Eye Movements In Order Research Articles

Influence of Task-evoked Mental Workloads on Oculo-motor indices and their connections

The frequency of microsaccades is often used as a measurement of eye movement in order to estimate the level of effort required, because some indices of oculo-motors suggest the level of mental activity. In an experiment involving several task-manipulation levels, ocular information including micros

Biomimetic eye modeling & deep neuromuscular oculomotor control

We present a novel, biomimetic model of the eye for realistic virtual human animation. We also introduce a deep learning approach to oculomotor control that is compatible with our biomechanical eye model. Our eye model consists of the following functional components: (i) submodels of the 6 extraocular muscles that actuate realistic eye movements, (ii) an iris submodel, actuated by pupillary muscles, that accommodates to incoming light intensity, (iii) a corneal submodel and a deformable, ciliary-muscle-actuated lens submodel, which refract incoming light rays for focal accommodation, and (iv) a retina with a multitude of photoreceptors arranged in a biomimetic, foveated distribution. The light intensity captured by the photoreceptors is computed using ray tracing from the photoreceptor positions through the finite aperture pupil into the 3D virtual environment, and the visual information from the retina is output via an optic nerve vector. Our oculomotor control system includes a foveation controller implemented as a locally-connected, irregular Deep Neural Network (DNN), or "LiNet", that conforms to the nonuniform retinal photoreceptor distribution, and a neuromuscular motor controller implemented as a fully-connected DNN, plus auxiliary Shallow Neural Networks (SNNs) that control the accommodation of the pupil and lens. The DNNs are trained offline through deep learning from data synthesized by the eye model itself. Once trained, the oculomotor control system operates robustly and efficiently online. It innervates the intraocular muscles to perform illumination and focal accommodation and the extraocular muscles to produce natural eye movements in order to foveate and pursue moving visual targets. We additionally demonstrate the operation of our eye model (binocularly) within our recently introduced sensorimotor control framework involving an anatomically-accurate biomechanical human musculoskeletal model.

Salience drives overt selection of two equally relevant visual targets.

In the present study, we investigated whether salience determines the sequence of selection when participants search for two equally relevant visual targets. To do this, attentional selection was tracked overtly as observers inspected two items of differing physical salience: one a highly salient color singleton, and the other a less salient shape singleton. Participants were instructed to make natural eye movements in order to determine whether two line segments contained within the two singletons were oriented in the same or in different directions. Because both singleton items were task-relevant, participants had no reason to inspect one item before the other. As expected, observers fixated both targets on the majority of trials. Critically, saccades to the color singleton preceded saccades to the less salient shape singleton on the majority of trials. This demonstrates that the order of attentional object selection is largely determined by stimulus salience when task relevance is equated.

Decoding Target Distance and Saccade Amplitude from Population Activity in the Macaque Lateral Intraparietal Area (LIP).

Primates perform saccadic eye movements in order to bring the image of an interesting target onto the fovea. Compared to stationary targets, saccades toward moving targets are computationally more demanding since the oculomotor system must use speed and direction information about the target as well as knowledge about its own processing latency to program an adequate, predictive saccade vector. In monkeys, different brain regions have been implicated in the control of voluntary saccades, among them the lateral intraparietal area (LIP). Here we asked, if activity in area LIP reflects the distance between fovea and saccade target, or the amplitude of an upcoming saccade, or both. We recorded single unit activity in area LIP of two macaque monkeys. First, we determined for each neuron its preferred saccade direction. Then, monkeys performed visually guided saccades along the preferred direction toward either stationary or moving targets in pseudo-randomized order. LIP population activity allowed to decode both, the distance between fovea and saccade target as well as the size of an upcoming saccade. Previous work has shown comparable results for saccade direction (Graf and Andersen, 2014a,b). Hence, LIP population activity allows to predict any two-dimensional saccade vector. Functional equivalents of macaque area LIP have been identified in humans. Accordingly, our results provide further support for the concept of activity from area LIP as neural basis for the control of an oculomotor brain-machine interface.

Gaze direction when driving after dark on main and residential roads: Where is the dominant location?

CIE Joint Technical Committee JTC-1 has requested data regarding the size and shape of the distribution of drivers’ eye movement in order to characterize visual adaptation. This paper reports the eye movement of drivers along two routes in Berlin after dark, a main road and a residential street, captured using eye tracking. It was found that viewing behaviour differed between the two types of road. On the main road eye movement was clustered within a circle of approximately 10° diameter, centred at the horizon of the lane. On the residential street eye movement is clustered slightly (3.8°) towards the near side, eye movements were best captured with either an ellipse of approximate axes 10° vertical and 20° horizontal, centred on the lane ahead, or a 10° circle centred 3.8° towards the near side. These distributions reflect a driver’s tendency to look towards locations of anticipated hazards.

The impact of red light running camera flashes on younger and older drivers' attention and oculomotor control.

Recent empirical evidence has suggested that the flashes associated with red light running cameras (RLRCs) distract younger drivers, pulling attention away from the roadway and delaying processing of safety-relevant events. Considering the perceptual and attentional declines that occur with age, older drivers may be especially susceptible to the distracting effects of RLRC flashes, particularly in situations in which the flash is more salient (a bright flash at night compared with the day). The current study examined how age and situational factors potentially influence attention capture by RLRC flashes using covert (cuing effects) and overt (eye movement) indices of capture. We manipulated the salience of the flash by varying its luminance and contrast with respect to the background of the driving scene (either day or night scenes). Results of 2 experiments suggest that simulated RLRC flashes capture observers' attention, but, surprisingly, no age differences in capture were observed. However, an analysis examining early and late eye movements revealed that older adults may have been strategically delaying their eye movements in order to avoid capture. Additionally, older adults took longer to disengage attention following capture, suggesting at least 1 age-related disadvantage in capture situations. Findings have theoretical implications for understanding age differences in attention capture, especially with respect to capture in real-world scenes, and inform future work that should examine how the distracting effects of RLRC flashes influence driver behavior.

The human balance system and gender.

The human body balance system is a complex system of organs and mechanisms, which generate postural reactions to counter the displacement from the equilibrium position of the body centre of gravity, and which control eye movement in order to maintain a stable image of the environment. Computerised Dynamic Posturography (CDP) allows for a quantitative and objective assessment of the sen- sory and motor components of the body balance control system as well as of the integration and adaptive mechanisms in the central nervous system. The aim of this study was to determine the differences, when maintaining body balance, based on the gender of young, healthy people using CDP. The study was carried out on a group of 43 healthy subjects by comparing the effectiveness of the balance system in 22 women and 21 men aged between 20 and 26 years, between 171 and 177 cm in height, and without any clinical symptoms of balance disorders. The men and women were selected such that they did not differ significantly in height and BMI. Using the Equitest posturograph manufactured by NeuroCom International Inc. the following tests were performed: Sensory Organisation Test (SOT), Motor Control Test (MCT) and the Adaptation Test (ADT). The gender of young healthy individuals without any clinical symptoms of balance disorders also does not affect the effectiveness of the sensory system and the use of this signal in maintaining body balance.

Face Recognition Increases during Saccade Preparation

Face perception is integral to human perception system as it underlies social interactions. Saccadic eye movements are frequently made to bring interesting visual information, such as faces, onto the fovea for detailed processing. Just before eye movement onset, the processing of some basic features, such as the orientation, of an object improves at the saccade landing point. Interestingly, there is also evidence that indicates faces are processed in early visual processing stages similar to basic features. However, it is not known whether this early enhancement of processing includes face recognition. In this study, three experiments were performed to map the timing of face presentation to the beginning of the eye movement in order to evaluate pre-saccadic face recognition. Faces were found to be similarly processed as simple objects immediately prior to saccadic movements. Starting ∼ 120 ms before a saccade to a target face, independent of whether or not the face was surrounded by other faces, the face recognition gradually improved and the critical spacing of the crowding decreased as saccade onset was approaching. These results suggest that an upcoming saccade prepares the visual system for new information about faces at the saccade landing site and may reduce the background in a crowd to target the intended face. This indicates an important role of pre-saccadic eye movement signals in human face recognition.

Functional role and implications of population heterogeneity on vestibular ocular reflex response fidelity

Evidence for a functional role of population variance and heterogeneity in sensori-motor systems is currently emerging [1]. The vestibular-ocular reflex (VOR) is a sensori-motor reflex characterised by high fidelity, low latency compensatory eye movements in response to head movements. A major component of the VOR is the linear, rotational reflex, which produces eye movements in order to compensate for angular head rotations [2]. This linear, rotational component of the VOR is produced through an elementary 3 neuron arc. However, single cell responses of the vestibular nucleus neurons involved show non-linearity and distortion for high frequency inputs [3] suggesting, instead, that the required signal transmission is achieved by response of a population of neurons [4]. Using biophysically complete, compartmental models of medial vestibular nucleus (MVN) neurons, utilising the Hodgkin-Huxley formulation applied to a range of ionic currents, we investigate the effects of variance and heterogeneity of ion channel density in producing and maintaining asynchronicity of the population, and the effect of this on the response fidelity of the population to a broad range of input frequencies. Inputs used take the form of both sinusoidal current injection, as well as driving of the cell model through synaptic input. It will be shown that heterogeneous populations, where each member shows a different rate of spontaneous activity, produces a response with greater fidelity than homogeneous populations, in which firing regularity is the same across the population. This heterogeneity in the populations is produced through the variance of calcium activated potassium channels, present in both the somatic and dendritic compartments of the model, involved in the second phase of a biphasic action potential. The ranges and distributions of variance across populations will be discussed in terms of optimisation and tuning of the circuits involved in the response. In addition, various commonly used methods for the analysis and estimation of the population response are discussed in regards to their suitability, accuracy and inherent limitations. Finally, techniques for the analysis involving the use of optimal digital filters will be discussed.

Influence of postural constraints on eye and head latency during voluntary rotations

Redirecting gaze towards new targets often requires not only eye movements, but also synergistic rotations of the head, trunk and feet. This study investigates the influence of postural constraints on eye and head latency during voluntary refixations in the horizontal plane in 14 normal subjects. Three postural conditions were presented, (1) sitting in a chair using only eye and head movements, (2) standing without feet movements and (3) standing with feet movement. Head–eye reorientations towards eccentric un-predictable locations were performed towards ±45° and ±90° targets and back towards a central, spatially predictable target. Results showed that postural constraints affected eye latency but only when subjects knew the future location of the target (recentering “return” trials). Specifically, relatively longer eye latencies were observed when subjects had to turn their feet back towards the predictable central target. These findings suggest that the additional CNS processing required to reduce degrees of freedom during predictive motion introduces delays to the eye movement in order to efficiently assemble the components of a new motor synergy.

Predictability of visual perturbation during locomotion: implications for corrective efference copy signaling

In guiding adaptive behavior, efference copy signals or corollary discharge are traditionally considered to serve as predictors of self-generated sensory inputs and by interfering with their central processing are able to counter unwanted consequences of an animal's own actions. Here, in a speculative reflection on this issue, we consider a different functional role for such intrinsic predictive signaling, namely in stabilizing gaze during locomotion where resultant changes in head orientation in space require online compensatory eye movements in order to prevent retinal image slip. The direct activation of extraocular motoneurons by locomotor-related efference copies offers a prospective substrate for assisting self-motion derived sensory feedback, rather than being subtracted from the sensory signal to eliminate unwanted reafferent information. However, implementing such a feed-forward mechanism would be critically dependent on an appropriate phase coupling between rhythmic propulsive movement and resultant head/visual image displacement. We used video analyzes of actual locomotor behavior and basic theoretical modeling to evaluate head motion during stable locomotion in animals as diverse as Xenopus laevis tadpoles, teleost fish and horses in order to assess the potential suitability of spinal efference copies to the stabilization of gaze during locomotion. In all three species, and therefore regardless of aquatic or terrestrial environment, the head displacements that accompanied locomotor action displayed a strong correlative spatio-temporal relationship in correspondence with a potential predictive value for compensatory eye adjustments. Although spinal central pattern generator-derived efference copies offer appropriately timed commands for extraocular motor control during self-generated motion, it is likely that precise image stabilization requires the additional contributions of sensory feedback signals. Nonetheless, the predictability of the visual consequences of stereotyped locomotion renders intrinsic efference copy signaling an appealing mechanism for offsetting these disturbances, thus questioning the exclusive role traditionally ascribed to sensory-motor transformations in stabilizing gaze during vertebrate locomotion.

Predictive saccade in the absence of smooth pursuit: interception of moving targets in the archer fish

Interception of fast-moving targets is a demanding task many animals solve. To handle it successfully, mammals employ both saccadic and smooth pursuit eye movements in order to confine the target to their area centralis. But how can non-mammalian vertebrates, which lack smooth pursuit, intercept moving targets? We studied this question by exploring eye movement strategies employed by archer fish, an animal that possesses an area centralis, lacks smooth pursuit eye movements, but can intercept moving targets by shooting jets of water at them. We tracked the gaze direction of fish during interception of moving targets and found that they employ saccadic eye movements based on prediction of target position when it is hit. The fish fixates on the target's initial position for ∼0.2 s from the onset of its motion, a time period used to predict whether a shot can be made before the projection of the target exits the area centralis. If the prediction indicates otherwise, the fish performs a saccade that overshoots the center of gaze beyond the present target projection on the retina, such that after the saccade the moving target remains inside the area centralis long enough to prepare and perform a shot. These results add to the growing body of knowledge on biological target tracking and may shed light on the mechanism underlying this behavior in other animals with no neural system for the generation of smooth pursuit eye movements.

Handmade Infrared Rays Complementary Metal Oxide Semiconductor (IR-CMOS) Camera for Recording Eye Movements

Objective: It is important to observe eye movements in order to evaluate peripheral or central vestibular disorders in dizzy patients. An infrared rays charge coupling device (IR-CCD) camera is now widely used in daily practice. The technical advantage of a complementary metal oxide semiconductor (CMOS) now allows us to develop an inexpensive handmade camera for carrying out nystagmus recordings. Methods: We developed a handmade IR-CMOS camera at a reasonable cost of less than $150. The costs of a small IR- CMOS camera, scuba diving goggles, an AC adapter, an audiovisual (AV) cord, and a plastic board with a thickness of 0.5 mm were $60, $60, $10, $10, and $10, respectively. It takes almost an hour to assemble the camera. We recorded eye movements using this camera. Results: The image obtained using this inexpensive handmade camera was clear and highly comparable to that obtained using a conventional IR-CCD camera. Conclusion: The handmade IR-CMOS camera is inexpensive, easy to develop, and can be effectively used in daily practice. In future, with technical developments in electronics, we intend to develop a more compact and high-quality camera for recording eye movements.

The contribution of the fixational eye movements to the variability of the measured ocular aberration

The purpose of this work is to analyze the contribution of eye movements to the variability of the Zernike coefficients as determined with a Hartmann-Shack aberrometer. In order to isolate this effect we considered static aberrations tied to the eye pupil. We used several eye movements of different magnitude, both synthetic and corresponding to actual series recorded in our laboratory with different subjects. Our results show the relevance of the modal coupling induced by the estimation process and the benefit of correcting eye movements in order to get a better estimate of the ocular aberrations. They also show that eye movements during aberrometric measurements are an important source of apparent wavefront variability.

Saccadic and smooth pursuit eye movements: Computational modeling of a common inhibitory mechanism in brainstem

The oculomotor system coordinates different types of eye movements in order to orient the visual axis, including saccade and smooth pursuit,. It was traditionally thought that the premotor pathways for these different eye movements are largely separate. In particular, a group of midline cells in the pons called omnipause neurons were considered to be part of only the saccadic system. Recent experimental findings have shown activity modulation of these brainstem premotor neurons during both kinds of eye movements. In this study, we propose a new computational model of the brainstem circuitry underlying the generation of saccades and smooth pursuit eye movements. Similar models have been developed earlier, but mainly looking at pure saccades. Here, we integrated recent neurophysiological findings on omnipause neuron activity during smooth pursuit. Our computational model can mimic some new experimental findings as the similarity of “eye velocity profile” with “omnipause neuron pattern of activity” in pursuit movement. We showed that pursuit neuron activity is augmented during catch-up saccades; this increment depends on the initial pursuit velocity in catch-up saccade onset. We conclude that saccadic and pursuit components of catch-up saccades are added to each other nonlinearly.

The use of infrared oculography to study disturbances of eye movements in patients with autoimmune diseases and suspected neuropsychiatric involvement

Although a wide range of diagnostic tools have been used to assess CNS involvement in autoimmune disease, no single technique has proven to be reliable. Patients with these diseases often underwent detailed neurocognitive test batteries which are extremely time consuming and quite expensive. The cognitive deficits of these individuals are sometimes unspecific. Nevertheless, patients suffering from intracerebral affection of autoimmune diseases are extremely handicapped in their daily activities and work. These diseases are often associated with a depressive syndrome in many cases resistant to therapeutic efforts. Psychiatric treatment is not infrequent and the clinical picture is dominated by impaired intellectual performance, poor concentration, mental fatigue and depression, often related to emotional stress. For these reasons cognitive deficits in individuals being suspected for neuropsychiatric symptoms in autoimmune diseases are often misdiagnosed. Imaging techniques like MRI and CT only sometimes show pathological results. Electroencephalography (EEG) is not specific for the disease and adds little to diagnosis. Even the positron emission tomography (PET) does not always reveal pathological findings. With the aid of the non-invasive eye movement measurement technique it is possible to detect eye movement disturbances in individuals being suspected for intracerebral affection with autoimmune diseases. 10 patients (5 with SLE, 5 with other autoimmune diseases) and 10 healthy controls were examined using infrared oculography to measure disturbances of eye movements in order to determine whether this method is useful in the assessment of CNS involvement. For smooth pursuit eye movements (SPEM) there was a significantly higher number of correction saccades (p <0.01) and a non-significant trend towards a fixation deficit in patients compared to controls.

Eye movements in a simple spatial reasoning task.

We report two experiments in which participants read a question about the spatial relationship between two letters, then viewed a visual display containing the letters and were required to respond to the question. The format of the question influenced the nature of the eye movements generated to the visual display. Participants also had a tendency to make additional eye movements in order to generate a fixation sequence that corresponded to the order of the letters in the question. This demonstrates an influence of stored information on eye movement generation, and suggests that the scanpath plays a role in structuring the visual information to facilitate reasoning.

Ocular Movement during Curbside Turns at Intersections

We conducted a driving experiment and measured and analyzed the data on eye movement in order to understand ocular movement during curbside turns at intersections. We used a driving simulator equipped with a system capable of measuring the direction of a subject's glances relative to the heading of their vehicle. By analyzing this data, measured at three intersections, we identified three tasks commonly observed in curbside turns: 1) object inspection; 2) turning; and 3) aligning. During the first task, the measurements showed variable swinging patterns. There was a consistent pattern of looking at targets along the curb in the second task, presumably for guidance while turning the vehicle. During the third task, measurements showed a coherent pattern of returning the glance from turning to the subsequent driving maneuvers.

Oculographic analysis of word reading in hemispatial neglect

Neglect dyslexia is a disorder in which individuals misread text appearing on the contralateral side of space following an acquired lesion, usually to the right parietal lobe. This disorder is generally attributed to an impairment in representing spatial information. To determine whether the spatial representations underlying reading differ from those mediating other forms of visual behavior, we investigated the co-occurrence of neglect dyslexia with that of neglect, which manifests on tasks such as line bisection or line cancellation. We also examined the correlation between neglect dyslexia, when present, and eye movements in order to characterize the neglect dyslexia disorder further. Whereas there is no clear relationship between the reading disorder and other symptoms of visuospatial neglect, suggesting segregated spatial representations, there is a direct correspondence between the oculomotor performance of patients with neglect dyslexia and their reading behavior. This latter result suggests that the reading deficit may well arise from the failure to register and perceive the contralesional information.

"Look where you're going!": gaze behaviour associated with maintaining and changing the direction of locomotion.

In order to fully understand how vision is used to guide locomotion it is necessary to know what people look at as they move through the environment. This study provides information, hitherto lacking, regarding gaze behaviour associated with both maintaining and changing the direction of locomotion: activities that are essential for efficient navigation through our cluttered environment. Participants' spatiotemporal gaze patterns were recorded whilst they performed a task requiring that they either maintained a straight walking trajectory or changed their direction of walking by 30 degrees or 60 degrees, left or right, at the midpoint of a 9-m path. Participants were either visually cued to turn when they stepped on a trigger mat placed one step before the mid-point of the walkway (cued trials) or given verbal instruction about the required route prior to the start of each trial (advance knowledge trials). Our clear finding was that for the large majority of the time participants' gaze was aligned with environmental features lying in their current plane of progression both prior to and following the onset of the transition stride during which the direction change was implemented. This gaze behaviour was observed both during cued trials (78% of total fixation time prior to the transition stride onset and 89% following the transition stride onset) and advance knowledge trials (67% prior to transition stride onset, 92% following transition stride onset). When not aligned with the plane of progression, gaze was normally fixated on environmental features related to either known or potential future routes. Prior to changing the direction of walking, individuals invariably made saccadic eye movements in order to align gaze with the end-point of the required travel path. This gaze realignment was invariably accompanied by head reorientation, which was initiated, on average, at the same time as the saccade. On average, participants fixated gaze on their goal (represented by the cue light at the travel path end-point) until after head realignment with the new path was achieved. Additionally, the head was consistently aligned with participants' current walking direction prior to and following the transition stride even on the minority of occasions when they were looking elsewhere. These findings challenge the ecological validity of existing theories of how visual information is used to determine heading direction and are consistent with the proposal that aligning the head with the desired travel direction through coordinated eye and head movements provides the CNS with an allocentric frame of reference that is used to control the movement of the body in space.