Convergence Eye Movements Research Articles

Spinal Efference Copy Signaling and Gaze Stabilization during Locomotion in JuvenileXenopusFrogs

In swimming Xenopus laevis tadpoles, gaze stabilization is achieved by efference copies of spinal locomotory CPG output that produce rhythmic extraocular motor activity appropriate for minimizing motion-derived visual disturbances. During metamorphosis, Xenopus switches its locomotory mechanism from larval tail-based undulatory movements to bilaterally synchronous hindlimb kick propulsion in the adult. The change in locomotory mode leads to body motion dynamics that no longer require conjugate left-right eye rotations for effective retinal image stabilization. Using in vivo kinematic analyses, in vitro electrophysiological recordings and specific CNS lesions, we have investigated spino-extraocular motor coupling in the juvenile frog and the underlying neural pathways to understand how gaze control processes are altered in accordance with the animal's change in body plan and locomotor strategy. Recordings of extraocular and limb motor nerves during spontaneous "fictive" swimming in isolated CNS preparations revealed that there is indeed a corresponding change in spinal efference copy control of extraocular motor output. In contrast to fictive larval swimming where alternating bursts occur in bilateral antagonistic horizontal extraocular nerves, during adult fictive limb-kicking, these motor nerves are synchronously active in accordance with the production of convergent eye movements during the linear head accelerations resulting from forward propulsion. Correspondingly, the neural pathways mediating spino-extraocular coupling have switched from contralateral to strictly ipsilateral ascending influences that ensure a coactivation of bilateral extraocular motoneurons with synchronous left-right limb extensions. Thus, adaptive developmental plasticity during metamorphosis enables spinal CPG-driven extraocular motor activity to match the changing requirements for eye movement control during self-motion.

Prey Capture Behavior Evoked by Simple Visual Stimuli in Larval Zebrafish

Understanding how the nervous system recognizes salient stimuli in the environment and selects and executes the appropriate behavioral responses is a fundamental question in systems neuroscience. To facilitate the neuroethological study of visually guided behavior in larval zebrafish, we developed “virtual reality” assays in which precisely controlled visual cues can be presented to larvae whilst their behavior is automatically monitored using machine vision algorithms. Freely swimming larvae responded to moving stimuli in a size-dependent manner: they directed multiple low amplitude orienting turns (∼20°) toward small moving spots (1°) but reacted to larger spots (10°) with high-amplitude aversive turns (∼60°). The tracking of small spots led us to examine how larvae respond to prey during hunting routines. By analyzing movie sequences of larvae hunting paramecia, we discovered that all prey capture routines commence with eye convergence and larvae maintain their eyes in a highly converged position for the duration of the prey-tracking and capture swim phases. We adapted our virtual reality assay to deliver artificial visual cues to partially restrained larvae and found that small moving spots evoked convergent eye movements and J-turns of the tail, which are defining features of natural hunting. We propose that eye convergence represents the engagement of a predatory mode of behavior in larval fish and serves to increase the region of binocular visual space to enable stereoscopic targeting of prey.

The Processing of Three-Dimensional Shape from Disparity in the Human Brain

Three-dimensional (3D) shape is important for the visual control of grasping and manipulation and for object recognition. Although there has been some progress in our understanding of how 3D shape is extracted from motion and other monocular cues, little is known of how the human brain extracts 3D shape from disparity, commonly regarded as the strongest depth cue. Previous fMRI studies in the awake monkey have established that the interaction between stereo (present or absent) and the order of disparity (zero or second order) constitutes the MR signature of regions housing second-order disparity-selective neurons (Janssen et al., 2000; Srivastava et al., 2006; Durand et al., 2007; Joly et al., 2007). Testing the interaction between stereo and order of disparity in a large cohort of human subjects, revealed the involvement of five IPS regions (VIPS/V7*, POIPS, DIPSM, DIPSA, and phAIP), as well as V3 and the V3A complex in occipital cortex, the posterior inferior temporal gyrus (ITG), and ventral premotor cortex (vPrCS) in the extraction and processing of 3D shape from stereo. Control experiments ruled out attention and convergence eye movements as confounding factors. Many of these regions, DIPSM, DIPSA, phAIP, and probably posterior ITG and ventral premotor cortex, correspond to monkey regions with similar functionality, whereas the evolutionarily new or modified regions are located in occipital (the V3A complex) and occipitoparietal cortex (VIPS/V7* and POIPS). Interestingly, activity in these occipital regions correlates with the depth amplitude perceived by the subjects in the 3D surfaces used as stimuli in these fMRI experiments.

Visual screening of incercerated juvenile delinquents: a study of boys and girls remand homes, lagos state.

Visual characteristics of fifty (36 males and 14 females) incarcerated juvenile delinquents with forty six (consisting of 34 males and 12 females) incarcerated non delinquents in the defined population were compared using the New York State Optometric Association vision screening battery (NYSOA) and the minimum school vision screening programme. A chi-square test analysis revealed significantly higher frequencies for phoria, hyperopia, pursuit and saccadic eye movement subtests in the juvenile delinquent population as compared to the control group. Further analysis revealed significantly higher frequencies for convergence, phoria, hyperopia, pursuit and saccadic eye movement subtest (P Keywords : Visual acuity, Visual status, Visual skills, Stereo-acuity Annals of Biomedical Science Vol. 2 (1) 2003: pp. 11-19

Involvement of the Cerebellar Dorsal Vermis in Vergence Eye Movements in Monkeys

Frontal-eyed primates use both smooth pursuit in frontoparallel planes (frontal pursuit) and pursuit-in-depth (vergence pursuit) to track objects moving slowly in 3-dimensional (3D) space. To understand how 3D-pursuit signals represented in frontal eye fields are processed further by downstream pathways, monkeys were trained to pursue a spot moving in 3D virtual space. We characterized pursuit signals in Purkinje (P) cells in the cerebellar dorsal vermis and their discharge during vergence pursuit. In 41% of pursuit P-cells, 3D-pursuit signals were observed. However, the majority of vermal-pursuit P-cells (59%) discharged either for vergence pursuit (43%) or for frontal pursuit (16%). Moreover, the majority (74%) of vergence-related P-cells carried convergence signals, displaying both vergence eye position and velocity sensitivity during sinusoidal and step vergence eye movements. Preferred frontal-pursuit directions of vergence + frontal-pursuit P-cells were distributed in all directions. Most pursuit P-cells (73%) discharged before the onset of vergence eye movements; the median lead time was 16 ms. Muscimol infusion into the sites where convergence P-cells were recorded resulted in a reduction of peak convergence eye velocity, of initial convergence eye acceleration, and of frontal-pursuit eye velocity. These results suggest involvement of the dorsal vermis in conversion of 3D-pursuit signals and in convergence eye movements.

Properties of the anticipatory convergence eye movement

Properties of the anticipatory convergence eye movement

Binocular coordination of saccades in children with vertigo: Dependency on the vergence state

The present study examines the quality of binocular coordination of saccades at far and near distance in 15 children with symptoms of vertigo headache and equilibrium disorders; these children show normal vestibular function but abnormal convergence eye movements (e.g., long time preparation, slow execution and poor accuracy, see Bucci, Kapoula, Yang, Bremond-Gignac, & Wiener-Vacher, 2004a, 2004b). The results show normal binocular saccade coordination at far distance, but large abnormal disconjugacy for saccades at near distance. During combined saccade–vergence movements (studied in six of these children), convergence remains abnormally slow. This supports the interpretation according to which poor binocular yoking of the saccades is linked to the reduced ability to produce fast convergence during the saccade; a learning mechanism based on rapid vergence would help to reduce the abducting–adducting asymmetry of the saccades. An alternative interpretation would be reduced learning ability for monocular adjustment of the saccade signals.

Visual cortical contribution to open-loop and feed-back control of convergence eye movements in the cat

Open-loop and closed loop controls in convergence eye movement have been reported by human psycho-physical studies. To investigate the visual cortical involvement in open-loop convergence eye movement, we trained a cat to elicit anticipatory convergence (convergence eye movement before the onset of target movement) by using an approaching visual target with a preceding alarm signal. After 1–2 weeks of training, anticipatory convergence was observed in more than half of the trials in seven cats. The frequency of occurrence of anticipatory convergence was significantly decreased after electrocoagulation in the convergence-related region of the lateral suprasylvian (LS) area, an extrastriate visual cortex of the cat. On the other hand, the localized injection of Muscimol, a GABA-A agonist, reduced visually evoked convergence, but caused no significant effects to anticipatory convergence. These differential results suggest that the LS plays a role in both open-loop and feed-back control of convergence eye movement, and a GABA-A sensitive subregion is involved in the feed-back control of convergence eye movement.

Short‐Latency Disparity Vergence in Humans: Evidence for Early Spatial Filtering

Our study was concerned with the disparity detectors underlying the initial disparity vergence responses (DVRs) that are elicited at ultrashort latencies by binocular disparities applied to large images. DVRs were elicited in humans by applying horizontal disparity to vertical square-wave gratings lacking the fundamental (termed here, the "missing fundamental"). In the frequency domain, a pure square wave is composed of odd harmonics--first, third, fifth, seventh, etc.--such that the third, fifth, seventh, etc., have amplitudes that are one-third, one-fifth, one-seventh, etc., that of the first, and the missing fundamental lacks the first harmonic. The patterns seen by the two eyes have a phase difference of one-quarter wavelength, so the disparity of the features and 4n + 1 harmonics (where n = integer) has one sign (crossed or uncrossed), whereas the 4n - 1 harmonics--including the strongest Fourier component (the third harmonic)--has the opposite sign (uncrossed or crossed): spatial aliasing. The earliest DVRs, recorded with the search-coil technique, had minimum latencies of 70 to 80 ms and were generally in the direction of the third harmonic, that is, uncrossed disparities resulted in convergent eye movements. In other experiments on the DVRs, one eye saw a missing fundamental and the other saw a pure sine wave with the contrast and wavelength of the third harmonic but differing in phase by one-quarter wavelength. This resulted in short-latency vergence in accordance with matching of the third harmonic. These data all indicate the importance of the Fourier components, consistent with early spatial filtering prior to binocular matching.

Latency of adaptive vergence eye movements induced by vergence-vestibular interaction training in monkeys.

Clear vision of objects that move in depth toward or away from an observer requires vergence eye movements. The vergence system must interact with the vestibular system to maintain the object images on the foveae of both eyes during head movement. Previous studies have shown that training with sinusoidal vergence-vestibular interaction improves the frequency response of vergence eye movements during pitch rotation: vergence eye velocity gains increase and phase-lags decrease. To further understand the changes in eye movement responses in this adaptation, we examined latencies of vergence eye movements before and after vergence-vestibular training. Two head-stabilized Japanese monkeys were rewarded for tracking a target spot moving in depth that required vergence eye movements of 10 degrees/s. This target motion was synchronized with pitch rotation at 20 degrees/s. Both target and chair moved in a trapezoidal waveform interspersed with random inter-trial intervals. Before training, pitch rotation in complete darkness without a target did not induce vergence eye movements. Mean latencies of convergence and divergence eye movements induced by vergence target motion alone were 182 and 169 ms, respectively. After training, mean latencies of convergence and divergence eye movements to a target synchronized with pitch rotation shortened to 65 and 53 ms, and vergence eye velocity gains (relative to vergence target velocity) at the normal latencies were 0.68 and 1.53, respectively. Pitch rotation alone without a target induced vergence eye movements with similar latencies after training. These results indicate that vestibular information can be used effectively to initiate vergence eye movements following vergence-vestibular training.

Transcranial magnetic stimulation of the posterior parietal cortex delays the latency of both isolated and combined vergence–saccade movements in humans

To explore the 3D visual environment most frequently we make combined saccade–vergence eye movements. We studied the effect of transcranial magnetic stimulation (TMS) of the right posterior parietal cortex (rPPC) on such combined eye movements versus isolated saccade and vergence. In the main experiment, TMS was applied on the rPPC 80, 90 or 100 ms after target onset. In a control experiment, TMS was applied over the primary motor cortex at 90 ms after the target presentation. TMS trials were compared with no-TMS trials. TMS of the motor cortex had no effect at all on eye movements. TMS of the rPPC had no effect on the accuracy of eye movements, but it caused a latency increase: the increase was similar for the two components of the combined saccade–vergence movements, and it did not alter the naturally existing tight relationship of latency between the two components. Furthermore, the amount of latency prolongation was similar to that of isolated vergence, and of saccades in either direction (ipsilateral or contralateral relative to the stimulated site). Latency prolongation was time-specific but in a different way for different types of eye movements: for combined and convergence eye movements, the critical time window was −130 ms or more prior to the onset of eye movement, while for saccades and divergence TMS was disruptive later, −110 ms or more prior to the onset of eye movements. The latency increase is attributed to the interference by the TMS with the fixation disengagement process, for which the rPPC is believed to be instrumental. These results suggest that fixation disengagement occurs earlier for convergence and combined eye movements than for saccades and divergence.

Maldevelopment of convergence eye movements in macaque monkeys with small- and large-angle infantile esotropia.

To describe symmetric convergence eye movements evoked by disparity and/or accommodative cues in esotropic macaque monkeys, with the goal of determining whether these animals have the vergence deficits found in humans with esotropia. Physical far and near targets were used to evoke large (approximately 8 degrees) symmetric convergence eye movements in four adult macaque monkeys (two with strabismus, two normal), using positive-feedback rewards. One strabismic monkey had infantile-onset, small-angle esotropia (small-eso approximately 2 degrees) induced by alternating occlusion from birth to age 9 months. The other strabismic monkey had naturally occurring, large-angle (approximately 25 degrees) infantile-onset esotropia (large-eso). Visual acuity was normal in each eye as measured by spatial sweep visually evoked potentials (VEPs). Eye movements were recorded using magnetic search coils. When viewing binocularly, both normal monkeys exhibited accurate, stereotyped symmetric convergence movements that achieved 87% to 96% of the required change in vergence angle by the end of the initial movement. In contrast, the small-eso monkey's convergence response when viewing binocularly was variable, strikingly asymmetric, usually accompanied by a disjunctive saccade, and subnormal, achieving only 56% of required vergence. The convergence response of the large-eso monkey was also asymmetric and weak, achieving 18% of the required vergence and employing conjugate saccades to refixate the near target. Monocular viewing (i.e., accommodative vergence) caused substantial reductions in both convergence amplitudes and velocities in the normal monkeys, but had a minor effect on the vergence behavior of the strabismic animals. Monkeys with small- and large-angle infantile esotropia have striking maldevelopments of binocular (disparity-driven) convergence and use accommodative vergence and saccades to refixate near targets. Their vergence behavior resembles that in esotropic humans. The maldevelopment may be explained in large part by the paucity of binocular connections recently described in the visual cortex of esotropic macaques.

A study of visual fatigue and visual comfort for 3D HDTV/HDTV images

We compared visual fatigue caused by HDTV and stereoscopic HDTV at the viewing distance of 4.5 m. We measured the degree of visual fatigue using a subjective test method and compared it to an objective measure, namely the change in accommodation before and after viewing images. We also detected visual discomfort image scenes from the best program using the single stimulus continuous quality method. As a result, the mechanism between convergence eye movement and the accommodation function in the depth of focus in addition to conflict of convergence eye movement and accommodation function appears to affect visual fatigue. From the examination between the results of single stimulus quality evaluation and the feature characteristics of test stereoscopic images, we found that a local low subjective evaluation appeared for both high degree of parallax and amount of motion in the test stereoscopic images. But motion components were very small, the subjective evaluation value was rarely very low.

Dynamic Asymmetries in Convergence Eye Movements Under Natural Viewing Conditions

Purpose: To clarify differences in the dynamics of convergence eye movements in response to symmetrical stimuli between the dominant eye and the nondominant eye under natural viewing conditions. Methods: This study was conducted in 11 normal volunteers (age range, 22–30 years). The subject was seated on a chair, and the head was fixed using a bite-block. The dominant eye was determined with the “hole-in-the-card” test. Horizontal positions of the eyes were recorded using an infrared reflection device. Recordings of right eye movements were subtracted from left eye movements to obtain the vergence response. The fixation target was moved toward the center of both eyes from 50 to 20 cm in front of the face at a constant velocity in five steps (20, 30, 40, 50, and 60 cm/s). The target was moved by a pulse motor controlled by a microcomputer. The dynamic properties of each eye movement and the vergence components were analyzed. Results: At velocities ≤40 cm/s, convergence responses consisted of two components: the fusion-initiating component and the fusion-sustaining component. The fusion-initiating component drove the initial faster dynamic portion of the response, and the fusion-sustaining component maintained the latter slower dynamic portion of the response. The mean peak velocity of the fusion-initiating component was significantly greater in the dominant eye than in the nondominant eye. The mean peak latency of the catch-up component was significantly shorter in the dominant eye than in the nondominant eye. Conclusions: The present study indicated that the trajectory of convergence eye movement under natural viewing conditions consists of two components, the fusion-initiating component and the fusion-sustaining component, and that the convergence response to symmetric stimuli was asymmetric between the dominant eye and the nondominant eye during the fusion-initiating phase. The neural control system of convergence eye movements preferentially drives the dominant eye during the fusion-initiating phase of the response.

The properties of convergence eye movements evoked from the rostral and caudal lateral suprasylvian cortex in the cat.

Convergence eye movements were evoked in the lateral suprasylvian cortex (LS cortex) in the cat. Three effective regions were found: the rostral and caudal parts of the postero-medial LS cortex (the PMLS) and the rostral part of the postero-lateral LS cortex (the PLLS). These three areas represent the central and paracentral visual fields in the published retinotopic map (Palmer et al., 1978). Convergence eye movements evoked from the caudal PMLS were divided into two groups based on their latencies; the short-latency components (SLC) and long-latency components (LLC). The SLC and the LLC had differences in their symmetry of right and left eye movements during vergence eye movement. The SLC had symmetric right and left eye components and the LLC had dominant contralateral eye components. In the rostral PMLS, latencies of evoked convergence eye movement were comparable to those of the caudal PMLS, but they did not divided into two groups. Convergence eye movements evoked from the PLLS had longer latencies than those from the PMLS and asymmetric right and left eye components. It is suggested that different subregions in the LS cortex contribute to the control of convergence eye movement, playing different roles.

The influence of repetitive eye movements on vergence performance

We measured the peak velocity of convergence eye movement responses in four normal subjects before and after a large number of either repetitive vergence or repetitive saccadic eye movements. A 20% decrease in the mean value of peak velocity was observed in vergence responses after 100 repetitive step vergence eye movements. However, 100 cycles of slow sinusoidal vergence tracking did not induce any notable change in vergence dynamics. Five hundred repetitive saccadic eye movements also caused an approximately 20% decrease in peak velocity. The reduction in peak velocity was related to the number of repetitions for both vergence and saccadic fatiguing stimuli. The frequency of occurrence of double-vergences was also used as an index to monitor the influence of repetitive eye movements on convergence performance. Results showed that repetitive step convergence movements could double, or even triple, the frequency of the occurrence of double-vergence responses, while slow sinusoidal vergence tracking or repetitive saccades had no influence on the frequency of response doubles.

Multifocal planes head-mounted displays

Stereoscopic head-mounted displays (HMD's) provide an effective capability to create dynamic virtual environments. For a user of such environments, virtual objects would be displayed ideally at the appropriate distances, and natural concordant accommodation and convergence would be provided. Under such image display conditions, the user perceives these objects as if they were objects in a real environment. Current HMD technology requires convergent eye movements. However, it is currently limited by fixed visual accommodation, which is inconsistent with real-world vision. A prototype multiplanar volumetric projection display based on a stack of laminated planes was built for medical visualization as discussed in a paper presented at a 1999 Advanced Research Projects Agency workshop (Sullivan, Advanced Research Projects Agency, Arlington, Va., 1999). We show how such technology can be engineered to create a set of virtual planes appropriately configured in visual space to suppress conflicts of convergence and accommodation in HMD's. Although some scanning mechanism could be employed to create a set of desirable planes from a two-dimensional conventional display, multiplanar technology accomplishes such function with no moving parts. Based on optical principles and human vision, we present a comprehensive investigation of the engineering specification of multiplanar technology for integration in HMD's. Using selected human visual acuity and stereoacuity criteria, we show that the display requires at most 27 equally spaced planes, which is within the capability of current research and development display devices, located within a maximal 26-mm-wide stack. We further show that the necessary in-plane resolution is of the order of 5 microm.

Effects of localized lesions in the lateral suprasylvian cortex on convergence eye movement in cats

We evaluated the effects of electrolytic lesions in the extrastriate cortical area on the amplitudes and velocities of vergence eye movements in six alert cats that were trained to track a target moving in depth. Bilateral or unilateral lesions in the lateral suprasylvian (LS) cortex reduced the amplitudes and velocities of vergence eye movements, but the positive correlation between them was maintained. Furthermore, unilateral lesions changed the symmetry of eye movements. Movements of the left eye were decreased by lesions in the right LS cortex, resulting in asymmetric vergence eye movement with right eye predominance, and vice versa. These results support the hypothesis that the LS cortex plays an essential role in controlling vergence eye movement.

Dynamic details of disparity convergence eye movements.

Classically, the primary tool for quantifying the dynamics of vergence and other eye movements has been the main sequence. The main sequence is a plot of peak velocity versus response amplitude and is particularly useful for comparing the dynamics of a large number of eye movements over a range of response amplitudes. However, the main sequence represents only the equivalent first-order behavior of a response and does not describe its dynamics in detail. Since the main sequence is based on only two points on the dynamic trajectory, it is sensitive to measurement artifacts and noise. A new methodology is presented which quantifies the equivalent second-order dynamics of eye movements using a larger region of the transient response. These new indexes were applied to vergence eye movements and were found to differentiate between subtle, but important differences in movement dynamics.

Basic Experiments for Evaluating Peculiar Ocular Characteristics Caused by Artificial Binocular Vision

By using Eye-Sensing Head Mounted Display (ES-HMD), basic laboratory experiments were conducted to evaluate convergent eye movement and pupil size under some specific visual conditions induced by artificial binocular vision; one experimental condition was that asymmetric luminous intensity for both eyes was illuminated. The result shows that each pupil size of both eyes in asymmetric condition is different from in symmetric condition, even if each eye is illuminated by the same luminous intensity for the both conditions. Since the experimental condition would never usually happen in real world, longtime exposure to light in asymmetric luminous condition may lead to visual fatigue. The other experimental condition was binocular vision generated by binocular parallax. It was found that (i) some subjects, who are called vergence normal, can adjust convergence according to the moving target with binocular parallax, but the other called vergence anomaly cannot, and (ii) pupil size in a vergence normal changes with the vergent eye movement induced by binocular parallax. These results show that a vergence anomaly, who is also called stereoanomaly, can be easily detected by using simple test image and observing vergence eye movement or pupil size. The obtained relation between pupil size and binocular parallax is also a new experimental proof of influence of vergent eye movement to the change of pupil size.