Vergence Movements Research Articles

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

Muscles that move the retina augment compound eye vision in Drosophila.

Most animals have compound eyes, with tens to thousands of lenses attached rigidly to the exoskeleton. A natural assumption is that all of these species must resort to moving either their head ortheir body to actively change their visual input. However, classic anatomy has revealed that flies have muscles poised to move their retinas under the stable lenses of each compound eye1-3. Here we show that Drosophila use their retinal muscles to smoothly track visual motion, which helps to stabilize the retinal image, and also to perform small saccades when viewing a stationary scene. We show that when the retina moves, visual receptive fields shift accordingly, and that even the smallest retinal saccades activate visual neurons. Using a head-fixed behavioural paradigm, we find that Drosophila perform binocular, vergence movements of their retinas-which could enhance depth perception-when crossing gaps, and impairing the physiology of retinal motor neurons alters gap-crossing trajectories during free behaviour. That flies evolved an ability to actuate their retinas suggests that moving the eye independently of the head is broadly paramount for animals. The similarities of smooth and saccadic movements of the Drosophila retina and the vertebrate eye highlight a notable example of convergent evolution.

Fast non-invasive measures of binocular visual processes relevant to virtual environments

Precise coordination of many visual processes is required for clear and precise binocular viewing. However, few studies have measured these binocular processes across large samples to examine how they may differ. The two aims of the experiment were to develop new, fast and non-invasive tests for several binocular visual processes and to administer these tests to a large sample. The tests were designed to obtain thresholds of performance for vergence movement duration, latency, and range, fusion range, and static stereoacuity. Thresholds were obtained using a staircase procedure, with a two-alternative forced-choice paradigm in each staircase, which was chosen to minimise the number of trials required. The stimuli were presented stereoscopically in a mirror stereoscope, with subjective perceptions of nonius lines and static random dot stereograms as the measures of interest. The tests were administered to a sample of 108 participants and demonstrated marked variability in threshold performance within each test. These thresholds are compared to findings in previous research, and consequences for virtual reality design are explored.

Disconjugate Eye Movements in Dyslexic Adolescents While Viewing Op Art: A Creative Handicap?

Op art was created, in part, to produce illusions of movement. Given that dyslexics have been shown to have impaired visuo-postural axis deficits, it may be possible that dyslexics see illusions different than their non-dyslexic peers. To test this theory, we measured eye movement and posture in 47 dyslexic (18 female, 29 male; mean age 15.4) and 44 non dyslexic (22 female, 22 male; mean age 14.8) adolescents while they viewed three works of art by Op artist Bridget Riley. They then responded to a questionnaire about how they felt while viewing the artworks. Dyslexics demonstrated significantly slower saccades in terms of average velocity that was particularly disturbed in paintings that manipulated depth. Subjectively, dyslexics felt much more destabilized compared to their peers; however, there was not a significant difference in objective postural measurements between the two groups. The sensation of destabilization was positively correlated with appreciation in non-dyslexic adolescents. These subjective results suggest that dyslexics may be more sensitive to movement in depth, which could be related to the instability in vergence movements. Whereas this instability represents a hinderance in relation to reading, it could be an advantage while viewing paintings such as these.

Loss of audiovisual facilitation with age occurs for vergence eye movements but not for saccades

Though saccade and vergence eye movements are fundamental for everyday life, the way these movements change as we age has not been sufficiently studied. The present study examines the effect of age on vergence and saccade eye movement characteristics (latency, peak and average velocity, amplitude) and on audiovisual facilitation. We compare the results for horizontal saccades and vergence movements toward visual and audiovisual targets in a young group of 22 participants (mean age 25 ± 2.5) and an elderly group of 45 participants (mean age 65 + 6.9). The results show that, with increased age, latency of all eye movements increases, average velocity decreases, amplitude of vergence decreases, and audiovisual facilitation collapses for vergence eye movements in depth but is preserved for saccades. There is no effect on peak velocity, suggesting that, although the sensory and attentional mechanisms controlling the motor system does age, the motor system itself does not age. The loss of audiovisual facilitation along the depth axis can be attributed to a physiologic decrease in the capacity for sound localization in depth with age, while left/right sound localization coupled with saccades is preserved. The results bring new insight for the effects of aging on multisensory control and attention.

Effects of Parkinson Disease on Blur-Driven and Disparity-Driven Vergence Eye Movements.

Synchronous movements of the 2 eyes in the opposite direction, disconjugate movements such as vergence, facilitate depth perception. The vergence eye movements are affected in Parkinson disease (PD). Visual blur (accommodation) and fusion (retinal disparity) are important triggers for the vergence. The neural circuit responsible for blur-driven and disparity-driven vergence is tightly coupled. We investigated the effect of PD on these 2 vergence paradigms. In the experiment involving 14 patients with PD and 6 healthy controls, substantial differences between blur-driven and disparity-driven vergence were found. The gain (ratio of actual vs desired eye movements) was reduced in patients with PD in case of disparity-driven vergence but not in blur-driven vergence. The latency of disparity-driven vergence onset was significantly longer for patients with PD compared with healthy controls. Four strategies were used to drive disparity-driven vergence: a) pure disconjugate vergence, b) conjugate saccadic movements, c) disconjugate vergence followed by saccadic movements, and d) conjugate saccades followed by disconjugate vergence movements. Blur-driven vergence had only 2 strategies: a) conjugate saccades followed by disconjugate vergence and b) conjugate saccadic movements only. The results are consistent with the prediction that PD primarily affects disparity-driven vergence, but there are some effects on the strategies to execute blur-driven vergence. We speculate that the deep cerebellar nuclei and the supraoculomotor area of the midbrain that carry the disparity-driven and blur-driven vergence are affected in PD. It is possible to modulate their function through projections to the subthalamic nuclei.

Predicting Dyslexia and Reading Speed in Adolescents from Eye Movements in Reading and Non-Reading Tasks: A Machine Learning Approach.

There is evidence that abnormalities in eye movements exist during reading in dyslexic individuals. A few recent studies applied Machine Learning (ML) classifiers to such eye movement data to predict dyslexia. A general problem with these studies is that eye movement data sets are limited to reading saccades and fixations that are confounded by reading difficulty, e.g., it is unclear whether abnormalities are the consequence or the cause of reading difficulty. Recently, Ward and Kapoula used LED targets (with the REMOBI & AIDEAL method) to demonstrate abnormalities of large saccades and vergence eye movements in depth demonstrating intrinsic eye movement problems independent from reading in dyslexia. In another study, binocular eye movements were studied while reading two texts: one using the “Alouette” text, which has no meaning and requires word decoding, the other using a meaningful text. It was found the Alouette text exacerbates eye movement abnormalities in dyslexics. In this paper, we more precisely quantify the quality of such eye movement descriptors for dyslexia detection. We use the descriptors produced in the four different setups as input to multiple classifiers and compare their generalization performances. Our results demonstrate that eye movement data from the Alouette test predicts dyslexia with an accuracy of 81.25%; similarly, we were able to predict dyslexia with an accuracy of 81.25% when using data from saccades to LED targets on the Remobi device and 77.3% when using vergence movements to LED targets. Noticeably, eye movement data from the meaningful text produced the lowest accuracy (70.2%). In a subsequent analysis, ML algorithms were applied to predict reading speed based on eye movement descriptors extracted from the meaningful reading, then from Remobi saccade and vergence tests. Remobi vergence eye movement descriptors can predict reading speed even better than eye movement descriptors from the meaningful reading test.

Dyslexics' Fragile Oculomotor Control Is Further Destabilized by Increased Text Difficulty.

Dyslexic adolescents demonstrate deficits in word decoding, recognition, and oculomotor coordination as compared to healthy controls. Our lab recently showed intrinsic deficits in large saccades and vergence movements with a Remobi device independent from reading. This shed new light on the field of dyslexia, as it has been debated in the literature whether the deficits in eye movements are a cause or consequence of reading difficulty. The present study investigates how these oculomotor problems are compensated for or aggravated by text difficulty. A total of 46 dyslexic and 41 non-dyslexic adolescents’ eye movements were analyzed while reading L’Alouette, a dyslexia screening test, and 35 Kilos D’Espoir, a children’s book with a reading age of 10 years. While reading the more difficult text, dyslexics made more mistakes, read slower, and made more regressive saccades; moreover, they made smaller amplitude saccades with abnormal velocity profiles (e.g., higher peak velocity but lower average velocity) and significantly higher saccade disconjugacy. While reading the simpler text, these differences persisted; however, the difference in saccade disconjugacy, although present, was no longer significant, nor was there a significant difference in the percentage of regressive saccades. We propose that intrinsic eye movement abnormalities in dyslexics such as saccade disconjugacy, abnormal velocity profiles, and cognitively associated regressive saccades can be particularly exacerbated if the reading text relies heavily on word decoding to extract meaning; increased number of regressive saccades are a manifestation of reading difficulty and not a problem of eye movement per se. These interpretations are in line with the motor theory of visual attention and our previous research describing the relationship between binocular motor control, attention, and cognition that exists outside of the field of dyslexia.

Characteristics of saccades during the near point of convergence test

The near point of convergence test is widely used to evaluate binocular vision. It assesses the ability of the eyes to converge at short distances. Although the test consists of a pure symmetrical vergence task, small involuntary saccades occur concurrently. The main goal of this study was to analyze saccadic characteristics as a function of vergence demand when testing the near point of convergence. To this purpose, the eye movements of 11 participants were registered with an eye-tracker while they performed the near point of convergence test by following a target that traveled forward and backward on a motorized bench. Saccade amplitude increased and, on average, saccade rate decreased with vergence demand. In general, the direction of the concurrent vergence movement had no significant effect on saccade characteristics. However, each individual subject showed idiosyncratic behavior. Most saccades tended to be corrective in terms of both binocular disparity and individual fixation position errors. In particular, most participants tended to correct the fixation position error of the dominant eye.

Blast mild traumatic brain injury is associated with increased myopia and chronic convergence insufficiency

While chronic visual symptom complaints are common among Veterans with a history of mild traumatic brain injury (mTBI), research is still ongoing to characterize the pattern of visual deficits that is most strongly associated with mTBI and specifically, the impact of blast-related mTBI on visual functioning. One area that has not been well explored is the potential impact of blast mTBI on refractive error. While myopic shifts have been documented following head injuries in civilian populations, posttraumatic myopic shifts have not been explored in participants with military mTBI. This study investigated the impact of blast mTBIs on a range of visual function measures including distance acuity and refractive error, in a well-characterized cohort of thirty-one Post-9/11 veterans for whom detailed clinical interviews regarding military and TBI history were available. Seventeen participants had a history of blast-related mTBI (blast mTBI + group) while 14 did not (blast mTBI- group). Results show an increased frequency of convergence insufficiency and myopia in the blast mTBI + group relative to the blast mTBI- group. Linear regression analyses further show that deficits in distance acuity and refractive error are associated with the number of blast mTBIs during military service but not the number of non-blast mTBIs or the number of lifetime non-blast TBIs and cannot be accounted for by PTSD. These results are consistent with long-lasting damage following blast mTBI to subcortical visual structures that support both vergence movements and the accommodative functions needed to see clearly objects at varying distances.

The vergence horopter

The horopter is defined by the criterion with which it is measured; these include the apparent frontoparallel plane, the region of binocular single vision, and identical visual direction. Another criterion is one that “the positions of the points are such that none provides a stimulus for fusional movement of the eyes”. Measuring the horopter using this criterion is the aim of the current paper. Based on previous research investigating corresponding points, we predicted the vergence horopter should trace an arc similar to the empirical horizontal horopter. We further predicted based on the characteristics of vergence eye movements in the periphery, that the range of horizontal disparities that do not elicit a vergence movement would increase with eccentricity. In experiment 1 we conducted the first measurements of the vergence horopter along the horizontal plane of regard and sagittal planes. We found that the vergence horopter consists of a stable range of disparities that do not increase with eccentricity. In experiment 2, we measured Panum’s fusional range for the same eccentricities and elevations to determine the placement of the vergence horopter within the fusional ranges. In the horizontal plane, the vergence horopter sits centrally within Panum’s fusional range. In the vertical plane, the data are suggestive that the vergence horopter is less slanted than the corresponding fusional range.

Differential Impact Of Sound On Saccades Vergence And Combined Eye Movements: A Multiple Case Study

Most of the previous literature regarding eye movements use visual stimuli alone. However, in real life, visual and auditory stimuli occur together frequently. It has been shown that a sound presented just before or simultaneously with the visual target reduces the latency of the saccades. The present study investigates the effect of a sound presented shortly before the LED visual target for three types of eye movements: saccades, vergences and combined eye movements. Fourteen participants (6 women, mean age: 22.6 +/- 0.62 years) took part in the study. Each type of eye movements was tested in two conditions: one with visual LED targets alone, the other with a sound coming for a buzzer adjacent to the LED, and preceding by 50 ms the onset of the LED target (auditory-visual target). Eye movements were recorded at 220 Hz for each eye with the Eyeseecam binocular devicehttps://www.eyeseetec.de/eyeseecam-sci/). The results confirm that the sound significantly reduces the latency of the saccades. In contrast, for convergence or divergence the sound did not decrease the latency but it did increase the velocity and reduced the duration of such movements significantly. For combined saccade vergence movements particularly leftward, the sound had multiple effects on the saccade component: it decreased the duration of the saccade component and reciprocally increased its velocity but also reduced its latency. Such mixed effects on latency duration and velocity of the saccade component favor the hypothesis that saccade components of combined eye movements are subtended by a co-activation of both, saccade and vergence brainstem generators. The differential benefit from the sound according to the type of eye movements is of theoretical and clinical interest.

Perceptual effects of unequal saccadic adaptation produced by a dichoptic step.

The binocular coordination of eye movements in a three-dimensional environment involves a combination of saccade and vergence movements. To maintain binocular accuracy and control in the face of sensory and motor changes (that occur with e.g., normal aging, surgery, corrective lenses), the oculomotor system must adapt in response to manifest visual errors. This may be achieved through a combination of binocular and monocular mechanisms, including the recalibration of saccade and vergence amplitudes in response to different visual errors induced in each eye (Maiello, Harrison, & Bex, 2016). This work has used a double-step paradigm to recalibrate eye movements in response to visual errors produced by dichoptic target steps (e.g., leftward in the left eye and rightward in the right eye). Here, we evaluated the immediate perceptual effects of this adaptation. Experiment 1 measured localization errors following adaptation by comparing the apparent locations of pre- and postsaccadic probes. Consistent with previous work showing localization errors following saccadic adaptation, our results demonstrated that adaptation to a dichoptic step produces different localization errors in the two eyes. Furthermore, in Experiment 2, this effect was reduced for a vergence shift in the absence of a saccade, indicating that saccade programming is responsible for a large component of this illusory shift. Experiment 3 measured postsaccadic stereopsis thresholds and indicated that, unlike localization judgments, adaptation did not influence stereoacuity. Together, these results demonstrate novel dichoptic visual errors following oculomotor adaptation and point to monocular and binocular mechanisms involved in the maintenance of binocular coordination.

Vergence and accommodation disorders in children with vertigo: A need for evidence-based diagnosis

BackgroundPrevious clinical evaluations have demonstrated a difference in eye movements in healthy children compared to children with vertigo without vestibular pathology. It has also been previously shown that accommodation and vergence responses can be measured with remote haploscopic photo refractor (RHP) devices. We have developed a method, called REMOBI (patent US8851669, WO2011073288) that allows us to test eye movements in three-dimensional space without decoupling vergence and accommodation.[1]. MethodsWe compared standard clinical testing of vergence and accommodation responses separately, with laboratory simultaneous measurement of vergence and accommodation in healthy children, 31 with vertigo (mean age 11 SD +/- 3.02), and 53 without (mean age 10 SD +/- 3.29). Children diagnosed with vertigo then underwent orthoptic rehabilitation for vergence and accommodation disorders and were re-evaluated twice using laboratory testing: once after 12 sessions and once 3-months after completing the sessions. FindingsUsing the clinical tests, significant differences were found between the vertigo and healthy groups: D’ (break point of divergence near), D2 (second measurement of divergence after convergence far), D2’ (second measurement of divergence after convergence near), C (break point of convergence far), and C’ (break point of convergence near). However, no significant differences in accommodation or vergence were seen between the two groups using laboratory tests (RHP and REMOBI). Further, there was no difference in laboratory measurements in children with vertigo before, after, and 3 months after clinical rehabilitation. InterpretationWe postulate the difference in these two tests is because the laboratory tests are more accurate and more realistic because they measure accommodation and vergence simultaneously, as it incorporates a stronger binocular coordination response not appreciated by current clinical measurements. Further studies should be conducted to evaluate whether clinicians should consider adding objective measurements, such as using a RHP device, when diagnosing patients with vergence and accommodation disorders, to avoid prescribing costly and timely rehabilitation programs that do not improve accommodative and vergence movements. FundingWe thank the Fulbright Foundation, along with the University of California, San Francisco, for the research fellowship to Lindsey M Ward. This study is part of the PHRC VERVE, hospital research program, run at the hospital Robert Debré and supported by Direction de la Recherche Clinique, Assistance Publique, France. The funding sources had no involvement in the study design; collection, analysis, and interpretation of data; writing of the manuscript; and in the decision to submit the manuscript for publication.

Vergence Eye Movements: From Basic Science to Clinical Application - Foreword to the Special Issue.

The abstract book of the last European Conference on Eye Movements [1] lists abstracts of 373 presentations, but less than five percent investigate vergence eye movements, i.e. the coordination of the right and left eye. Why then a special issue on this neglected issue? Human vision under natural conditions involves both eyes in coordination controlled by interacting processes subsumed under the concept of vergence.. Further, vergence is important for people in their daily lives since disorders of vergence can have serious consequences: ophthalmologists deal with squinting patients on the basis of heterophoria and heterotropia testing, eye strain or visual complaints can be related to impaired vergence dynamic or less accurate static vergence, remediation by optometrist includes vergence training or prism eye glasses, etc.

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.

Dynamics of the disparity vergence fusion sustain component

The stereotypical vergence response to a step stimulus consists of two dynamic components: a high velocity fusion initiating component followed by a slower component that may mediate sustained fusion. The initial component has been well-studied and is thought to be controlled by an open-loop mechanism. Less is known about the slow, or fusion sustaining component except that it must be feedback controlled to achieve the positional precision of sustained fusion. Given the delays in disparity vergence control, a feedback control system is likely to exhibit oscillatory behavior. Vergence responses to 4 deg step changes in target position were recorded in eight subjects. The slow component of each response was isolated manually using interactive graphics and the frequency spectrum determined. The frequency spectra of all isolated slow vergence movements showed a large low frequency peak between 1.0 and 2.0 Hz and one or more higher frequency components. The higher frequency components were found to be harmonics of the low frequency oscillation. A feedback model of the slow component was developed consisting of a time delay, an integral/derivative controller and an oculomotor plant based on Robinson’s model. Model simulations showed that a direction dependent asymmetry in the derivative element was primarily responsible for the higher frequency harmonic components. Simulations also showed that the base frequencies are primarily dependent on the time delay in the feedback control system. The fact that oscillatory behavior was found in all subjects provides strong support that the slow, fusion sustaining component is mediated by a feedback system.

Relative contributions to vergence eye movements of two binocular cues for motion-in-depth

When we track an object moving in depth, our eyes rotate in opposite directions. This type of “disjunctive” eye movement is called horizontal vergence. The sensory control signals for vergence arise from multiple visual cues, two of which, changing binocular disparity (CD) and inter-ocular velocity differences (IOVD), are specifically binocular. While it is well known that the CD cue triggers horizontal vergence eye movements, the role of the IOVD cue has only recently been explored. To better understand the relative contribution of CD and IOVD cues in driving horizontal vergence, we recorded vergence eye movements from ten observers in response to four types of stimuli that isolated or combined the two cues to motion-in-depth, using stimulus conditions and CD/IOVD stimuli typical of behavioural motion-in-depth experiments. An analysis of the slopes of the vergence traces and the consistency of the directions of vergence and stimulus movements showed that under our conditions IOVD cues provided very little input to vergence mechanisms. The eye movements that did occur coinciding with the presentation of IOVD stimuli were likely not a response to stimulus motion, but a phoria initiated by the absence of a disparity signal.

Size matters: How reaching and vergence movements are influenced by the familiar size of stereoscopically presented objects.

The knowledge about the usual size of objects—familiar size—is known to be a taken into account for distance perception. The influence of familiar size on action programming is less clear and has not yet been tested with regard to vergence eye movements. In two experiments, we stereoscopically presented everyday objects, such as a credit card or a package of paper tissues, and varied the distance as specified by binocular disparity and the distance as specified by familiar size. Participants had to fixate the shown object and subsequently reach towards it either with open or with closed eyes. When binocular disparity and familiar size were in conflict, reaching movements revealed a combination of the two depth cues with individually different weights. The influence of familiar size was larger when no visual feedback was available during the reaching movement. Vergence movements closely followed binocular disparity and were largely unaffected by familiar size. In sum, the results suggest that in this experimental setting familiar size is taken into account for programming and executing reaching movements while vergence movements are primarily based on binocular disparity.

A Rhesus Monkey With a Naturally Occurring Impairment of Disparity Vergence. II. Abnormal Near Response Cell Activity in the Supraoculomotor Area.

PurposeConvergence insufficiency is a very common disorder that can have significant adverse effects on school performance. When reading, children with this disorder often experience diplopia and headaches. We have recently obtained a rhesus monkey with a naturally occurring impairment of vergence eye movements. In the companion paper, we report behavioral testing that shows a pattern of impairments similar to what clinicians observe in human children with convergence insufficiency, including a receded near point, an exophoria that increases as target distance decreases, and difficulty maintaining an appropriate vergence angle when presented with a large field stimulus at near. For the present case report, we wondered whether these behavioral deficits would be associated with abnormal discharge patterns in brainstem neurons related to vergence eye movements.MethodsSingle unit activity was recorded from near and far response cells in the supraoculomotor area in the vergence-impaired monkey, while he performed a smooth vergence tracking task or fixated visual targets at different distances.ResultsWe found an abnormally weak sensitivity to both vergence angle and vergence velocity. Nonetheless, these neurons modulated in association with contextually inappropriate slow vergence movements that occurred in the absence of saccades but not for slow divergence drifts that immediately followed converging saccades. Modulation of activity was more robust when additional depth cues were available.ConclusionsThese data suggest that disorders affecting vergence eye movements may be associated with impoverished sensory input to the near and far response cells and, perhaps, aberrant tuning in vergence-related neurons.