Saccadic Eye Research Articles

2126 Optimizing a technique for visualizing retinal and choroidal blood flow noninvasively

OBJECTIVES/SPECIFIC AIMS: Diabetic retinopathy is an increasingly prevalent disease, difficult to screen for across the globe. We have developed and began optimizing an innovative technique to visualize and quantify retinal blood flow, to elucidate the role of the choroid in retinal pathologies such as diabetic retinopathy or choroidopathy. METHODS/STUDY POPULATION: Preliminary retinal was obtained from a surgical retina video library (Truvision, Goleta, CA, USA). Videos of different organs were recorded while vessels were occluded via a blood pressure cuff, using consumer-grade digital video cameras (NEX-5T, a7sii; Sony, New York, NY, USA). All other retinal videos were taken using a fundus camera (50×; Topcon, Oxland, NJ, USA) modified to support the above digital video cameras. All videos were processed using experimental software (MATLAB, Mathworks, Natick, MA, USA). RESULTS/ANTICIPATED RESULTS: Video imaging of the retina was optimized for lighting conditions and software requirements. Parameters were defined for the software imaging pipeline, such as frequency range of interest, sampling rate, and noise minimization. Software was developed to stabilize frames, accounting for eye saccades. Use of a biosensor enabled accurate measurement of pulse waveform, increasing signal-to-noise ratio. The optimal light requirements were determined such that adequate exposure of the retina is reproducible yet still comfortable for use in human subjects. DISCUSSION/SIGNIFICANCE OF IMPACT: This novel technique allows for an inexpensive, noninvasive, and reproducible ocular blood flow imaging platform. By optimizing this technique, we can proceed with our future plans for a pilot study to compare our imaging technique with the current standard, paving the way for future clinical studies.

Visuospatial Working Memory as a Fundamental Component of the Eye Movement System

Humans make frequent movements of the eyes (saccades) to explore the visual environment. Here, we argue that visuospatial working memory (VSWM) is a fundamental component of the eye movement system. Memory representations in VSWM are functionally integrated at all stages of orienting: (a) selection of the target; (b) maintenance of visual features across the saccade; (c) the computation of object correspondence after the saccade, supporting the experience of perceptual continuity; and (d) the correction of gaze when the eyes fail to land on the intended object. VSWM is finely tuned to meet the challenges of active vision.

A Comparison of Change Blindness in Real-World and On-Screen Viewing of Museum Artefacts

Change blindness is a phenomenon of visual perception that occurs when a stimulus undergoes a change without this being noticed by its observer. To date, the effect has been produced by changing images displayed on screen as well as changing people and objects in an individual’s environment. In this experiment, we combine these two approaches to directly compare the levels of change blindness produced in real-world vs. on-screen viewing of museum artefacts. In the real-world viewing condition, one group of participants viewed a series of pairs of similar but slightly different artefacts across eye saccades, while in the on-screen viewing condition, a second group of participants viewed the same artefacts across camera pans on video captured from a head-mounted camera worn by the first set of participants. We present three main findings. First, that change blindness does occur in a museum setting when similar ancient artefacts are viewed briefly one after another in both real-world and on-screen viewing conditions. We discuss this finding in relation to the notion that visual perceptual performance may be enhanced within museums. Second, we found that there was no statistically significant difference between the mean levels of change blindness produced in real-world and on-screen viewing conditions (real-world 42.62%, on-screen 47.35%, X2 = 1.626, p > 0.05 1 d.f.). We discuss possible implications of these results for understanding change blindness, such as the role of binocular vs. monocular vision and that of head and eye movements, as well as reflecting on the evolution of change detection systems, and the impact of the experimental design itself on our results. Third, we combined the data from both viewing conditions to identify groups of artefacts that were independently associated with high and low levels of change blindness, and show that change detection rates were influenced mainly by bottom-up factors, including the visible area and contrast of changes. Finally, we discuss the limitations of this experiment and look to future directions for research into museum perception, change blindness, real-world and on-screen comparisons, and the role of bottom-up and top-down factors in the perception of change.

An ocular biomechanic model for dynamic simulation of different eye movements

Simulating and analysing eye movement is useful for assessing visual system contribution to discomfort with respect to body movements, especially in virtual environments where simulation sickness might occur. It can also be used in the design of eye prosthesis or humanoid robot eye. In this paper, we present two biomechanic ocular models that are easily integrated into the available musculoskeletal models. The model was previously used to simulate eye-head coordination. The models are used to simulate and analyse eye movements. The proposed models are based on physiological and kinematic properties of the human eye. They incorporate an eye-globe, orbital suspension tissues and six muscles with their connective tissues (pulleys). Pulleys were incorporated in rectus and inferior oblique muscles. The two proposed models are the passive pulleys and the active pulleys models. Dynamic simulations of different eye movements, including fixation, saccade and smooth pursuit, are performed to validate both models. The resultant force-length curves of the models were similar to the experimental data. The simulation results show that the proposed models are suitable to generate eye movement simulations with results comparable to other musculoskeletal models. The maximum kinematic root mean square error (RMSE) is 5.68° and 4.35° for the passive and active pulley models, respectively. The analysis of the muscle forces showed realistic muscle activation with increased muscle synergy in the active pulley model.

Execution of saccadic eye movements affects speed perception

Due to the foveal organization of our visual system we have to constantly move our eyes to gain precise information about our environment. Doing so massively alters the retinal input. This is problematic for the perception of moving objects, because physical motion and retinal motion become decoupled and the brain has to discount the eye movements to recover the speed of moving objects. Two different types of eye movements, pursuit and saccades, are combined for tracking. We investigated how the way we track moving targets can affect the perceived target speed. We found that the execution of corrective saccades during pursuit initiation modifies how fast the target is perceived compared with pure pursuit. When participants executed a forward (catch-up) saccade they perceived the target to be moving faster. When they executed a backward saccade they perceived the target to be moving more slowly. Variations in pursuit velocity without corrective saccades did not affect perceptual judgments. We present a model for these effects, assuming that the eye velocity signal for small corrective saccades gets integrated with the retinal velocity signal during pursuit. In our model, the execution of corrective saccades modulates the integration of these two signals by giving less weight to the retinal information around the time of corrective saccades.

Eye-Head Coordination in 31 Space Shuttle Astronauts during Visual Target Acquisition

Between 1989 and 1995, NASA evaluated how increases in flight duration of up to 17 days affected the health and performance of Space Shuttle astronauts. Thirty-one Space Shuttle pilots participating in 17 space missions were tested at 3 different times before flight and 3 different times after flight, starting within a few hours of return to Earth. The astronauts moved their head and eyes as quickly as possible from the central fixation point to a specified target located 20°, 30°, or 60° off center. Eye movements were measured with electro-oculography (EOG). Head movements were measured with a triaxial rate sensor system mounted on a headband. The mean time to visually acquire the targets immediately after landing was 7–10% (30–34 ms) slower than mean preflight values, but results returned to baseline after 48 hours. This increase in gaze latency was due to a decrease in velocity and amplitude of both the eye saccade and head movement toward the target. Results were similar after all space missions, regardless of length.

The Role of Predictability in Saccadic Eye Responses in the Suppression Head Impulse Test of Horizontal Semicircular Canal Function.

In the suppression head impulse paradigm (SHIMP) vHIT protocol, the participant is instructed to follow with his gaze a mobile target generated by a laser placed on the participant's head. Recent studies have reported that the refixation saccade latencies are in relation with the time evolution of the vestibular dysfunction in both (standard and SHIMP) procedures. We hypothesized that some central mechanisms like head impulse prediction could be one of the causes for the differences in the saccadic eye responses. A prospective cohort non-randomized study was designed. For the SHIMP protocol, recorded with the ICS Impulse ver. 4.0® (Otometrics A/S, Taastrup, Denmark) vHIT device, three different algorithms were performed: "predictable," "less predictable," and "unpredictable" depending on the target's predictability. A mathematical method was developed to analyze the SHIMP responses. The method was implemented as an additional tool to the MATLAB open source script for the extended analysis of the vHIT responses named HITCal. In cohort 1, 52 participants were included in "predictable" SHIMP protocol. In cohort 2, 60 patients were included for the "less predictable" and 35 patients for the "unpredictable" SHIMP protocol. The participants made more early saccades when instructed to perform the "predictable" paradigm compared with the "less predictable" paradigm (p < 0.001). The less predictable protocol did not reveal any significant difference when compared with the unpredictable protocol (p = 0.189). For the latency of the first saccade, there was statistical difference between the "unpredictable" and "predictable" protocols (p < 0.001) and between the "less predictable" and "predictable" protocols (p < 0.001). Finally, we did not find any relationship between the horizontal vestibulo-ocular reflex (hVOR) gain and the latency of the saccades. We developed a specific method to analyze and detect early SHIMP saccades. Our findings offer evidence regarding the influence of predictability on the latency of the SHIMP saccadic responses, suggesting that early saccades are probably caused by a conditioned response of the participant. The lack of relationship between the hVOR gain and the latency of the saccades suggests that the predictive behavior that caused the early eye saccades are independent of the vestibular function.

P364 Female fragile X premutation carriers do exhibit subclinical neurological signs

Objective Premutation of fragile X mental retardation 1 gene is known to cause fragile X associated tremor ataxia syndrome in males at 50–60 years of age, and fragile X associated primary ovarian insufficiency (FXPOI) in females at around 40. Females rarely exhibit tremor/ataxia. The exact molecular pathomechanism of FXPOI is unknown. Our aim was to perform a systematic study on tremor, eye movements and neuropsychological performance in female Fragile X (FraX) premutation carriers. Methods We have examined 13 young female premutation carriers (mean age 38 years) with/without FXPOI. Tremor (resting, postural, intentional, kinetic) was recorded with an accelerometry-based test system. Electrooculography (EOG) system was used for qualitative and quantitative analysis of eye movements. Neuropsychological assessment was performed with a complex battery including Montreal Cognitive Assessment, Rey auditory verbal learning test, Rey Complex Figure Test, and Wisconsin Card Sorting Test. Results We could detect cerebellar tremor in only 1/13 case. Saccadic smooth pursuit eye movements and decreased velocity of the horizontal reflexive saccades were recorded in 6/11 females with valid EOG. Neuropsychology tests showed impaired verbal memory and visuo-spatial memory with preserved visuo-spatial perception. Tests showed neither impairments in the executive functions, nor decrease of general intelligence. Discussion Objective neurophysiological methods are needed to reveal neurological signs of female premutation carriers. Conclusions Female FraX premutation carriers might exhibit subclinical neurological signs at young age. Significance To best of our knowledge, this is the first quantitative study on eye movements of female FraX premutation carriers. Our study provides new insight into movement disorders of female premutation carriers.

Threat effects on human oculo-motor function

Neuro-anatomical evidence supports the potential for threat-related factors, such as fear, anxiety and vigilance, to influence brainstem motor nuclei controlling eye movements, as well as the vestibular nuclei. However, little is known about how threat influences human ocular responses, such as eye saccades (ES), smooth pursuit eye tracking (SP), and optokinetic nystagmus (OKN), and whether these responses can be facilitated above normal baseline levels with a natural source of threat. This study was designed to examine the effects of height-induced postural threat on the gain of ES, SP and OKN responses in humans. Twenty participants stood at two different surface heights while performing ES (ranging from 8° to 45° from center), SP (15, 20, 30°/s) and OKN (15, 30, 60°/s) responses in the horizontal plane. Height did not significantly increase the slope of the relationship between ES peak velocity and initial amplitude, or the gain of ES amplitude. In contrast height significantly increased SP and OKN gain. Significant correlations were found between changes in physiological arousal and OKN gain. Observations of changes with height in OKN and SP support neuro-anatomical evidence of threat-related mechanisms influencing both oculo-motor nuclei and vestibular reflex pathways. Although further study is warranted, the findings suggest that potential influences of fear, anxiety and arousal/alertness should be accounted for, or controlled, during clinical vestibular and oculo-motor testing.

Brain-computer interface combining eye saccade two-electrode EEG signals and voice cues to improve the maneuverability of wheelchair.

Brain-computer interfaces (BCIs) largely augment human capabilities by translating brain wave signals into feasible commands to operate external devices. However, many issues face the development of BCIs such as the low classification accuracy of brain signals and the tedious human-learning procedures. To solve these problems, we propose to use signals associated with eye saccades and blinks to control a BCI interface. By extracting existing physiological eye signals, the user does not need to adapt his/her brain waves to the device. Furthermore, using saccade signals to control an external device frees the limbs to perform other tasks. In this research, we use two electrodes placed on top of the left and right ears of thirteen participants. Then we use Independent Component Analysis (ICA) to extract meaningful EEG signals associated with eye movements. A sliding-window technique was implemented to collect relevant features. Finally, we classified the features as horizontal or blink eye movements using KNN and SVM. We were able to achieve a mean classification accuracy of about 97%. The two electrodes were then integrated with off-the-shelf earbuds to control a wheelchair. The earbuds can generate voice cues to indicate when to rotate the eyeballs to certain locations (i.e., left or right) or blink, so that the user can select directional commands to drive the wheelchair. In addition, through properly designing the contents of voice menus, we can generate as many commands as possible, even though we only have limited numbers of states of the identified eye saccade movements.

P‐141: Phantom Array Effect of LED Lighting

This paper studies the influence of the LED modulation frequency and eye saccade amplitude on the visibility of the phantom array effect. Results show that the phantom array effect becomes invisible at 3000 Hz. Besides, visibility thresholds at lower frequencies were not influenced by saccade amplitudes (20° and 40°).

Eye Movement Characteristics of Cooperation Degree during Image Completion Test in Psychiatric Impairment Assessment

To explore the difference of eye movement characteristics between uncooperative and cooperative subjects with mental disorder after cerebral trauma. Thirty-nine subjects which needed psychiatric impairment assessment were selected. According to the binomial forced-choice digit memory test （BFDMT）, all subjects were divided into cooperative and uncooperative groups. The subjects were asked to take the image completion test from Wechsler adult intelligence scale. Meanwhile, the data of eye movement track, fixation, saccade, pupil and blink were recorded by the track system of eye movement. There were significantly differences （P<0.05） in the data of saccade between cooperative （10 cases） and uncooperative groups （29 cases）. The frequency, time, amplitude, acceleration of saccadic in uncooperative group were significantly higher than cooperation group. The saccade latencies of cooperation group increased more than uncooperative group. There was a significant difference （P<0.05） in total discrete distance, average distance and total time of fixation between two groups, while the average duration time, number and frequency of fixation had no significantly difference （P>0.05） between two groups. And the blink frequency of cooperation group was higher than uncooperative group. Eye movement can be an objective index for the primary judgment of cooperation level.

Posterior Parietal Visual Dysfunction: An Explanatory Review

Dysfunction or injury of the posterior parietal lobes impairs 3D mapping of the visual scene and can… (1) Make body movement guided by vision inaccurate (optic ataxia). (2) Limit the number of items seen at a glance, due to simultanagnostic visual dysfunction. (3) Cause inability to move the eyes to a specified target (apraxia of gaze), despite intact pursuit and fast (saccadic) eye movements. (Perhaps because the target cannot be located.) When severe, these features comprise Balint syndrome, but when less marked, the term dorsal stream dysfunction has been used. Associated lower visual field impairment due to the superior optic radiations passing through the parietal lobes being affected as well, can cause the feet not to be seen during locomotion. While accompanying inability to see fast moving targets, or dyskinetopsia is not uncommon. In our experience, a wider inflight gap between the fingers and thumb of a hand reaching in the lower visual field than when reaching in the upper visual field, and disability locating where sounds are coming from, may also be evident. Central and peripheral visual functions can be diminished if the occipital lobes are affected as well, while recognition can be impaired by this and / or associated temporal lobe dysfunction. Those with accompanying intellectual impairment and four-limb cerebral palsy may ‘wake up’ and start to look around, even reaching out for a single object, when surrounded by a monochromatic tent that excludes extraneous visual and auditory distraction. In the authors’ experience, dorsal stream dysfunction is the commonest pattern of cerebral visual impairment seen in children and in many affected (often previously undiagnosed) adults. A series of case history data is presented to illustrate the origin, nature and heterogeneity of this condition, as well as its potential management.

Visual-vestibular processing deficits in mild traumatic brain injury.

The search for reliable and valid signs and symptoms of mild traumatic brain injury (mTBI), commonly synonymous with concussion, has lead to a growing body of evidence that individuals with long-lasting, unremitting impairments often experience visual and vestibular symptoms, such as dizziness, postural and gait disturbances. Investigate the role of visual-vestibular processing deficits following concussion. A number of clinically accepted vestibular, oculomotor, and balance assessments as well as a novel virtual reality (VR)-based balance assessment device were used to assess adults with post-acute concussion (n = 14) in comparison to a healthy age-matched cohort (n = 58). Significant between-group differences were found with the VR-based balance device (p = 0.001), with dynamic visual motion emerging as the most discriminating balance condition. The symptom reports collected after performing the oculomotor and vestibular tests: rapid alternating horizontal eye saccades, optokinetic stimulation, and gaze stabilization, were all sensitive to health status (p < 0.05), despite the absence of oculomotor abnormalities being observed, except for near-point convergence. The BESS, King-Devick, and Dynamic Visual Acuity tests did not detect between-group differences. Postural and visual-vestibular tasks most closely linked to spatial and self-motion perception had the greatest discriminatory outcomes. The current findings suggest that mesencephalic and parieto-occipital centers and pathways may be involved in concussion.

After Effects of Cerebellar Continuous Theta Burst Stimulation on Reflexive Saccades and Smooth Pursuit in Humans.

The use of cerebellar repetitive transcranial magnetic stimulation has been attempted for perturbing reflexive and voluntary eye movements, but discrepancies are seen between the results of distinct studies possibly due to the different stimulation sites, intensities, and paradigms. We describe the after effects of 20 and 40s continuous Theta Burst Stimulation (cTBS) as compared to sham stimulation, applied over the lateral cerebellar vermis and paravermis on Reflexive Saccades (RS) and Smooth Pursuit (SP) eye movements, recorded in the 30min following stimulation. The experiments were carried out in eight healthy volunteers, and eye movements were recorded monocularly with video-oculography. The 40s cTBS significantly increased the amplitude of ipsilateral RS and the acceleration of the ipsilateral SP, and this effect was detectable all over the 30-min recording period; 40s cTBS did not modify the other parameters, namely the peak velocity, the duration and the latency of RS, and the latency and the velocity of SP. The 20s cTBS was ineffective on all RS and SP parameters. Finally, we detected a significant quite-linear reduction of RS peak velocity over time, but this was independent from cTBS and was probably caused by fatigue. The effects of 40 s cTBS in our experiments mimic the disorder of ocular motility in Wallenberg's syndrome and could result from functional impairment of cerebellopontine pathways. This effect lasts 30min at least, and can provide a useful framework for adaptive ocular motor studies.

Interaction between the oculomotor and postural systems during a dual-task: Compensatory reductions in head sway following visually-induced postural perturbations promote the production of accurate double-step saccades in standing human adults.

Humans routinely scan their environment for useful information using saccadic eye movements and/or coordinated movements of the eyes and other body segments such the head and the torso. Most previous eye movement studies were conducted with seated subject and showed that single saccades and sequences of saccades (e.g. double-step saccades) made to briefly flashed stimuli were equally accurate and precise. As one can easily appreciate, most gaze shifts performed daily by a given person are not produced from a seated position, but rather from a standing position either as subjects perform an action from an upright stance or as they walk from one place to another. In the experiments presented here, we developed a new dual-task paradigm in order to study the interaction between the gaze control system and the postural system. Healthy adults (n = 12) were required to both maintain balance and produce accurate single-step and double-step eye saccades from a standing position. Visually-induced changes in head sway were evoked using wide-field background stimuli that either moved in the mediolateral direction or in the anteroposterior direction. We found that, as in the seated condition, single- and double-step saccades were very precise and accurate when made from a standing position, but that a tighter control of head sway was necessary in the more complex double-step saccades condition for equivalent results to be obtained. Our perturbation results support the “common goal” hypothesis that state that if necessary, as was the case during the more complex oculomotor task, context-dependent modulations of the postural system can be triggered to reduced instability and therefore support the accomplishment of a suprapostural goal.

Amplitude and Width Manipulations in Fitts' Paradigm: Comment on Heath et al. (2011) and Heath et al. (2016)

ABSTRACTHeath, Weiler, Marriott, Elliott, and Binstead (2011) and Heath, Samani, Tremblay, and Elliott (2016) have claimed that there are dissociable movement times for amplitude and width manipulations in the Fitts' paradigm. This may to some extent be true, but the Heath et al. (2011) and Heath et al. (2016) data do not support that contention, as shown in this comment. It is shown that data from the research of Heath et al. is not in the range of index of difficulty where ongoing visual control would be used and hence their fits of data to Fitts' law are spurious. The data of Heath et al. (2011) for arm movements and for the primary eye saccade submovements of Heath et al. (2016) are well correlated by the ballistic movement time equation of Hoffmann (1981) and Gan and Hoffmann (1988). When the ballistic equation is used to model data for constant amplitude and constant target width conditions, the effects of the amplitude and width manipulations disappear. Other research indicates that the independent effects of movement amplitude occur due to changes in the time for the distance-covering phase of the movement.

Binocular Fixation Reduces Fixational Eye Movements in the Worst Eye of Patients with Center-Involving Diabetic Macular Edema

Purpose: Treatment of diabetic maculopathy with vascular endothelial growth factor inhibitors is in some patients ineffective, and, therefore, parameters predicting visual outcome after treatment should be identified. It has been shown that fixational saccades are increased in patients with reduced visual acuity secondary to diabetic maculopathy, but it is unknown to what extent these saccades in an eye affected by diabetic maculopathy are influenced by the other eye during binocular fixation. Methods: In 57 eyes from 29 diabetic patients with clinically significant macular edema, fixational eye movements were recorded using the iView X™ video-based eye tracker, and quantitative measures of fixation with the worst eye obtained during monocular and binocular fixation were compared. Results: Fixational saccades during monocular fixation had a significantly higher frequency (p = 0.005), a larger amplitude (p = 0.03), and involved a larger retinal area (p = 0.02) than during binocular fixation. There was a significant negative correlation (r² = 0.18, p = 0.02) between visual acuity and the area of fixation during monocular but not during binocular fixation (r² = 0.007, p = 0.68). Conclusion: Binocular fixation can reduce the area of fixation and the amplitude of fixational saccades in the worst eye of patients with diabetic maculopathy. Fixational saccades in diabetic maculopathy should be studied during monocular fixation.

Rapid and coordinated processing of global motion images by local clusters of retinal ganglion cells.

Even when the body is stationary, the whole retinal image is always in motion by fixational eye movements and saccades that move the eye between fixation points. Accumulating evidence indicates that the brain is equipped with specific mechanisms for compensating for the global motion induced by these eye movements. However, it is not yet fully understood how the retina processes global motion images during eye movements. Here we show that global motion images evoke novel coordinated firing in retinal ganglion cells (GCs). We simultaneously recorded the firing of GCs in the goldfish isolated retina using a multi-electrode array, and classified each GC based on the temporal profile of its receptive field (RF). A moving target that accompanied the global motion (simulating a saccade following a period of fixational eye movements) modulated the RF properties and evoked synchronized and correlated firing among local clusters of the specific GCs. Our findings provide a novel concept for retinal information processing during eye movements.

Vestibular and Oculomotor Assessments May Increase Accuracy of Subacute Concussion Assessment.

In this study, we collected and analyzed preliminary data for the internal consistency of a new condensed model to assess vestibular and oculomotor impairments following a concussion. We also examined this model's ability to discriminate concussed athletes from healthy controls. Each participant was tested in a concussion assessment protocol that consisted of the Neurocom's Sensory Organization Test (SOT), Balance Error Scoring System exam, and a series of 8 vestibular and oculomotor assessments. Of these 10 assessments, only the SOT, near point convergence, and the signs and symptoms (S/S) scores collected following optokinetic stimulation, the horizontal eye saccades test, and the gaze stabilization test were significantly correlated with health status, and were used in further analyses. Multivariate logistic regression for binary outcomes was employed and these beta weights were used to calculate the area under the receiver operating characteristic curve ( area under the curve). The best model supported by our findings suggest that an exam consisting of the 4 SOT sensory ratios, near point convergence, and the optokinetic stimulation signs and symptoms score are sensitive in discriminating concussed athletes from healthy controls (accuracy=98.6%, AUC=0.983). However, an even more parsimonious model consisting of only the optokinetic stimulation and gaze stabilization test S/S scores and near point convergence was found to be a sensitive model for discriminating concussed athletes from healthy controls (accuracy=94.4%, AUC=0.951) without the need for expensive equipment. Although more investigation is needed, these findings will be helpful to health professionals potentially providing them with a sensitive and specific battery of simple vestibular and oculomotor assessments for concussion management.