Gaze Changes Research Articles

The superior colliculus projection upon the macaque inferior olive.

Saccade accommodation is a productive model for exploring the role of the cerebellum in behavioral plasticity. In this model, the target is moved during the saccade, gradually inducing a change in the saccade vector as the animal adapts. The climbing fiber pathway from the inferior olive provides a visual error signal generated by the superior colliculus that is believed to be crucial for cerebellar adaptation. However, the primate tecto-olivary pathway has only been explored using large injections of the central portion of the superior colliculus. To provide a more detailed picture, we have made injections of anterograde tracers into various regions of the macaque superior colliculus. As shown previously, large central injections primarily label a dense terminal field within the C subdivision at caudal end of the contralateral medial inferior olive. Several, previously unobserved, sites of sparse terminal labeling were noted: bilaterally in the dorsal cap of Kooy and ipsilaterally in theC subdivision of the medial inferior olive. Small, physiologically directed, injections into the rostral, small saccade portion of the superior colliculus produced terminal fields in the same regions of the medial inferior olive, but with decreased density. Small injections of the caudal superior colliculus, where large amplitude gaze changes are encoded, again labeled a terminal field located in the same areas. The lack of a topographic pattern within the main tecto-olivary projection suggests that either the precise vector of the visual error is not transmitted to the vermis, or that encoding of this error is via non-topographic means.

The Shortest Route is Not Always the Fastest: Probability-Modeled Stereoscopic Eye Movement Completion Time in VR

Speed and consistency of target-shifting play a crucial role in human ability to perform complex tasks. Shifting our gaze between objects of interest quickly and consistently requires changes both in depth and direction. Gaze changes in depth are driven by slow, inconsistent vergence movements which rotate the eyes in opposite directions, while changes in direction are driven by ballistic, consistent movements called saccades , which rotate the eyes in the same direction. In the natural world, most of our eye movements are a combination of both types. While scientific consensus on the nature of saccades exists, vergence and combined movements remain less understood and agreed upon. We eschew the lack of scientific consensus in favor of proposing an operationalized computational model which predicts the completion time of any type of gaze movement during target-shifting in 3D. To this end, we conduct a psychophysical study in a stereo VR environment to collect more than 12,000 gaze movement trials, analyze the temporal distribution of the observed gaze movements, and fit a probabilistic model to the data. We perform a series of objective measurements and user studies to validate the model. The results demonstrate its predictive accuracy, generalization, as well as applications for optimizing visual performance by altering content placement. Lastly, we leverage the model to measure differences in human target-changing time relative to the natural world, as well as suggest scene-aware projection depth. By incorporating the complexities and randomness of human oculomotor control, we hope this research will support new behavior-aware metrics for VR/AR display design, interface layout, and gaze-contingent rendering.

Multilevel Modeling of Gaze From Listeners With Hearing Loss Following a Realistic Conversation.

There is a need for tools to study real-world communication abilities in people with hearing loss. We outline a potential method for this that analyzes gaze and use it to answer the question of when and how much listeners with hearing loss look toward a new talker in a conversation. Twenty-two older adults with hearing loss followed a prerecorded two-person audiovisual conversation in the presence of babble noise. We compared their eye-gaze direction to the conversation in two multilevel logistic regression (MLR) analyses. First, we split the conversation into events classified by the number of active talkers within a turn or a transition, and we tested if these predicted the listener's gaze. Second, we mapped the odds that a listener gazed toward a new talker over time during a conversation transition. We found no evidence that our conversation events predicted changes in the listener's gaze, but the listener's gaze toward the new talker during a silence-transition was predicted by time: The odds of looking at the new talker increased in an s-shaped curve from at least 0.4 s before to 1 s after the onset of the new talker's speech. A comparison of models with different random effects indicated that more variance was explained by differences between individual conversation events than by differences between individual listeners. MLR modeling of eye-gaze during talker transitions is a promising approach to study a listener's perception of realistic conversation. Our experience provides insight to guide future research with this method.

Gaze estimation with semi-supervised eye landmark detection as an auxiliary task

The changes in gaze are often reflected in the movements of eye landmarks, highlighting the relevance of eye landmark learning for accurate gaze estimation. To leverage eye landmarks, we propose a gaze estimation framework that incorporates eye landmark detection as an auxiliary task. However, obtaining eye landmark annotations for real-world gaze datasets is challenging. To address this, we exploit synthetic data, which provides precise eye landmark labels, by jointly training an eye landmark detector using labeled synthetic data and unlabeled real-world data in a semi-supervised manner. To reduce the influence of discrepancy between synthetic and real-world data, we improve the generalization ability of the landmark detector by performing a self-supervised learning strategy on a large scale of unlabeled real-world images. The proposed method outperforms other state-of-the-art gaze estimation methods on three gaze datasets, indicating the effectiveness of leveraging eye landmark detection as an auxiliary task to enhance gaze estimation performance.

Using a video-based eye tracker to analyse the binocular near-reflex dynamics response.

This study presents a novel video-based eye-tracking system for analysing the dynamics of the binocular near-reflex response. The system enables the simultaneous measurement of convergence, divergence and pupillary size during accommodation and disaccommodation to aid the comprehensive understanding of the three-component near-reflex. A high-speed (90 Hz) video-based eye tracker was used to capture changes in eye gaze and pupil radius in 15 participants in response to altering stimulus conditions. An offline analysis involved separating the gaze vector components and pupil radius, which were fitted to a hyperbolic tangent function to characterise the dynamics of the near-reflex process. Significant differences in the temporal parameters of the pupil radius were observed between the near-to-far and far-to-near vision changes, with faster miosis compared with mydriasis. Additionally, differences in response times were found between gaze angle components, with longer convergence times compared to changes in the vertical direction (saccades). The steady-state values of the gaze components and pupil radius were in line with theoretical expectations and previous reports. The proposed system provides a non-invasive, portable and cost-effective method for evaluating near-reflex dynamics under natural viewing conditions using a video-based eye tracker. The sampling rate ensures the accurate assessment of vergence eye movements and pupillary dynamics. By simultaneously measuring eye convergence, divergence and pupil size, the system offers a more comprehensive assessment of the near-reflex response. This makes it a valuable tool for clinical diagnosis, research studies and investigating the effects of near work on the visual system.

Changes in oculo‐motor activity during a cognitive challenge can distinguish clinical stages of early Alzheimer’s disease

AbstractBackgroundThe eye adapts to the demands of our behavior [1], its motor activity has proven to be a feasible method for measuring cognition in both health and disease [2]. This study assessed the sensitivity of oculo‐motor features in a benign cognitive challenge model with the purpose of identifying objective efficacy readouts for clinical drug trials in early Alzheimer’s disease (AD).MethodFifty participants, aged 60 to 80 years, performed a reading task in two sessions conducted the same day, morning and evening (i.e. the “cognitive challenge”), with an average inter‐session period of 9.28h, during which participants were not allowed to take naps or consume stimulating beverages. Participants were distributed across four cohorts corresponding to progressive stages of early AD [3]: 1) amyloid negative, cognitively healthy (control group), 2) amyloid positive pre‐symptomatic AD, 3) Mild Cognitive Impairment (MCI) due to AD (pre‐dementia group) and 4) mild AD (mild‐dementia group). ViewMind technology was used to track the oculo‐motor activity [4].ResultNone of the four cohorts reported increased levels of sleepiness during the challenge. However, cohorts showed significantly different oculo‐motor responses during the cognitive challenge (Table 1). The control group showed evidence of learning effects on the reading during the challenge reflected in no change in pupil size, longer saccades, less fixations and shorter gaze. Within the pre‐symptomatic group, however, a negative impact of the challenge was observed in a decrease in pupil size and increase in fixations. However, some learning effects were nevertheless seen in this cohort, in shorter gaze and longer saccades. In pre‐dementia group the learning effects were lost and participants demonstrated difficulty performing the task reflected in decreased pupil size and longer gaze. Finally, the mild‐AD participants showed an increase in fixations, longer gaze and no change in pupil size indicating a pattern of poor reading performance during the challenge.ConclusionOur preliminary results demonstrate that oculo‐motor activity may reflect changes in cognitive resources induced by a benign challenge in progressive clinical stages of early AD. These promising results support continued investigation into the potential of eye‐tracking during reading as a sensitive and objective measure .

Mobile Eye Tracking during Experimenting with Digital Scaffolding—Gaze Shifts between Augmented Reality and Experiment during Zinc Iodide Electrolysis Set-Up

In this exploratory eye tracking study, gaze behavior during an experiment on electrolysis of a zinc iodide solution has been examined. The experiment is designed according to inquiry-based learning and therefore well suited to students’ self-directed experimenting in science classrooms. Scaffolding by means of stepwise presented digital hints (sequential scaffolds), here by means of augmented reality (AR), supported learners during the experiment. Two succeeding AR-hints were offered. This research focuses on the set-up of the experiment by learners and the change of gaze between the AR-hints and the real experiment. This was investigated by means of mobile eye tracking. For the analysis of the gaze changes, scanpath analyses are used. Areas of Interest-based visualizations such as radial transition graphs and scarf plots are used to compare and detect similar or different gaze behaviors of participants. Results reveal that students first look at the AR-hints, try to memorize the construction and then switch to setting up the experiment. Recurrent changes of gaze between the AR-hints and the experiment hardly, or do not, occur. Furthermore, students who had already set up the experiment correctly with the first hint only use the second hint for evaluating correctness of their own set-up.

Diverse effects of gaze direction on heading perception in humans.

Gaze change can misalign spatial reference frames encoding visual and vestibular signals in cortex, which may affect the heading discrimination. Here, by systematically manipulating the eye-in-head and head-on-body positions to change the gaze direction of subjects, the performance of heading discrimination was tested with visual, vestibular, and combined stimuli in a reaction-time task in which the reaction time is under the control of subjects. We found the gaze change induced substantial biases in perceived heading, increased the threshold of discrimination and reaction time of subjects in all stimulus conditions. For the visual stimulus, the gaze effects were induced by changing the eye-in-world position, and the perceived heading was biased in the opposite direction of gaze. In contrast, the vestibular gaze effects were induced by changing the eye-in-head position, and the perceived heading was biased in the same direction of gaze. Although the bias was reduced when the visual and vestibular stimuli were combined, integration of the 2 signals substantially deviated from predictions of an extended diffusion model that accumulates evidence optimally over time and across sensory modalities. These findings reveal diverse gaze effects on the heading discrimination and emphasize that the transformation of spatial reference frames may underlie the effects.

The impact of emotional facial expressions on reflexive attention depends on the aim of dynamic gaze changes: An ERP study.

The emotional expression and gaze direction of a face are important cues for human social interactions. However, the interplay of these factors and their neural correlates are only partially understood. In the current study, we investigated ERP correlates of gaze and emotion processing following the initial presentation of faces with different emotional expressions (happy, neutral, angry) and an averted or direct gaze direction as well as following a subsequent change in gaze direction that occurred in half of the trials. We focused on the time course and scalp topography of the N170 and EPN components. The N170 amplitude was larger to averted than direct gaze for the initial face presentation and larger to gaze changes from direct to averted than from averted to direct in response to the gaze change. For the EPN component in response to the initial face presentation, we replicate classic effects of emotion, which did not interact with gaze direction. As a major new finding, changes from direct to averted gaze elicited an EPN-like effect when the face showed a happy expression. No such effect was seen for angry expressions. We conclude that happy faces reflexively attract attention when they look at the observer rather than away from the observer. These results for happy expressions are in line with the shared signal hypothesis that posits a better processing of expressions if their approach or avoidance tendency is consistent with gaze direction. However, the shared signal hypothesis is not supported by the present results for angry faces.

Brain Stimulation for Emotion Regulation in Adolescents With Psychiatric Disorders: Study Protocol for a Clinical-Transdiagnostical, Randomized, Triple-Blinded and Sham-Controlled Neurotherapeutic Trial.

BackgroundAnxiety, conduct and depressive disorders represent three highly prevalent psychiatric conditions in adolescents. A shared underpinning of these disorders is a shortcoming in emotion regulation, connected to the functioning of the ventromedial prefrontal cortex. Thus, an intervention able to target the suggested neural correlate seems to be highly desirable, aiming to hinder a maladaptive development of emotion regulation abilities and chronification of associated psychiatric disorders. As transcranial direct current stimulation (tDCS) was repeatedly demonstrated as a safe and non-invasive method to modulate specific brain activity, research is in demand to evaluate neurotherapeutic applications in adolescents with psychiatric disorders.MethodThis transdiagnostic, randomized, triple-blind and sham-controlled clinical neurostimulation trial primary aims to investigate if emotion regulation abilities are increased after tDCS in adolescents with psychiatric disorders. Secondly, disorder-specific changes in the anxiety, depression or conduct disorder will be investigated, as well as changes in quality of life, and cognitive and emotional functioning after tDCS intervention. We will include 108 adolescents with psychiatric disorders, displaying a substantial deficit in emotion regulation. Of these, one third each has to be primarily diagnosed with a depressive, anxiety or conduct disorder, respectively. Participants will be randomized to the experimental group (n = 54) receiving real anodal tDCS, or to the control group (n = 54) receiving sham tDCS. Brain stimulation will be applied for 20 min on five consecutive days twice targeting the ventromedial prefrontal cortex (vmPFC). Changes in emotion regulation, together with changes in disorder-specific clinical symptoms will be recorded by multi-informant psychological ratings. To inspect changes in behavior and gaze, computerized tasks and an eye tracker system will be used. Changes in brain responses to emotional and cognitive stimuli will be examined with three functional magnetic resonance imaging (fMRI) paradigms. In addition, a resting state MRI will be acquired to investigate possible changes in brain connectivity.DiscussionBy investigating “emotion regulation” as transdiagnostic treatment target, this project is oriented toward the Research Domain Criteria framework with a dimensional view on mental illness. The study aims at investigating the potential of tDCS as non-invasive intervention for depressive, anxiety and conduct disorders in adolescents and broadening the scientific foundation for its clinical application.Clinical Trial RegistrationThe study is ongoing and has been registered in the German Registry of Clinical Trials (DRKS-ID: DRKS00025601X) on the 28.06.2021.

Dynamic and Systemic Perspective in Autism Spectrum Disorders: A Change of Gaze in Research Opens to A New Landscape of Needs and Solutions.

The first step for a harmonious bio-psycho-social framework in approaching autism spectrum disorders (ASD) is overcoming the conflict between the biological and the psychosocial perspective. Biological research can provide clues for a correct approach to clinical practice, assuming that it would lead to the conceptualization of a pathogenetic paradigm able to account for epidemiologic and clinical findings. The upward trajectory in ASD prevalence and the systemic involvement of other organs besides the brain suggest that the epigenetic paradigm is the most plausible one. The embryo-fetal period is the crucial window of opportunity for keeping neurodevelopment on the right tracks, suggesting that women’s health in pregnancy should be a priority. Maladaptive molecular pathways beginning in utero, in particular, a vicious circle between the immune response, oxidative stress/mitochondrial dysfunction, and dysbiosis-impact neurodevelopment and brain functioning across the lifespan and are the basis for progressive multisystemic disorders that account for the substantial health loss and the increased mortality in ASD. Therefore, the biological complexity of ASD and its implications for health requires the enhancement of clinical skills on these topics, to achieve an effective multi-disciplinary healthcare model. Well-balanced training courses could be a promising starting point to make a change.

The unique rectus extraocular muscles of cetaceans: Homologies and possible functions.

Each rectus extraocular muscle in cetaceans divides into two portions: a massive palpebral belly that inserts into the deep surface of the eyelids and a smaller scleral belly that inserts onto the eyeball. While the cetacean palpebral insertions have long been recognized, their homologies and functions remain unclear. To compare cetacean rectus EOM insertions with the global and orbital rectus EOM insertions of other mammals we dissected orbital contents of 20 odontocete species, 2 mysticete species and 18 non-cetacean species, both aquatic and terrestrial. Four cetacean species were also examined with magnetic resonance imaging (MRI). All four rectus muscles in cetaceans had well-developed palpebral bellies and insertions. Adjacent palpebral bellies showed varying degrees of fusion, from near independence to near complete fusion. Fusion was most complete towards palpebral insertions and less towards origins. A medial moiety of the superior rectus palpebral belly is likely the levator palpebrae superioris. Smaller but still robust scleral insertions were present on all recti, with the medial rectus (MR) being significantly more muscular than the others. All non-cetacean species examined had recti with distinct global and orbital insertions, the latter generally onto Tenon's capsule. Orbital insertions in pygmy hippopotamus and Florida manatee extended into the deep surfaces of the eyelids, hence qualifying as palpebral insertions. Our results suggest that rectus EOMs of mammals generally have both global and orbital insertions, and that palpebral bellies of cetaceans and other species are modified homologs of the orbital insertions. The presence of palpebral insertions in pygmy hippopotamus and absence in other cetartiodactyls suggests an intermediate condition between terrestrial cetartiodactyls and cetaceans. Palpebral insertions in Florida manatee and reports of their presence in some pinnipeds suggest parallel evolution in multiple aquatic lineages. Various functions of cetacean palpebral recti have been proposed, including eyelid dilators, protection during diving and thermogenesis for warming eye and brain. For further insight into their possible functions, we observed eye movements of captive bottlenose dolphins (Tursiops truncatus) at the U.S. National Aquarium. Our observations showed that in addition to rotation of the eyeball the entire surrounding palpebral region also moves during gaze changes. For example during upward gaze the globe not only rotates in supraduction but translates dorsally as well. It appears the rectus palpebral bellies are responsible for flexing the palpebral structures and thus also translating the globe, while the scleral insertions act directly for ocular rotation. Along with frequent non-conjugate eye movements, the oculomotor mechanics and repertoire of cetaceans are thus quite distinctive. Summarily, axial displacement within the orbit is a major 'eye movement' in cetaceans, with protrusion and retraction mediated by well-developed circular muscles and retractor bulbi respectively. Torsional eye movements driven by elaborate oblique EOMs are likewise significant. The roles of rectus EOMs for ocular rotation via their scleral insertions, especially the highly muscular MR, are for typical supra/infraductions and nasal/temporal ductions. The palpebral bellies accentuate these ductions by translating the globe and surrounding structures in the same direction.

Find the silver lining or ignore the cloud? Cognitive reappraisal versus visual attention training.

This study contrasted the efficacy of two strategies for emotion regulation, cognitive reappraisal (CR) and attentional control (AC), while using eye-tracking to examine gaze fixation patterns associated with each strategy. Participants (n = 98 undergraduates) viewed emotionally negative and neutral slides before and after one of three training conditions: CR training (verbal instructions to reframe interpretations of negative images), AC training (gaze-contingent feedback emphasizing fixation away from negative portions of images), or a no-training control condition. CR training led to the most beneficial consequences for self-reported emotion ratings; AC training improved emotion ratings more than the no-training control but not as much as CR. AC training led to significantly reduced time fixating gaze on negative content, whereas CR did not alter gaze fixations compared with the no-training control. Moreover, among the AC group, participants who looked away from negative content to a greater extent reported more beneficial change in emotional self-report, whereas that same pattern was not evident in the CR or no-training group. The findings add to evidence that CR training is more effective than distraction-related strategies and that CR does not necessitate gaze changes to be effective. Together, the findings contribute to furthering knowledge about distinct cognitive mechanisms involved in different strategies of emotion regulation. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Vertical saccadic palsy and foveal retinal thinning in Niemann-Pick disease type C.

IntroductionNiemann-Pick type C (NPC) is a lysosomal storage disease that is progressive and life-limiting, with an estimated incidence of 1:120,000 live births. In addition to systemic manifestation with (hepato-)splenomegaly, there are a number of neurological manifestations (ataxia, dysarthria, dementia, cataplexy, epileptic seizures, and psychiatric disorders). Characteristic is vertical supranuclear gaze palsy, which is often overlooked. Early diagnosis and start of therapy improve quality of life. This study aimed to characterize oculomotor dysfunction of NPC patients, and to provide ophthalmologic data including retinal imaging.MethodsEighteen patients with biochemically or genetically diagnosed NPC completed oculomotor and ophthalmologic examination. Ten of them performed saccadometry by infrared based video-oculography. Saccadic parameters were compared to 100 healthy controls, and were correlated with clinical variables. Another subgroup of eight patients received optical coherence tomography (OCT) of the optic disc and the macula, of which the segmented layers were analysed using a crude linear mixed model, and one adjusted for age, sex, and spherical equivalent.ResultsSaccadometry revealed slowed peak velocity compared to controls most evident vertically. Peak velocity correlated negatively with SARA-Score, but correlation with clinical assessment of saccades was not significant. Clinical features in the assessment of vertical saccades were intensive blinking and head movements to initiate gaze changes, and lateral trajectory of the eyes. Macular OCT revealed significant total retinal thinning in the fovea, specifically of the outer nuclear layer and outer retinal layer. Para- and perifoveal retinal thicknesses, as well as peripapillary retinal nerve fibre layer were normal.ConclusionsFoveal thinning was revealed in NPC. It remains to be shown, whether OCT will prove to be useful to monitor progression. Saccadic impairment reflects CNS involvement and therefore is a parameter to demonstrate the progression of NPC, and potentially also the efficacy of new therapies. Saccadometry, in contrast to clinical investigation, allows the precise evaluation of saccades.

How Does Wearing a Facecover Influence the Eye Movement Pattern in Times of COVID-19?

BackgroundSince the emergence of the COVID-19 pandemic facecovers have become a common sight. The effect of facecovers on the gaze when looking at faces has not been assessed yet.ObjectiveThe aim of the present study is to investigate a potential difference in eye movement pattern in observes which are exposed to images showing a face without and with facecover to identify if there is truly a change of gaze when identifying (masked) facial features.Materials and MethodsThe eye movement of a total of 64 study participants (28 males and 36 females) with a mean age of 31.84±9.0 years was analyzed in this cross-sectional observational study. Eye movement analysis was conducted based on positional changes of eye features within an x- and y- coordinate system while two images (face without/with facecover) were displayed for 8 seconds.ResultsThe results of this study revealed that the sequence of focussing on facial regions was not altered when wearing a facecover and followed the sequence: perioral, nose, periorbital. Wearing a facecover significantly increased the time of focussing on the periorbital region and increased also the number of repeated eye fixations during the interval of visual stimulus presentation. No statistically significant differences were observed between male and female participants in their eye movement pattern across all investigated variables with p > 0.433.ConclusionAesthetic practitioners could utilized the presented data and develop marketing and treatment strategies which majorly target the periorbital area understanding the altered eye movement pattern in times of COVID-19.

Novel Time-Delay Side-Collision Warning Model at Non-Signalized Intersections Based on Vehicle-to-Infrastructure Communication.

In complex traffic environments, collision warning systems that rely only on in-vehicle sensors are limited in accuracy and range. Vehicle-to-infrastructure (V2I) communication systems, however, offer more robust information exchange, and thus, warnings. In this study, V2I was used to analyze side-collision warning models at non-signalized intersections: A novel time-delay side-collision warning model was developed according to the motion compensation principle. This novel time-delay model was compared with and verified against a traditional side-collision warning model. Using a V2I-oriented simulated driving platform, three vehicle-vehicle collision scenarios were designed at non-signalized intersections. Twenty participants were recruited to conduct simulated driving experiments to test and verify the performance of each collision warning model. The results showed that compared with no warning system, both side-collision warning models reduced the proportion of vehicle collisions. In terms of efficacy, the traditional model generated an effective warning in 84.2% of cases, while the novel time-delay model generated an effective warning in 90.2%. In terms of response time and conflict time difference, the traditional model gave a longer response time of 0.91 s (that of the time-delay model is 0.78 s), but the time-delay model reduced the driving risk with a larger conflict time difference. Based on an analysis of driver gaze change post-warning, the statistical results showed that the proportion of effective gaze changes reached 84.3%. Based on subjective evaluations, drivers reported a higher degree of acceptance of the time-delay model. Therefore, the time-delay side-collision warning model for non-signalized intersections proposed herein can improve the applicability and efficacy of warning systems in such complex traffic environments and provide reference for safety applications in V2I systems.

Cerebellar projections to the macaque midbrain tegmentum: Possible near response connections.

Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger-Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.

Minimum energy optimal external torque control of human binocular vision

In this paper, we consider eyes from the human binocular system, that simultaneously gaze on stationary point targets in space, while optimally skipping from one target to the next, by rotating their individual gaze directions. The head is assumed fixed on the torso and the rotating gaze directions of the two eyes are assumed restricted to pass through a point in the visual space. It is further assumed that, individually the rotations of the two eyes satisfy the well known Listing’s law. We formulate and study a combined optimal gaze rotation for the two eyes, by constructing a single Riemannian metric, on the associated parameter space. The goal is to optimally rotate so that the convergent gaze changes between two pre-specified target points in a finite time interval [0, 1]. The cost function we choose is the total energy, measured by the L^2 norm, of the six external torques on the binocular system. The torque functions are synthesized by solving an associated ‘two-point boundary value problem’. The paper demonstrates, via simulation, the shape of the optimal gaze trajectory of the focused point of the binocular system. The Euclidean distance between the initial and the final point is compared to the arc-length of the optimal trajectory. The consumed energy, is computed for different eye movement chores and discussed in the paper. Via simulation we observe that certain eye movement maneuvers are energy efficient and demonstrate that the optimal external torque is a linear function in time. We also explore and conclude that splitting an arbitrary optimal eye movement into optimal vergence and version components is not energy efficient although this is how the human oculomotor control seems to operate. Optimal gaze trajectories and optimal external torque functions reported in this paper is new.

Keep your head down: Maintaining gait stability in challenging conditions.

Peripheral vision often deteriorates with age, disrupting our ability to maintain normal locomotion. Laboratory based studies have shown that lower visual field loss, in particular, is associated with changes in gaze and gait behaviour whilst walking and this, in turn, increases the risk of falling in the elderly. Separately, gaze and gait behaviours change and fall risk increases when walking over complex surfaces. It seems probable, but has not yet been established, that these challenges to stability interact. How does loss of the lower visual field affect gaze and gait behaviour whilst walking on a variety of complex surfaces outside of the laboratory? Specifically, is there a synergistic interaction between the effects on behaviour of blocking the lower visual field and increased surface complexity? We compared how full vision versus simulated lower visual field loss affected a diverse range of behavioural measures (head pitch angle, eye angle, muscle coactivation, gait speed and walking smoothness as measured by harmonic ratios) in young participants. Participants walked over a range of surfaces of different complexity, including pavements, grass, steps and pebbles. In both full vision and blocked lower visual field conditions, surface complexity influenced gaze and gait behaviour. For example, more complex surfaces were shown to be associated with lowered head pitch angles, increased leg muscle coactivation, reduced gait speed and decreased walking smoothness. Relative to full vision, blocking the lower visual field caused a lowering of head pitch, especially for more complex surfaces. However, crucially, muscle coactivation, gait speed and walking smoothness did not show a significant change between full vision and blocked lower visual field conditions. Finally, head pitch angle, muscle coactivation, gait speed and walking smoothness were all correlated highly with each other. Our study showed that blocking the lower visual field did not significantly change muscle coactivation, gait speed or walking smoothness. This suggests that young people cope well when walking with a blocked lower visual field, making minimal behavioural changes. Surface complexity had a greater effect on gaze and gait behaviour than blocking the lower visual field. Finally, head pitch angle was the only measure that showed a significant synergistic interaction between surface complexity and blocking the lower visual field. Together our results indicate that, first, a range of changes occur across the body when people walk over more complex surfaces and, second, that a relatively simple behavioural change (to gaze) suffices to maintain normal gait when the lower visual field is blocked, even in more challenging environments. Future research should assess whether young people cope as effectively when several impairments are simulated, representative of the comorbidities found with age.

Where the eyes wander: The relationship between mind wandering and fixation allocation to visually salient and semantically informative static scene content.

Vision is crucial for many everyday activities, but the mind is not always focused on what the eyes see. Mind wandering occurs frequently and is associated with attenuated visual and cognitive processing of external information. Corresponding changes in gaze behavior—namely, fewer, longer, and more dispersed fixations—suggest a shift in how the visual system samples external information. Using three computational models of visual salience and two innovative approaches for measuring semantic informativeness, the current work assessed whether these changes reflect how the visual system prioritizes visually salient and semantically informative scene content, two major determinants in most theoretical frameworks and computational models of gaze control. Findings showed that, in a static scene viewing task, fixations were allocated to scene content that was more visually salient 10 seconds prior to probe-caught, self-reported mind wandering compared to self-reported attentive viewing. The relationship between mind wandering and semantic content was more equivocal, with weaker evidence that fixations are more likely to fall on locally informative scene regions. This indicates that the visual system is still able to discriminate visually salient and semantically informative scene content during mind wandering and may fixate on such information more frequently than during attentive viewing. Theoretical implications are discussed in light of these findings.