insufficiency in children

This study investigates the underlying physiological mechanisms that may lead to improved outcomes for symptomatic convergence insufficiency (CI) patients after 12 weeks of office-based vergence/accommodation therapy (OBVAT) by evaluating the change in the main sequence of vergence and saccadic eye movements. In this prospective trial, 12 participants with symptomatic CI were recruited and treated with 12 weeks of OBVAT. Outcome measures included the objective assessment of the following: peak velocity, time to peak velocity, latency, response amplitude, and clinical changes in the near point of convergence (NPC), positive fusional vergence (PFV) and symptoms via the Convergence Insufficiency Symptom Survey (CISS). Ten of the twelve participants (83%) were categorized as “successful” and two were “improved” based on pre-determined published criteria (CISS, NPC, PFV). There were statistically significant changes in peak velocity, time to peak velocity, and response amplitude for both 4° and 6° symmetrical convergence and divergence eye movements. There was a significant change in the main sequence ratio for convergence post-OBVAT compared to baseline measurements (P=0.007) but not for divergence or saccadic responses. Phasic/step vergence movements adjust the underlying neural control of convergence and are critical within a vision therapy program for CI patients.

Gazing into Space: Systematic biases in determining another’s fixation distance from eye vergence

Gazing into Space: Systematic biases in determining another’s fixation distance from eye vergence