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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.

To evaluate foveation dynamics and characteristics of vergence eye movements during fixation of static targets at different distances and while tracking a target moving in depth in a subject with congenital nystagmus (CN). Eye movements of a well-studied subject with CN were recorded using the magnetic search coil technique and analyzed using the OMtools software, including the eXpanded Nystagmus Acuity Function (NAFX). Both the phase planes and NAFX values during fixation of targets at various near distances were equivalent to those during fixation of a far target. When applied to vergence data, the NAFX values (“binocular” NAFX) were higher than for the individual eye data. Vergence tracking of targets moving in depth was demonstrated and was accurate for targets moving at speeds up to ~ 35°/sec. Target foveation qualities during fixation of targets at various near distances were equivalent to that during fixation of a far target. Stereo discrimination was limited by the foveation quality of the eye with the higher NAFX waveform. Foveation period slopes during vergence tracking demonstrated vergence movements despite the ongoing CN oscillation. Similar to what we found with fixation, pursuit, and the vestibulo-ocular systems, these findings establish that vergence in both static and dynamic viewing conditions functions normally in the presence of the CN oscillation.

Supported by NIH EY018875 (AMN), BBSRC grants BB/M001660/1 (JH), BB/M002543/1 (AW), and BB/MM001210/1 (MB). 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. Publisher PDF

The abstract book of the last European Conference on Eye Movements (Martinez-Conde, Martinez-Otero, Compte, & Groner, 2019) 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. What are the reasons why processes of vergence are underestimated in our scientific community? The main reason seems to be the fact that the two eyes must be analysed separately with high precision. The differences between the measured two eye positions are typically relatively small and often at the limit of the recording systems. The question arises: Are the difference in the measurements due to noise, to error, or due to physiological processes? A further difficulty arises from the individual differences between observers. Thus, a vergence researcher has a rather difficult job in critically evaluating the eye tracker technology and taking into account different scientific areas like ophthalmology, optometry, psychology, and using adequate statistical analyses. This kind of research requires a multidisciplinary perspective. In this special issue, three studies concentrated on the methodology of measuring vergence. An established clinical method is the prism cover test, which measures the heterophoria, i.e. the misalignment of the visual axes under monocular viewing conditions compared to binocular fixation. Paulus, Straube & Eggert (2019) developed an automated alternating cover test based on a combination of video-oculography and shutter glasses which minimizes stimulus noise and has a defined measurement noise. The total variance of the measurement is composed of components related to the observer, to the size of the heterophoria and to the availability of sensory vergence cues. Paulus et al. (2019) examined these factors and found that a major component of the within-subject variance of the manual prism cover test is due to the variability in the manifest heterophoria of the tested persons. Wang, Holmqvist, & Alexa (2019) define a point of interest in binocular viewing, which is the intersection point of the two lines of sight in three-dimensional space, or – more precisely - the point closest to the two lines of sight. By means of theoretical simulations compared to empirical recordings they demonstrated a bias of the vergence distance depending on the noise of the tracked eye position. The authors propose mathematical models of calibration as part of the analysis of the experimental data. Yaramothu, Jaswal & Alvarez (2019) measured vergence velocity and latency for step responses and found that eccentric circles with 6° eccentricity resulted in a faster response latency than a cross at central fixation. Their results have implications for the stimulus design in a variety of applications ranging from virtual reality to interventions in vision therapy. Vergence operates well within a limited physiological range; but when the limit of fusion is reached, single vision is lost and double vision occurs. McGinnis, I., Tierney, R., Mansell, J., & Phillips, J. (2019) measured the clinically established convergence fusion break point (near point of convergence, NPC) by shifting a target towards the eyes in three different velocities and varied the verbal instruction (“double” versus “blurry”). The statistical analysis resulted in significant differences in NPC for the two variables target speed and verbal instruction. A consequence of this study will be that the experimental conditions for examinations and research on NPC must be standardized with respect to the experimental variables investigated in this study. Dostalek, Hejda, Fliegel, Duchackova, Dusek, Hozman, Lukes & Autrata, R. (2019) investigated the fusion break point at a fixed test distance, but reduced the quality of the image in one eye by different modes (luminance contrast, higher-spatial frequency content, or luminance contrast plus higher-spatial frequency content). These modes had a certain influence, but the largest effect was the one of vergence demand, i.e. the absolute disparity of the two images. The authors argue that the image´s details (i.e. higher-spatial frequency content) protect binocular fusion from disruption under the lowest vergence demand. The dynamics of vergence responses to step stimuli includes two components, a high velocity fusion initiating component followed by a slower component that may mediate sustained fusion. The slow fusion-sustaining component was analysed by Semmlow and Alvarez (2019). This component was modelled by the authors as a feedback control system consisting of a time delay and an integral/derivative controller. The fast fusion-initiating component was explored by Scheiman, Yaramothu, & Alvarez (2019) by means of analysing the ratio of the velocity divided by the response amplitude. For convergent step stimuli, this ratio was affected by a vergence/accommodation training therapy. The study of Poffa and Joos (2019) used a traditional clinical method referred to as vergence facility: the examiner induces vergence responses by applying prisms and counts the number vergence movements per minute. This clinical measure was found to be related to fixations disparity, i.e. the static vergence error measured with an eye tracker. Comparing clinical test results with eye tracker recordings were included in the two studies which took also into account individual differences. Schroth, Joos, Alshuth & Jaschinski (2019) used a clinical nonius method for measuring the amount of the prism eye glass which is required to correct a fixation disparity (vergence error); this prism power was able to predict the prism-induced change in fixation disparity recorded with an eye tracker. Jainta and Joss (2019) tested the largest sample of subjects in this issue (n= 94) which allowed demonstrating the influence of the individual heterophoria on the binocular advantage, i.e. the extent to which during reading the fixation of a word is shorter in binocular than in monocular reading. The eye tracker measure of the heterophoria achieved superior results compared with subjective clinical measurements. The academic background of the present authors illustrates that vergence research is covered by different scientific disciplines including computer engineering, physics, optometry, ophthalmology and psychology. This has the advantage that vergence research benefits from the different approaches of these disciplines, given that a common language and mutual understanding is achieved. A common basis for such a multidisciplinary research could be the seminal book of Ian Howard (2012). This first special issue on vergence eye movements should give an overview of ongoing research in a relatively small scientific community and might motivate more relevant and multidisciplinary research, to be published in regular issues of the Journal of Eye Movement Research. References Dostalek, M., Hejda, J., Fliegel, K., Duchackova, M., Dusek, L., Hozman, J., Lukes, T., & Autrata, R. (2019). Influence of artificially generated interocular blur difference on fusion stability under vergence stress. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.4. Howard, I. P. (2012). Perceiving in Depth, Volume 1: Basic Mechanisms. New York: Oxford University Press, USA. Jainta, S., & Joss, J. (2019). Binocular advantages in reading revisited: attenuating effects of individual horizontal heterophoria. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.10. Martinez-Conde, S., Martinez-Otero, L., Compte, A., & Groner, R. (2019). Abstracts of the 20th European Conference on Eye Movements, 18-22 August 2019, in Alicante (Spain). Journal of Eye Movement Research, 12(7). https://doi.org/10.16910/jemr.12.7.1. McGinnis, I., Tierney, R., Mansell, J., & Phillips, J. (2019). The Effect of target speed and verbal instruction on NPC measures in a young, healthy, and active population. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.5. Paulus, M., Straube, A., & Eggert, T. (2019). Variance components affecting the repeatability of the alternating cover test. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.3. Poffa, R., & Joos, R. (2019). The influence of vergence facility on binocular eye movements during reading. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.9. Scheiman, M., Yaramothu, C., & Alvarez, T. (2019). Changes in the disparity vergence main sequence after treatment of symptomatic convergence insufficiency in children. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.6. Schroth, V., Joos, R., Alshuth, E., & Jaschinski, W. (2019). Short-term effects of aligning prisms on the objective and subjective fixation disparity in far distance. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.8. Semmlow, J.L., Yaramothu, C., & Alvarez, T.L. (2020). Dynamics of the disparity vergence slow (fusion sustaining) component. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.11. Wang, X., Holmqvist, K., & Alexa, M. (2019). The mean point of vergence is biased under projection. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.2. Yaramothu, C., Jaswal, R., & Alvarez, T. (2019). Target eccentricity and form influences disparity vergence eye movements responses: A temporal and dynamic analysis. Journal of Eye Movement Research, 12(4). https://doi.org/10.16910/jemr.12.4.7.

Figure-ground, that is the segmentation of visual information into objects and their surrounding backgrounds, provides structure for visual attention. Recent evidence shows a novel role of vergence eye movements in visual attention. In the present work, vergence responses during figure-ground segregation tasks are psychophysically investigated. We show that during a figure-ground detection task, subjects convergence their eyes. Vergence eye movements are larger in figure trials than in ground trials. In detected figures trials, vergence are stronger than in trials where the figure went unnoticed. Moreover in figure trials, vergence responses are stronger to low-contrast figures than to high-contrast figures. We argue that these discriminative vergence responses have a role in figure-ground.

Cel pracyW odniesieniu do choroby afektywnej dwubiegunowej (ChAD), dotychczasowe prace wskazują na zaburzenia ruchów sakadycznych, głównie pod postacią wydłużenia czasu reakcji (latencji) w testach prosakad i antysakad. Dotychczas nie przeprowadzono oceny ruchów wergencyjnych gałek ocznych u osób z ChAD. Głównym celem naszego badania jest ocena parametrów konwergencji (zbieżne ruchy gałek ocznych) w tej grupie klinicznej.MetodaDo badania włączono 30 pacjentów z ChAD w stanie remisji objawowej i 23 zdrowych ochotników. Uczestników poddano badaniu optometrycznemu oceniającemu punkt bliski konwergencji przy użyciu pręta fiksacyjnego. Badanie okulometryczne przeprowadzono przy pomocy okulografu wykorzystującego promieniowanie podczerwone z dedykowanym stymulatorem wergencji.WynikiPacjenci z ChAD wykazali istotnie większy średni błąd pozycji konwergencji do celu oraz większą liczbę wtrąceń sakadycznych w porównaniu do grupy kontrolnej. Analiza składowych głównych przeprowadzona na zmiennych okulometrycznych pokazała istotne różnice między pacjentami z ChAD a zdrowymi ochotnikami. Wykazano obecność istotnych korelacji między zaburzeniami ruchów wergencyjnych a liczbą wtrąceń sakadycznych.WnioskiPacjenci z ChAD ujawnili zaburzenia ruchów wergencyjnych gałek ocznych podobne do zaburzeń opisywanych w trakcie śledzenia bodźców poruszających się w płaszczyźnie czołowej. Podczas gdy zaburzenia wergencji były opisywane w innych zaburzeniach psychicznych, nasza praca po raz pierwszy obiektywnie zmierzyła to zjawisko w ChAD.

We stabilize the dynamic visual world on our retina by moving our eyes in response to motion signals. Coordinated movements between the two eyes are characterized as version when both eyes move in the same direction and vergence when the two eyes move in opposite directions. Vergence eye movements are necessary to track objects in three dimensions. In primates they can be elicited by intraocular differences in either spatial signals (disparity) or velocity, requiring the integration of left and right eye inputs. Whether mice are capable of similar behaviors is not known. To address this issue, we measured vergence eye movements in mice using a stereoscopic stimulus known to elicit vergence eye movements in primates. We found that mice also exhibit vergence eye movements, although at a low gain and that the primary driver of these vergence eye movements is interocular motion. Spatial disparity cues alone are ineffective. We also found that the vergence eye movements we observed in mice were robust to silencing visual cortex and to manipulations that disrupt the normal development of binocularity in visual cortex. A sublinear combination of motor commands driven by monocular signals is sufficient to account for our results. NEW & NOTEWORTHY The visual system integrates signals from the left and right eye to generate a representation of the world in depth. The binocular integration of signals may be observed from the coordinated vergence eye movements elicited by object motion in depth. We explored the circuits and signals responsible for these vergence eye movements in rodent and find these vergence eye movements are generated by a comparison of the motion and not spatial visual signals.

The Midas touch problem is a well-known problem in eye gaze interaction techniques. We present Verge-it as a Midas touch free input technique using modulated disparity vergence eye movement for a binocular head-worn display. We conducted a feasibility study under two different visual background conditions, namely dynamic background (TV) and static background (Wall) conditions. This study revealed a low false positive rate (TV: 0%, Wall: 2.10%) for Verge-it and acceptable performance.

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 &amp, 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.

Eyesight monitoring systems are of particular interest to virtual technology research teams and concern mainly three key aspects: physiological, technical and functional. The first one is to solve the so-called conflict of vergence and accommodation. In contrast to typical gaming applications, e.g. vision therapy requires the ability to smoothly transfer attention between the points of near and far. The technical aspect is primarily the search for new measurement methods, which is particularly important in the case of mobile goggles with limited computing capabilities of the processor. The last aspect concerns the possibility of creating effective HMI (Human Machine Interface) solutions. Full Text: PDF References J. D. Bayliss et. al., "Lazy Eye Shooter: a Novel Game Therapy for Visual Recovery in Adult Amblyopia", 2012 IEEE International Games Innovation Conference CrossRef Y. L. Chen., L. Shi, J. W. L. Lewis, M. Wang, "Infrared Retinoscopy", Photonics 2014, 1, 303-322. CrossRef W. Fuhl, M. Tonsen, A. Bulling, and E. Kasneci, "Pupil detection for head-mounted eye tracking in the wild: an evaluation of the state of the art," Mach. Vis. Appl., vol. 27, no. 8, pp. 1275-1288, 2016 CrossRef N. Sarkar, D. Strathearn, G. Lee, M. Olfat, A. Rohani and R. R. Mansour, "A large angle, low voltage, small footprint micromirror for eye tracking and near-eye display applications", 2015 Transducers - 2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), Anchorage, AK, 2015, pp. 855-858, CrossRef

Experiences of visual imagery, the ability to see in the mind’s eye, occur in various situations. The Vividness of Visual Imagery Questionnaire (VVIQ) has been widely used to subjectively measure the vividness of visualizers based on its score. For objective measurements, studies show that functional Magnetic Resonance Imaging (fMRI) can be used to measure individual variabilities of the vividness of visual imagery. However, questions are remained on how the visualizers see the images spatially. This study proposes a method to measure the spatial distribution of gaze in 3-dimensional space of an object seen by a visualizer using a glass-typed 3D eye tracker. The eye tracker estimated gaze in 3D based on vergence eye movements. Thus, if the visualizer reports good visual imagery of a given image, the eye tracker will be able to estimate the location of the object in 3-dimensional space. The eye tracker is equipped with polarizing lenses to enable the visualizer to see the given stimuli in both virtual and real worlds. Here, a 3D television (3DTV) is used to present the stimuli virtually. Ten introductory students completed the VVIQ and divided into two groups: high and low vividness visualizers, based on total scores of the VVIQ. Experiment results show that 3D gaze fixations of subjects who reported good visual imagery were relatively distributed around the location of the given stimuli.

Most people can voluntarily control vergence eye movements. However, the interaction possibility of using vergence as an active input remain largely unexplored. We present a novel human-computer interaction technique which allows a user to control the depth position of an object based on voluntary vergence of the eyes. Our technique is similar to the mechanism for seeing the intended 3D image of an autostereogram, which requires cross-eyed or walleyed viewing. We invite the user to look at a visual target that is mounted on a linear motor, then consciously control the eye convergence to focus at a point in front of or behind the target. A camera is used to measure the eye convergence and control the motion of the linear motor dynamically based on the measured distance. Our technique can enhance existing eye-tracking methods by providing additional information in the depth dimension, and has great potential for hands-free interaction and assistive applications.

The vertical misalignment of corresponding features in the left and right eyes' images are known as vertical disparities. They can arise from misalignment of cameras during image capture, projectors during presentation or misalignment of the eyes. The typical response to vertical disparity is an adjustment in the posture of the eyes, called vertical vergence. The range of disparities which elicit vertical vergence movements is unknown. Furthermore, previous research has investigated vertical disparities applied to the whole visual field, possibly masking any differences between regions of the visual field that elicit vergence movements more effectively than others. We determined the maximum disparity that could elicit vergence movements using disparities applied to the full field. We also measured the range of vertical disparities that elicit vertical vergence eye movements at discrete locations in the visual field and found that they drove corrective vertical vergence movements. However, we found no systematic differences across locations in the visual field. and that vergence movements were larger for full screen than for discrete stimuli. Finally, we examined the relationship between vertical vergence and fusion, finding that vertical vergence movements are elicited by diplopic stimuli, consistent with research on horizontal vergence movements.

Research finds a relationship between the development of depth perception and ocular motion functions including smooth pursuit and ocular following response. Infants' reactions to looming stimuli also suggest sensitivity to optic flow information that specifies relative distance. With radial optic flow, an expanding flow field elicits involuntary convergent eye movements while a contracting one elicits involuntary divergent eye movements. This response suggests the visual system is interpreting the radial flow as a change in relative depth. We measured the oculomotor response to radial optic flow in infants aged two to five months. The stimulus comprised a radial optic flow pattern that expanded or contracted across eight 400 ms trials while eye position was monitored with a Tobii X120 eye tracker. A subset of infants also viewed trials of a static version of the stimulus. On average, most infants in each age group demonstrated convergence to the expanding pattern and divergence to the contracting one. Moreover, the difference in gain between the convergence and divergence eye movements was significant. The presence of correct-direction vergence eye movements in response to expansion and contraction provides further evidence that infants are sensitive to information that specifies relative motion in depth.

A paucity of research exists to investigate whether the normal aging process influences the ability to adapt disparity vergence and phoria. Vergence eye movements and dissociated phoria were recorded from 49 healthy subjects (ages 20–70 years) using an objective eye movement tracking system. Four-degree vergence responses were modified using a double-step protocol. Dynamics of vergence were quantified via peak velocity. The phoria adaptation experiment measured the magnitude (net change in phoria level) and rate (magnitude divided by the time constant) of phoria adaption during 5 min of sustained fixation on a binocular target (40 cm/8.44° from midline). The magnitude of phoria adaptation decreased as a function of age (r =−0.33; p = 0.04). The ability to adapt vergence peak velocity and the rate of phoria adaptation showed no significant age-related influence (p > 0.05). The data suggest that the ability to modify the disparity vergence system and the rate of phoria adaptation are not dependent on age; whereas, the magnitude of phoria adaptation decreases as part of the normal adult aging process. These results have clinical and basic science implications because one should consider age when assessing the changes in the magnitude of phoria adaptation which can be abnormal in those with oculomotor dysfunctions.

The Wells–Hering's laws of perceived egocentric visual direction (EVD) assume that information about eye position includes equal contributions from both eyes. An implication of this assumption is that only versional eye movements should lead to a change in perceived EVD. Previously, we showed that a differential weighting of eye-position information occurs in some individuals during asymmetric vergence. To extend this finding, we determined here whether a differential weighting of eye-position information occurs also during symmetric vergence eye movements. Open-loop pointing responses to a bright target were obtained in five subjects to estimate the contribution of each eye's position information to perceived EVD during symmetric vergence demands that ranged from 6 prism diopters base in to 18 prism diopters base out. In all five subjects, the slopes of the lines fit to the pointing responses were in the direction that was predicted from an unequal weighting of eye-position information. We conclude that symmetric vergence movements can result in a change in perceived visual direction, contrary to an assumption of the Wells–Hering's laws.

Introduction The purpose was to investigate the effect of vergence reeducation on postural control, in subjects with isolated vergence disorders. Material and methods We studied the dynamics of vergence in 19 subjects (20–44 years old) using video-oculography (Eye See Cam). On the basis of orthoptic and symptomatology assessments, ten of the subjects were diagnosed for vergence disorders then vergence eye movements were reeducated with the REMOBI method (US8851669, 5 weekly sessions lasting for 35 min). Postural control was measured before and after reeducation, postural recording was done in upright stance (Dynaport), with both eyes closed or open and looking a visual target located at 2 m distance. Results After reeducation with REMOBI, the visual symptomatology faded away and the stereoacuity improved at least for some subjects; the vergence latency decreased significantly and the vergence accuracy increased significantly. In terms of posture, the Mean Power Frequency (MPF) of the body sway decreased significantly in both eyes open and eyes closed conditions. Considering all subjects together (i.e. healthy subjects and subjects with vergence disorders before the reeducation), the antero-posterior body sway (Root Mean Square A/P) was positively correlated with the visual symptomatology: the higher the visual symptomatology, the higher was the body sway. Conclusion The results bring evidence for synergy between the quality of vergence and the quality of postural control. They open a new research line that bridges the gap between neuroscience, ophthalmology-orthoptics and posturology.

We studied human short-latency vergence eye movements to a novel stimulus that produces interocular velocity differences without a changing disparity signal. Sinusoidal luminance gratings moved in opposite directions (left vs. right; up vs. down) in the two eyes. The grating seen by each eye underwent ¼-wavelength shifts with each image update. This arrangement eliminated changing disparity cues, since the phase difference between the eyes alternated between 0° and 180°. We nevertheless observed robust short-latency vergence responses (VRs), whose sign was consistent with the interocular velocity differences (IOVDs), indicating that the IOVD cue in isolation can evoke short-latency VRs. The IOVD cue was effective only when the images seen by the two eyes overlapped in space. We observed equally robust VRs for opposite horizontal motions (left in one eye, right in the other) and opposite vertical motions (up in one eye, down in the other). Whereas the former are naturally generated by objects moving in depth, the latter are not part of our normal experience. To our knowledge, this is the first demonstration of a behavioral consequence of vertical IOVD. This may reflect the fact that some neurons in area MT are sensitive to these motion signals (Czuba, Huk, Cormack, & Kohn, 2014). VRs were the strongest for spatial frequencies in the range of 0.35-1 c/°, much higher than the optimal spatial frequencies for evoking ocular-following responses observed during frontoparallel motion. This suggests that the two motion signals are detected by different neuronal populations. We also produced IOVD using moving uncorrelated one-dimensional white-noise stimuli. In this case the most effective stimuli have low speed, as predicted if the drive originates in neurons tuned to high spatial frequencies (Sheliga, Quaia, FitzGibbon, & Cumming, 2016).

The problem of triggering input accurately (with a small temporal offset) and precisely (with high repeatability) at a specific point in time has so far been largely ignored in gaze interaction research. We explore voluntary eye convergences as a novel interaction technique for precise and accurate timing of gaze input and a solution to the 'Midas touch' problem, i.e. the accidental triggering of input when looking at an interface. We introduce a novel clock paradigm to study input timing and demonstrate that voluntary convergences are significantly more accurate and precise than common gaze dwelling. Our findings suggest that voluntary convergences are well-suited for applications in which timing of user input is important, thereby complementing existing gaze techniques that focus on speed and spatial precision.

Visual attention is an important aspect of everyday life, which can be incorporated in the assessment of many diagnoses. Another important characteristic of visual attention is that it can be improved via therapeutic interventions. Fifteen subjects with normal binocular vision were presented with visual distractor stimuli at various spatial locations while initiating disparity vergence eye movements (inward or outward rotation of eyes) within a haploscope system. First, a stationary distractor stimulus was presented in either the far, middle, or near visual spaces while the subjects were instructed to follow a target stimulus that was either stationary, converging (moving toward subject), or diverging (moving away from subject). For the second experiment, a dynamic distractor stimulus within the far, middle, or near visual space that was converging or diverging was presented while the target stimulus was also converging or diverging. The subjects were instructed to visually follow the target stimulus and ignore the distractor stimulus. The vergence responses had a final vergence angle between the target and distractor stimuli which has been termed a center of gravity (CoG) effect. Statistically significant differences were observed between the convergence peak velocities (p < 0.001) and response amplitudes (p < 0.001) comparing responses without distractors to responses with the presence of a vergence distractor. The results support that vergence eye movements are influenced by visual distractors, which is similar to how distractors influence saccadic eye movements. The influence of visual distractors within vergence eye movements may be useful to assess binocular dysfunction and visual distraction which are common post brain injury.