Video Eye Tracker Research Articles

Covert Tracking to Visual Stimuli in Comatose Patients With Traumatic Brain Injury.

This study investigated video eye tracking (VET) in comatose patients with traumatic brain injury (TBI). We recruited healthy participants and unresponsive patients with TBI. We surveyed the patients' clinicians on whether the patient was tracking and performed the Coma Recovery Scale-Revised (CRS-R). We recorded eye movements in response to motion of a finger, a face, a mirror, and an optokinetic stimulus using VET glasses. Patients were classified as covert tracking (tracking on VET alone) and overt tracking (VET and clinical examination). The ability to obey commands was evaluated at 6-month follow-up. We recruited 20 healthy participants and 10 patients with TBI. The use of VET was feasible in all participants and patients. Two patients demonstrated covert tracking (CRS-R of 6 and 8), 2 demonstrated overt tracking (CRS-R of 22 and 11), and 6 patients had no tracking (CRS-R of 8, 6, 5, 7, 6, and 7). Five of 56 (9%) tracking assessments were missed on clinical examination. All patients with tracking recovered consciousness at follow-up, whereas only 2 of 6 patients without tracking recovered at follow-up. VET is a feasible method to measure covert tracking. Future studies are needed to confirm the prognostic value of covert tracking.

Stratification of Children with Autism Spectrum Disorder Through Fusion of Temporal Information in Eye-gaze Scan-Paths

Background: Looking pattern differences are shown to separate individuals with Autism Spectrum Disorder (ASD) and Typically Developing (TD) controls. Recent studies have shown that, in children with ASD, these patterns change with intellectual and social impairments, suggesting that patterns of social attention provide indices of clinically meaningful variation in ASD. Method: We conducted a naturalistic study of children with ASD (n = 55) and typical development (TD, n = 32). A battery of eye-tracking video stimuli was used in the study, including Activity Monitoring (AM), Social Referencing (SR), Theory of Mind (ToM), and Dyadic Bid (DB) tasks. This work reports on the feasibility of spatial and spatiotemporal scanpaths generated from eye-gaze patterns of these paradigms in stratifying ASD and TD groups. Algorithm: This article presents an approach for automatically identifying clinically meaningful information contained within the raw eye-tracking data of children with ASD and TD. The proposed mechanism utilizes combinations of eye-gaze scan-paths (spatial information), fused with temporal information and pupil velocity data and Convolutional Neural Network (CNN) for stratification of diagnosis (ASD or TD). Results: Spatial eye-gaze representations in the form of scanpaths in stratifying ASD and TD (ASD vs. TD: DNN: 74.4%) are feasible. These spatial eye-gaze features, e.g., scan-paths, are shown to be sensitive to factors mediating heterogeneity in ASD: age (ASD: 2–4 y/old vs. 10–17 y/old CNN: 80.5%), gender (Male vs. Female ASD: DNN: 78.0%) and the mixture of age and gender (5–9 y/old Male vs. 5–9 y/old Female ASD: DNN:98.8%). Limiting scan-path representations temporally increased variance in stratification performance, attesting to the importance of the temporal dimension of eye-gaze data. Spatio-Temporal scan-paths that incorporate velocity of eye movement in their images of eye-gaze are shown to outperform other feature representation methods achieving classification accuracy of 80.25%. Conclusion: The results indicate the feasibility of scan-path images to stratify ASD and TD diagnosis in children of varying ages and gender. Infusion of temporal information and velocity data improves the classification performance of our deep learning models. Such novel velocity fused spatio-temporal scan-path features are shown to be able to capture eye gaze patterns that reflect age, gender, and the mixed effect of age and gender, factors that are associated with heterogeneity in ASD and difficulty in identifying robust biomarkers for ASD.

Using Natural Head Movements to Continually Calibrate EOG Signals.

Electrooculography (EOG) is the measurement of eye movements using surface electrodes adhered around the eye. EOG systems can be designed to have an unobtrusive form-factor that is ideal for eye tracking in free-living over long durations, but the relationship between voltage and gaze direction requires frequent re-calibration as the skin-electrode impedance and retinal adaptation vary over time. Here we propose a method for automatically calibrating the EOG-gaze relationship by fusing EOG signals with gyroscopic measurements of head movement whenever the vestibulo-ocular reflex (VOR) is active. The fusion is executed as recursive inference on a hidden Markov model that accounts for all rotational degrees-of-freedom and uncertainties simultaneously. This enables continual calibration using natural eye and head movements while minimizing the impact of sensor noise. No external devices like monitors or cameras are needed. On average, our method's gaze estimates deviate by 3.54° from those of an industry-standard desktop video-based eye tracker. Such discrepancy is on par with the latest mobile video eye trackers. Future work is focused on automatically detecting moments of VOR in free-living.

Reflexive and volitional saccadic eye movements and their changes in age and progressive supranuclear palsy

Background and objectivesSaccades, rapid movements of the eyes towards a visual or remembered target, are useful in understanding the healthy brain and the pathology of neurological conditions such as progressive supranuclear palsy (PSP). We set out to investigate the parameters of horizontal reflexive and volitional saccades, both visually guided and memory-guided, over a 1 min epoch in healthy individuals and PSP patients. MethodsAn experimental paradigm tested reflexive, volitional visually guided, and volitional memory-guided saccades in young healthy controls (n = 14; 20–31 years), PSP patients (n = 11; 46–75 years) and older age-matched healthy controls (n = 6; 56–71 years). The accuracy and velocity of saccades was recorded using an EyeBrain T2® video eye tracker and analyses performed using the MyEyeAnalysis® software. Two-way analysis of variance (ANOVA) was used to identify significant effects (p < 0.01) between young and older controls to investigate the effects of ageing upon saccades, and between PSP patients and age-matched controls to study the effects of PSP upon saccades. ResultsIn both healthy individuals and PSP patients, volitional saccades are slower and less accurate than reflexive saccades. In PSP patients, accuracy is lower across all saccade types compared to age-matched controls, but velocity is lower only for reflexive saccades. Crucially, there is no change in accuracy or velocity of consecutive saccades over short (one-minute) timescales in controls or PSP patients. ConclusionsVelocity and accuracy of saccades in PSP does not decrease over one-minute timescales, contrary to that previously observed in Parkinson's Disease (PD), suggesting a potential clinical biomarker for the distinction of PSP from PD.

Hierarchical clustering analysis of congenital nystagmus waveforms

Objective: To explore the feasibility of applying machine-learning hierarchical clustering algorithm to waveform-type automatic classification and diagnosis in congenital nystagmus (CN). Methods: A retrospective case series study. A total of 90 patients (90 eyes) diagnosed with CN at Tianjin Eye Hospital from December 2018 to September 2019 were included in the study, including 67 males and 23 females, aged (12±9) years old. Eye movement waveforms were recorded with the video eye tracker in all patients. Analyses with unsupervised machine-learning hierarchical clustering algorithm were performed on the normalized eye movement waveforms. The visualized clustering results were obtained for further waveform naming. The occurrence rate of each waveform type was calculated, and the correlation between the proportion of each waveform type and the visual function of CN patients was analyzed. Independent sample t-test and Pearson correlation analysis were used for statistical analysis. Results: The 46 620 cycles of validated waveforms from the 90 CN patients were categorized into 7 types of waveforms through machine-learning hierarchical clustering algorithm, named type Ⅰ, type Ⅱ, type Ⅲ, and types Ⅳ1-4, respectively. In the 46 620 cycles of eye movement waveforms from the 90 patients with CN, there were 14 259 cycles of type Ⅰ (30.59%), 11 498 cycles of type Ⅱ (24.66%), 4 083 cycles of type Ⅲ (8.76%), 5 430 cycles of type Ⅳ1 (11.65%), 3 451 cycles of type Ⅳ2 (7.40%), 3 015 cycles of type Ⅳ3 (6.47%), 2 663 cycles of type Ⅳ4 (5.71%) and 2 221 cycles of unclassified waveforms (4.76%). The waveforms of types Ⅰ, Ⅱ and Ⅲ corresponded to the 3 basic CN eye movement waveforms (velocity-increasing jerk waveform, velocity-decreasing jerk waveform and pendular waveform) described in the textbooks, and the waveforms of types Ⅳ1-4 were complex waveforms. The proportions of patients with the 7 types of waveforms were 78.89% (71 cases), 41.11% (37 cases), 17.78% (16 cases), 20.00% (18 cases), 7.78% (7 cases), 15.56% (14 cases) and 11.11% (10 cases), respectively. According to the results of automatic classification, 38 (42.22%) CN patients presented with only one type of waveforms, and the remaining 52 (57.78%) CN patients presented with two or more types of waveforms, including 23 (25.56%) patients with 3 or more types of waveforms and 5 (5.56%) patients with 4 types of waveforms. The proportions of type Ⅰ component were significantly correlated with the patients' best corrected visual acuities (BCVAs;logarithm of the minimum angle of resolution) (r=-0.39; P<0.01), and there was no relationship between the proportions of type Ⅱ component and the patients' BCVAs (P>0.05). The BCVAs of the patients with type Ⅰ as the dominant component were better than those of the patients with type Ⅱ as the dominant component, with statistically significant difference (0.19±0.14 vs. 0.45±0.37;t=2.77; P<0.05). Conclusion: Machine-learning hierarchical clustering algorithm can be used for waveform-type automatic classification and discrimination in CN and provide an auxiliary method for the precise diagnosis and evaluation of the disease.

An Eye-Tracking Study on the Effect of Different Signalized Intersection Typologies on Pedestrian Performance

Pedestrian safety is a well-known issue, such that many road safety associations emphasize measures to improve this aspect. One of the main conflict points is pedestrian crossings, where motorized and non-motorized traffic flows directly interact and where pedestrian attention and reaction are two elements that can strongly influence their safety. Nowadays, these aspects are often deviated by the use of smartphones to surf the Internet or social media. The aim of the present study is to find out (1) whether and how intersection typology affects pedestrian behavior, both in terms of attention and crossing performance, and (2) whether and how gaze and behavioral characteristics are affected by smartphone use and social media browsing. To achieve this goal, eye-tracking technology was used to obtain qualitative and quantitative information on the number of fixations, their duration, and reaction times of pedestrians. Additionally, from the eye-tracking videos, it was possible to derive pedestrian waiting times, crossing times, and speeds. Statistical tests were conducted to determine if there is a significant difference in pedestrian behavior at the three different types of intersections and in their behavior when using or not using their device. Results confirm the initial hypotheses and quantify the difference in pedestrian gaze behavior and crossing performance when walking across three different types of signalized crosswalks.

Students\u2019 collaborative creative process and its phases in mathematics: an explorative study using dual eye tracking and stimulated recall interviews

In the age of artificial intelligence where standard problems are increasingly processed by computers, creative problem solving, the ability to think outside the box is in high demand. Collaboration is also increasingly significant, which makes creative collaboration an important twenty-first-century skill. In the research described in this paper, we investigated students’ collaborative creative process in mathematics and explored the collaborative creative process in its phases. Since little is known about the collaborative creative process, we conducted an explorative case study, where two students jointly worked on a multiple solution task. For in-depth insight into the dyad’s collaborative creative process, we used a novel research design in mathematics education, DUET SRI: both students wore eye-tracking glasses during their collaborative work for dual eye-tracking (DUET) and they each participated in a subsequent stimulated recall interview (SRI) where eye-tracking videos from their joint work served as stimulus. Using an inductive data analysis method, we then identified the phases of the students’ collaborative creative process. We found that the collaborative creative process and its phases had similarities to those previously found for solo creative work, yet the process was more complex and volatile and involved different branches. Based on our findings, we present a tentative model of the dyad’s collaborative process in its phases, which can help researchers and educators trace and foster the collaborative creative process more effectively.

Microsaccadic Fixational Eye Movements as an Oculomotor Marker for Concussion

To identify whether concussion causes abnormalities in fixational eye movements, specifically the generation of microsaccades. Microsaccades are microscopic rapid eye movements that occur normally with attempted fixation. However, changes in microsaccade rate, magnitude, etc have been linked with neurologic and ophthalmic pathologies. We collected baseline data for college athletes (n = 116) at Sterling College (Sterling, KS) as they reported for the physical examination before the beginning of the athletic season. None of the athletes had a prior history of concussion. Concussion patients (n = 86) were selected from patients who had an initial visit for concussion at a private concussion clinic. Patients were included if they presented within 50 days of injury. All participants were between 18 and 23 years of age. For each participant we measured the number of saccades generated, the size and speed of the micro saccades, the area covered and the ratio of vertical-to-horizontal direction component of the fixational eye movements, using a 250 Hz video-eye tracker mounted inside a HTC Vive VR headset. Participants were instructed to fixate on a central dot for 140 seconds, in 20-second intervals. We performed a logistic regression with the log-transformed oculomotor characteristics as independent variables and concussion yes/no as dependent variables. Errors are presented as standard error from the mean. The average microsaccade magnitude was higher in concussed than in non-concussed participants (1.85 ± 0.12° vs 1.32 ± 0.06°, p < 0.001). Similarly, the fixational eye movements (microsaccades + drifts) of concussed patients tended to cover a more vertical area during fixation periods (vertical-to-horizontal ratio of 3.49 ± 0.94 vs 1.12 ± 0.04, p < 0.005). Oculomotor testing, specifically microsaccades is a potential marker for concussion. Concussion patients present larger and more vertical eye movements during fixation.

Video Compression for Screen Recorded Sequences Following Eye Movements

With the advent of smartphones and tablets, video traffic on the Internet has increased enormously. With this in mind, in 2013 the High Efficiency Video Coding (HEVC) standard was released with the aim of reducing the bit rate (at the same quality) by 50% with respect to its predecessor. However, new contents with greater resolutions and requirements appear every day, making it necessary to further reduce the bit rate. Perceptual video coding has recently been recognized as a promising approach to achieving high-performance video compression and eye tracking data can be used to create and verify these models. In this paper, we present a new algorithm for the bit rate reduction of screen recorded sequences based on the visual perception of videos. An eye tracking system is used during the recording to locate the fixation point of the viewer. Then, the area around that point is encoded with the base quantization parameter (QP) value, which increases when moving away from it. The results show that up to 31.3% of the bit rate may be saved when compared with the original HEVC-encoded sequence, without a significant impact on the perceived quality.

A CNN and LSTM Network for Eye-Blink Classification from MRI Scanner Monitoring Videos.

Eye closure changes brain activity, so eye-blink tracking of subjects undergoing resting-state functional magnetic resonance imaging (fMRI) is relevant for identifying when a subject blinks, falls asleep, or keeps their eyes closed. Existing MRI eye-tracking solutions use commercially available MR-compatible video cameras with tracking software that can fail on low-quality videos. In this paper, we propose a two-stage convolutional recurrent neural network to classify open and closed eyes from frames of MRI eye-tracking videos under variable camera conditions. The model extracts visual features from each video frame using a convolutional neural network based on the Inception-v3 model, then uses a long short-term memory network to incorporate temporal information encoded in the sequence of visual features over time. Our model is implemented in Keras and demonstrated on a dataset of MRI eye-tracking videos from the Human Connectome Project. We manually labelled frames from the dataset for training and evaluation. The network was able to classify eye-blink states with a precision of 0.739 and recall of 0.835 on a previously unseen holdout dataset under varying camera conditions, eye position, and video quality.Clinical relevance- Functional mapping studies in psychiatry and neuro-development which rely on a resting state fMRI protocol may yield divergent results depending on whether the subject keeps their eyes closed or open or whether the subject falls asleep. The clinical relevance of this work is to introduce the eye state (closed or open) in brain imaging studies as a prospective covariate, and as a feature that can potentially control for sleep state as a confounding factor.

Alertness and Visual Attention Impact Different Aspects of the Optokinetic Reflex.

PurposeAssessing visual attention and alertness is of great importance in visual and cognitive neuroscience, providing objective measures valuable for both researchers and clinicians. This study investigates how the optokinetic response differs between levels of visual attention in healthy adults while controlling for alertness.MethodsTwelve healthy subjects (8 men and 4 women; mean age = 33 ± 9.36) with intact gaze-stability, visual acuity, and binocularity were recruited. Subjects viewed a rotating visual scene provoking torsional optokinetic nystagmus (OKN) while wearing a video eye tracker in a seated head-fixed position. Tasks requiring focused, neutral, and divided visual attention were issued to each subject and the OKN was recorded. Pupil sizes were monitored as a proxy for alertness.ResultsPupil dilation was increased for both focused and divided visual attention. The number of nystagmus beats was highest for the focused condition and lowest for the divided attentional task. OKN gain was increased during both focused and divided attention. The distribution of nystagmus beats over time showed that only focused attention produced a reliable adaptation of the OKN.ConclusionsResults consequently indicate that OKN frequency is adaptive to a viewer's level of visual attention, whereas OKN gain is influenced by alertness levels. This pattern offers insight into the neural processes integrating visual input with reflexive motor responses. For example, it contextualizes why attention to visual stimuli can cause dizziness, as the OKN frequency reflects activity of the velocity storage mechanism. Additionally, the OKN could offer a possible venue for differentiating between visual attention and alertness during psychometric testing.

Improving Airline Pilots’ Visual Scanning and Manual Flight Performance through Training on Skilled Eye Gaze Strategies

Poor cockpit monitoring has been identified as an important contributor to aviation accidents. Improving pilots’ monitoring strategies could therefore help to enhance flight safety. During two different sessions, we analyzed the flight performance and eye movements of professional airline pilots in a full-flight simulator. In a pre-training session, 20 pilots performed a manual approach scenario as pilot flying (PFs) and were classified into three groups according to their flight performance: unstabilized, standard, and most accurate. The unstabilized pilots either under- or over-focused various instruments. Their number of visual scanning patterns was lower than those of pilots who managed to stabilize their approach. The most accurate pilots showed a higher perceptual efficiency with shorter fixation times and more fixations on important primary flight instruments. Approximately 10 months later, fourteen pilots returned for a post-training session. They received a short training program and performed a similar manual approach as during the pre-training session. Seven of them, the experimental group, received individual feedback on their own performance and visual behavior (i.e., during the pre-training session) and a variety of data obtained from the most accurate pilots, including an eye-tracking video showing efficient visual scanning strategies from one of the most accurate pilots. The other seven, the control group, received general guidelines on cockpit monitoring. During the post-training session, the experimental group had better flight performance (compared to the control group), and its visual scanning strategies became more similar to those of the most accurate pilots. In summary, our results suggest that cockpit monitoring underlies manual flight performance and that it can be improved using a training program based mainly on exposure to eye movement examples from highly accurate pilots.

Student's Perspective and Teachers' Metacognition: Applications of Eye-Tracking in Education and Scientific Research in Schools.

This Perspective article discusses the possible contributions of eye-tracking (ET) to the field of Educational Neuroscience based on an application of this tool at schools. We sought to explore the teachers’ view of ET videos recorded while students solved mathematical problems. More than 90% of the teachers could predict with great accuracy whether the students had answered the questions correctly or not based solely on the information provided by the ET videos. Almost all participants tried to translate the students’ thoughts to understand the strategy used by the children. Our results highlight the relevance of qualitative analysis to identify the gaze strategies used by students. We propose that ET allows teachers to gain critical feedback about students’ behavior during problem-solving. Most previous studies tend to emphasize the benefits of ET applications to explore learners’ cognition. Our findings point that this system can also be useful to investigate teachers’ cognition by providing metacognitive experiences.

The Feasibility of Using Virtual Reality and Eye Tracking in Research With Older Adults With and Without Alzheimer's Disease.

Aim: To examine the feasibility of using large scale spatial, self-mobile, virtual reality, and eye tracking in older adults with and without Alzheimer's disease (AD).Methods: Older adults with early stage AD (n = 38) and a control group without AD (n = 50) were asked to find their way in a large, projected VR simulation of a retirement community repeatedly over 10 trials for each of 2 days, while wearing eye tracking glasses. Feasibility measures, including tolerance, side effects, and ability to complete the VR and eye tracking were collected. This study reports the analysis of the feasibility data for the VR and eye tracking and comparison of findings between the groups.Results: Over 80% of the subjects were able to complete the VR portion of the study. Only four subjects, all in the AD group, could not use the joystick and were excluded. Withdrawal rate (18%) was similar between the groups [X2(2) = 2.82, N = 88, p = 0.245] with most withdrawals occurring after the fourth trial. Simulation sickness was not significantly different between the groups. Only 60% of the subjects had completed eye tracking videos; more subjects in the AD group had complete eye tracking videos than the control group; X2(1) = 7.411, N = 88, p = 0.006. Eye tracking incompletion was primarily due to inability to calibration issues.Conclusion: Virtual reality testing and eye tracking can be used in older adults with and without AD in a large-scale way-finding task, but that there are some limitations.

Evaluation of the Hazard Perception Skills of Young Drivers

Abstract The aim of this study is to collate valuable information about the hazard perception process of (young) drivers and to evaluate their hazard perception skills. For this, an eye-tracking system was used to record the visual behaviour of drivers. In addition, a system based on a data logger and sensors was developed to capture and log the relevant data from the vehicle. By tapping into the vehiclés CAN bus (Controller Area Network), the needed parameters (e.g. position of accelerator, brake, and clutch pedal, as well as the steering wheel angle) were acquired through the reverse engineering of the vehicle′s CAN stream. All the captured data was subsequently synchronized and overlaid in the eye-tracking video. The complete system, i.e. data-logger and sensors, was consistently integrated into a driving school car. Due to the fact that all the data was captured in real-time whilst driving in traffic, every analysed situation can be considered unique and therefore cannot be compared to other situations. The results of the study revealed that only in 18% of the analysed situations, the hazard-perception skills were adequate or the same as they were taught at the driving school just a few months previous. Confronted by the videos of their lessons, the participating drivers adjusted their self-assessment scores for their driving skills downwards by around 25% on average.

Eye-tracking glasses in face-to-face interactions: Manual versus automated assessment of areas-of-interest

The assessment of gaze behaviour is essential for understanding the psychology of communication. Mobile eye-tracking glasses are useful to measure gaze behaviour during dynamic interactions. Eye-tracking data can be analysed by using manually annotated areas-of-interest. Computer vision algorithms may alternatively be used to reduce the amount of manual effort, but also the subjectivity and complexity of these analyses. Using additional re-identification (Re-ID) algorithms, different participants in the interaction can be distinguished. The aim of this study was to compare the results of manual annotation of mobile eye-tracking data with the results of a computer vision algorithm. We selected the first minute of seven randomly selected eye-tracking videos of consultations between physicians and patients in a Dutch Internal Medicine out-patient clinic. Three human annotators and a computer vision algorithm annotated mobile eye-tracking data, after which interrater reliability was assessed between the areas-of-interest annotated by the annotators and the computer vision algorithm. Additionally, we explored interrater reliability when using lengthy videos and different area-of-interest shapes. In total, we analysed more than 65 min of eye-tracking videos manually and with the algorithm. Overall, the absolute normalized difference between the manual and the algorithm annotations of face-gaze was less than 2%. Our results show high interrater agreements between human annotators and the algorithm with Cohen’s kappa ranging from 0.85 to 0.98. We conclude that computer vision algorithms produce comparable results to those of human annotators. Analyses by the algorithm are not subject to annotator fatigue or subjectivity and can therefore advance eye-tracking analyses.

Shared Gaze Visualizations in Collaborative Interactions: Past, Present and Future

AbstractThe past decade has witnessed a growing interest for using dual eye tracking to understand and support remote collaboration, especially with studies that have established the benefits of displaying gaze information for small groups. While this line of work is promising, we lack a consistent framework that researchers can use to organize and categorize studies on the effect of shared gaze on social interactions. There exists a wide variety of terminology and methods for describing attentional alignment; researchers have used diverse techniques for designing gaze visualizations. The settings studied range from real-time peer collaboration to asynchronous viewing of eye-tracking video of an expert providing explanations. There has not been a conscious effort to synthesize and understand how these different approaches, techniques and applications impact the effectiveness of shared gaze visualizations (SGVs). In this paper, we summarize the related literature and the benefits of SGVs for collaboration, describe important terminology as well as appropriate measures for the dual eye-tracking space and discuss promising directions for future research. As eye-tracking technology becomes more ubiquitous, there is pressing need to develop a consistent approach to evaluation and design of SGVs. The present paper makes a first and significant step in this direction.

Torsional component of microsaccades during fixation and quick phases during optokinetic stimulation.

While many studies have characterized the eye movements during visual fixation, includ-ing microsaccades, in most cases only horizontal and vertical components have been rec-orded and analyzed. Thus, little is known about the torsional component of microsaccades. We took advantage of a newly developed software and hardware to record eye movements around the three axes of rotation during fixation and torsional optokinetic stimulus. We found that the average amplitude of the torsional component of microsaccades during fixation was 0.34 ± 0.07 degrees with velocities following a main sequence with a slope comparable to the horizontal and vertical components. We also found the size of the tor-sional displacement during microsaccades was correlated with the horizontal but not the vertical component. In the presence of an optokinetic stimulus a nystagmus was induced producing a more frequent and larger torsional quick phases compared to microsaccades produced during fixation with a stationary stimulus. The torsional component and the vertical vergence component of quick phases grew larger with higher velocities. Addition-ally, our results validate and show the feasibility of recording torsional eye movements using video eye tracking in a desktop mounted setup.

Spontaneous visual exploration during locomotion in patients with phobic postural vertigo

BackgroundEarlier studies on stance and gait with posturographic and EMG-recordings and automatic gait analysis in patients with phobic postural vertigo (PPV) or visual height intolerance (vHI) revealed similar patterns of body stiffening with muscle co-contraction and a slow, cautious gait. Visual exploration in vHI patients was characterized by a freezing of gaze-in-space when standing and reduced horizontal eye and head movements during locomotion.ObjectiveBased on the findings in vHI patients, the current study was performed with a focus on visual control of locomotion in patients with PPV while walking along a crowded hospital hallway.MethodsTwelve patients with PPV and eleven controls were recruited. Participants wore a mobile infrared video eye-tracking system that continuously measured eye-in-head movements in the horizontal and vertical planes and head orientation and motion in the yaw, pitch, and roll planes. Visual exploration behavior of participants was recorded at the individually preferred speed for a total walking distance of 200 m. Gaze-in-space directions were determined by combining eye-in-head and head-in-space orientation. Walking speeds were calculated based on the trial duration and the total distance traversed. Participants were asked to rate their feelings of discomfort during the walk on a 4-point numeric rating scale. The examiners rated the crowdedness of the hospital hallway on a 4-point numeric rating scale.ResultsThe major results of visual exploration behavior in patients with PPV in comparison to healthy controls were: eye and head positions were directed more downward in the vertical plane towards the ground ahead with increased frequency of large amplitude vertical orientation movements towards the destination, the end of the ground straight ahead. The self-adjusted speed of locomotion was significantly lower in PPV. Particularly those patients that reported high levels of discomfort exhibited a specific visual exploration of their horizontal surroundings. The durations of fixating targets in the visual surroundings were significantly shorter as compared to controls.ConclusionGaze control of locomotion in patients with PPV is characterized by a preferred deviation of gaze more downward and by horizontal explorations for suitable auxiliary means for potential postural support in order to prevent impending falls. These eye movements have shorter durations of fixation as compared to healthy controls and patients with vHI. Finally, the pathological alterations in eye–head coordination during locomotion correlate with a higher level of discomfort and anxiety about falling.

Longitudinal changes in binocular coordination of smooth pursuit in patients with intermittent exotropia after strabismus surgery

To observe the change in horizontal smooth pursuit in patients with intermittent exotropia before and after strabismus surgery. The smooth pursuit of patients with intermittent exotropia was recorded using a video eye-tracker before and 1week, and 1, 3, and 6months after strabismus surgery. Subjects were asked to track a step-ramp target moving at ±6.1°/sec horizontally as accurately as possible under binocular viewing. The differences in gain (eye velocity divided by target velocity) and amplitude of smooth pursuit between right and left eyes before and after surgery were compared. A total of 9 patients (mean age, 22.2±13.9years) were included. Mean preoperative ocular alignment at near was 59.1Δ ± 34.7Δ. The difference in gain between the left and right eyes before surgery was 0.23±0.1; in amplitude, 3.0° ± 3.7°. These values were improved at 1week after surgery (gain, 0.08±0.06; amplitude, 0.9°±0.65°) and continued to improve for 6months after surgery; however, ocular alignment at near reverted from 5.9Δ±10.5Δ to 18.9Δ±17.5Δ by 6months after surgery. In this small patient cohort, surgical correction of ocular alignment improved binocular coordination of smooth pursuit in intermittent exotropia. In the long term, the improvement of the binocular coordination of smooth pursuit tended to remain, although the eye position partially reverted to the presurgical state.