Physiology and pathology of eye–head coordination

No robust evidence for an effect of head-movement propensity on central bias in head-constrained scene viewing, despite an effect on fixation duration

When viewing natural scenes, participants tend to direct their gaze towards the image center, the so-called "central bias." Unless the head is fixed, gaze shifts to peripheral targets are accomplished by a combination of eye and head movements, with substantial individual differences in the propensity to use the head. We address the relation of central bias and head-movement propensity. In one part of the experiment, participants viewed natural scenes of two different sizes without moving their head. We found that the central bias of each individual scaled with image size. In another experimental part, the same participants stood in the center of a panoramic screen and shifted their gaze to peripheral targets. Target eccentricities were either instructed by text (endogenous mode) or by a bar appearing at the target location (exogenous mode). In this "peripheral-target" task, we found a strong correlation between the exogenous and the endogenous mode, indicating that they provide a robust measure of an individual's head-movement propensity. Despite substantial inter-individual variability in both tasks, no significant correlation was found between head-movement propensity and central bias, and a trend toward significance for a specific measure was brittle. However, individuals with a higher head-movement propensity tended to have shorter fixation durations in scene viewing. Our results suggest that central bias in free scene viewing on typical screen sizes is predominately determined by visual properties. Although head-movement propensity seems to affect some aspects of scene-viewing behavior (fixation durations), individual differences in central bias are not explained by head-movement propensity.

Efficient gaze stabilization during video Active Gaze Shift Test (vAGST) in bilateral vestibulopathy

Introduction

While most head movements in daily life are active, most tools used to assess vestibular deficits rely on passive head movements. A single gain value is not sufficient to quantify gaze stabilization efficiency during active movements in vestibular deficit patients. Moreover, during active gaze shifts, anticipatory mechanisms come into play. Our aim was to explore the extent to which previously described compensatory mechanisms are employed in patients with bilateral vestibular loss.

Methods

We used a Video Head Impulse Test (vHIT) to simultaneously record eye and head movements during a video Active Gaze Shift Test (vAGST). Thirty-eight patients with bilateral vestibular deficits and 61 control subjects were tested.

Results

Despite impaired performance on caloric tests and vHIT, most patients exhibited normal gaze stabilization (gain = 0.92 ± 0.1) during active gaze shifts up to a head speed ('stall speed') of approximately 140 ± 60°/sec, compared to 280 ± 65°/sec in controls. Our results indicate that BVD patients spontaneously adopt a head speed during active horizontal movements that significantly improves gaze stabilization compared to passive movements. The stall speed correlates with the spontaneous head speed typically adopted by BVD patients and controls in daily activities. As a consequence of the reduction in head speed and corrective saccades, patients also showed an increased delay in gaze stabilization (413 ± 105 ms in BVD patients versus 358 ± 82 ms in controls) at the end of the gaze shift, which might become disabling for certain tasks.

Discussion

Recent model suggests that compensatory eye movements, which stabilize gaze during the counter rotation phase of active gaze shifts, are predictive in nature. vAGST is not designed to provide an etiological diagnosis but rather a functional assessment of the patient's ability to generate predictive eye movements that compensate for vestibular sensor deficits. Understanding the quality of the patient's sensory predictions can also shed light on vestibular symptoms, even in cases where no vestibular sensor deficit is detected. This suggest that quality of life and oscillopsia questionnaires should distinguish between predictable and unpredictable movements.

Sex differences in cervical disc height and neck muscle activation during manipulation of external load from helmets

Neck pain associated with helmet-wear is an occupational health problem often observed in helicopter pilots and aircrew. Whether aircrew helmet wearing is associated with physiological and biomechanical differences between sexes is currently unknown. This study investigated neuromuscular activation patterns during different helmet-wearing conditions. The helmet load was manipulated through a novel Helmet Balancing System (HBS) in healthy, non-pilot male and female participants (n = 10 each, age 19-45 years) in two phases. Phase A assessed the acute effects of helmet-wear on neck muscles activation during head movements. Phase B examined changes in muscle activity and cervical disc height after wearing a helmet for 45 min. In Phase A, muscle activity was similar between sexes in many movements, but it was higher in female participants when wearing a helmet than in males. The HBS reduced muscle activity in both sexes. In Phase B, female participants exhibited a greater level of muscular fatigue, and male participants' cervical disc height was significantly decreased [5.7 (1.4) vs. 4.4 (1.5) mm, P < 0.001] after continuous wearing. Both sexes showed no significant change in muscle fatigue and disc height [male: 5.0 (1.3) vs. 5.2 (1.4) mm, P = 0.604] after applying HBS. These findings demonstrate sex-specific physiological and biomechanical responses to wearing a helmet. They may indicate different postural and motor control strategies, associated with different neck pain aetiologies in male and female aircrew, the knowledge of which is important to reduce or prevent musculoskeletal injuries associated with helmet wearing.

How do referees visually explore? An in-situ examination of the referential head and eye movements of football referees

The majority of a football referee's time is spent assessing open-play situations, yet little is known about how referees search for information during this uninterrupted play. The aim of the current study was to examine the exploratory gaze behaviour of elite and sub-elite football referees in open-play game situations. Four elite (i.e. national) and eight sub-elite (i.e. regional) referees officiated an in-situ football match while wearing a mobile eye-tracker to assess their gaze behaviour. Both referential head and eye movements (i.e. moving gaze away from and then back to the ball) were measured. Results showed gaze behaviour was characterised overall by more referential head than eye movements (~75 vs 25%), which were of longer duration (~950 vs 460 ms). Moreover, elite referees employed faster referential movements (~640 vs 730 ms), spending less time with their gaze away from the ball (carrier) than the sub-elite referees. Crucially, both the referential head and eye movements were coordinated relative to key events in the match, in this case passes, showing that referees anticipate the passes to ensure that the referential movements did not occur during passes, rather before or after. The results further our understanding of the coordinative gaze behaviours that underpin expertise in officiating.

Benefits associated with the standing position during visual search tasks

The literature on postural control highlights that task performance should be worse in challenging dual tasks than in a single task, because the brain has limited attentional resources. Instead, in the context of visual tasks, we assumed that (i) performance in a visual search task should be better when standing than when sitting and (ii) when standing, postural control should be better when searching than performing the control task. 32 and 16 young adults participated in studies 1 and 2, respectively. They performed three visual tasks (searching to locate targets, free-viewing and fixating a stationary cross) displayed in small images (visual angle: 22°) either when standing or when sitting. Task performance, eye, head, upper back, lower back and center of pressure displacements were recorded. In both studies, task performance in searching was as good (and clearly not worse) when standing as when sitting. Sway magnitude was smaller during the search task (vs. other tasks) when standing but not when sitting. Hence, only when standing, postural control was adapted to perform the challenging search task. When exploring images, and especially so in the search task, participants rotated their head instead of their eyes as if they used an eye-centered strategy. Remarkably in Study 2, head rotation was greater when sitting than when standing. Overall, we consider that variability in postural control was not detrimental but instead useful to facilitate visual task performance. When sitting, this variability may be lacking, thus requiring compensatory movements.

The Role of Neck Input in Producing Corrective Saccades in the Head Impulse Test

Background

The head impulse test is a valuable clinical test that can help identify peripheral vestibular dysfunction by observing corrective saccades that return the eyes to the target of interest. Corrective saccades have been classified as covert if the onset occurs before the end of the head impulse and as overt if they occur afterwards. However, the mechanism that trigger these saccades remain unclear.

Objective

The objective of this study was to examine the role of neck input in generating overt as well as covert saccades.

Methods

Sixteen patients (9 males and 7 females: age 35-80 years, average 62.7 years old) who showed corrective saccades during the head impulse test were included. Twelve patients had unilateral vestibular dysfunction, and 4 patients had bilateral vestibular dysfunction. Patients underwent both the head impulse test (HIT) and the body impulse test (BIT) in a randomized order. While the head is rotated horizontally in HIT, the body is rotated horizontally in BIT. During BIT, the neck is fixed by a cervical collar (neck lock extrication collar) to reduce somatosensory input from the neck. The head movements and eye movements were recorded and analyzed by the video HIT recording system.

Results

In all 16 patients, corrective saccades were observed in HIT as well as in BIT. While there were no significant differences in peak head velocities between HIT and BIT (p = 0.33, paired t-test), the VOR gain in BIT was significantly smaller than that in HIT (p = 0.011, paired t-test). The number of overt saccades per trial in BIT was significantly decreased compared to that in HIT (p < 0.001, paired t-test) whereas there were no significant differences in the number of covert saccades between the two tests. The proportion of overt saccades among all corrective saccades in BIT was significantly lower than the proportion in HIT (p < 0.001, paired t-test).

Conclusions

Somatosensory input from the neck contributes to the generation of overt saccades and reinforces the vestibulo-ocular reflex complementing the retinal slip during high frequency head movements.

Trunk and head displacements stabilized to perform both horizontal and vertical saccadic eye movements

Vision is crucial for humans to interact with their surrounding environment, and postural sway is reduced to allow short eye movements. However, the extent of subtle changes in postural control for horizontal and vertical eye movements remains unclear. The goal of this study was to investigate the effects of vertical and horizontal eye movements on head and trunk control in young adults. Fifteen healthy adults (23.4 ± 4.7 years) stood upright in three conditions for 60 s: fixation, horizontal, and vertical guided eye movements. In fixation, participants had to fixate on a stationary target. In both the horizontal and vertical eye movements, the target was presented with a frequency of 0.5 Hz and a visual angle of 11°. Eye displacement was monitored using a SMI eye tracker (ETG2.0) and trunk and head sway were monitored using infrared markers (Optotrak 3020, NDI). The mean sway amplitude was lower in both directions for eye movements and lowest in the vertical direction compared to the fixation condition. The sway area was also lower in vertical eye movement than in the fixation condition. We also found that the sway reduction was greater at head than at trunk level. The median frequency sway in the anterior-posterior direction was higher in both eye movements than in fixation. Based upon these results, we suggest that to perform short eye movements, postural sway is more strongly controlled at the head level than at the trunk and in vertical eye movements than in horizontal movements.

Saccadic eye movement performance reduces visual manipulation influence and center of pressure displacements in older fallers

This study examined changes in postural control and gaze performance of faller and non-faller older adults under conditions of visual tasks and optical flow manipulations. Fifteen older non-fallers (69.8 years, ± 3.2) and fifteen older fallers (71.1 years, ± 6.4) stood on a force platform inside a moving room wearing an eye tracker. Four tasks were performed: gaze fixation; predictable saccades; unpredictable saccades; and free-viewing. The stimuli appeared at a frequency of 1.1 Hz during conditions of predictable and unpredictable saccades. Sixteen trials were divided into two blocks. In the first block, the room remained stationary. In the second block, the room oscillated, without the participant's awareness, with a 0.6 cm amplitude and 0.2 Hz frequency. Results showed postural sway attenuation in older fallers during the saccadic tasks compared to gaze fixation and free-viewing tasks, in both stationary and moving room conditions. Both groups showed increased center of pressure (CoP) magnitude during the moving room condition and CoP displacements strongly coupled to the room's movement. The influence of the moving room on the postural sway was reduced during the saccadic tasks for both older groups. Older fallers exhibited higher variability compared to older non-fallers. Gaze behavior differences between groups were dependent on the goals of the visual tasks. Therefore, CoP displacements of older adults are reduced during saccadic tasks regardless of their falling history. However, postural and gaze performance of older fallers suggests increased deterioration of postural and oculomotor control which may be used as a predictor of fall risk.

Head and eyes: Looking behavior in 12- to 24-month-old infants

This study demonstrates evidence for a foundational process underlying active vision in older infants during object play. Using head-mounted eye-tracking and motion capture, looks to an object are shown to be tightly linked to and synchronous with a stilled head, regardless of the duration of gaze, for infants 12 to 24 months of age. Despite being a developmental period of rapid and marked changes in motor abilities, the dynamic coordination of head stabilization and sustained gaze to a visual target is developmentally invariant during the examined age range. The findings indicate that looking with an aligned head and eyes is a fundamental property of human vision and highlights the importance of studying looking behavior in freely moving perceivers in everyday contexts, opening new questions about the role of body movement in both typical and atypical development of visual attention.

Evaluating the Effects of In-Vehicle Side-View Display Layout Design on Physical Demands of Driving

OBJECTIVE

A driving simulator study was conducted to comparatively evaluate the effects of three camera monitor system (CMS) display layouts and the traditional side-view mirror arrangement on the physical demands of driving.

BACKGROUND

Despite the possible benefits of CMS displays in reducing the physical demands of driving, little empirical evidence is available to substantiate these benefits. The effects of CMS display layout designs are not well understood.

METHOD

The three CMS display layouts varied in the locations of the side-view displays: (A) inside the car near the conventional side-view mirrors, (B) on the dashboard at each side of the steering wheel, and (C) on the center fascia with the displays joined side by side. Twenty-two participants performed a safety-critical lane changing task with each design alternative. The dependent measures were the following: spread of eye movement, spread of head movement, and perceived physical demand.

RESULTS

Compared with the traditional mirror system, all three CMS display layouts showed a reduction in physical demands, albeit differing in the types/magnitudes of physical demand reduction.

CONCLUSION

Well-designed CMS display layouts could significantly reduce the physical demands of driving. The physical demands were reduced by placing the CMS displays close to the position of the driver's normal line-of-sight when looking at the road ahead and locating each CMS display on each side of the driver, that is, at locations compatible with the driver's expectation.

APPLICATION

Physical demand reductions by CMS displays would especially benefit drivers frequently checking the side-view mirrors with large eye/head movements and physically weak/impaired drivers.

Comparative Analysis of Kinect-Based and Oculus-Based Gaze Region Estimation Methods in a Driving Simulator

Driver's gaze information can be crucial in driving research because of its relation to driver attention. Particularly, the inclusion of gaze data in driving simulators broadens the scope of research studies as they can relate drivers' gaze patterns to their features and performance. In this paper, we present two gaze region estimation modules integrated in a driving simulator. One uses the 3D Kinect device and another uses the virtual reality Oculus Rift device. The modules are able to detect the region, out of seven in which the driving scene was divided, where a driver is gazing at in every route processed frame. Four methods were implemented and compared for gaze estimation, which learn the relation between gaze displacement and head movement. Two are simpler and based on points that try to capture this relation and two are based on classifiers such as MLP and SVM. Experiments were carried out with 12 users that drove on the same scenario twice, each one with a different visualization display, first with a big screen and later with Oculus Rift. On the whole, Oculus Rift outperformed Kinect as the best hardware for gaze estimation. The Oculus-based gaze region estimation method with the highest performance achieved an accuracy of 97.94%. The information provided by the Oculus Rift module enriches the driving simulator data and makes it possible a multimodal driving performance analysis apart from the immersion and realism obtained with the virtual reality experience provided by Oculus.

A pilot study on the evaluation of eye, head, and trunk coordination in subjects with chronic whiplash during a target-tracking task - A driving context approach

BACKGROUND

Motor vehicle accidents (MVA) are the most common causes of whiplash injuries. Difficulties with driving and changes in driving behavior are reported by subjects with chronic whiplash associated disorders (WAD). Proper eye and head coordination is required for driving tasks. Disturbances of eye and head coordination were found in these subjects with chronic WAD.

OBJECTIVES

The objective of this pilot study is to evaluate eye, head and trunk coordination in subjects with chronic WAD due to MVA and healthy controls during a target-tracking task using a functionally oriented approach in the context of driving.

DESIGN

Cross-sectional.

METHOD

The subjects performed target tracking tasks that reproduced eye and head movements required while driving. Head and trunk motion was captured using a motion capture system and eye movement was captured with an eye-tracker. Response time, time to target, and eye, head, and trunk contribution of movement were measured.

RESULTS/FINDINGS

Subjects with chronic WAD presented delayed response time and time to reach the targets with both eyes and head compared to the control group, and tended to compensate the lack of neck motion with increased eye motion.

CONCLUSIONS

This study shows indications of impairments of eye and head coordination in chronic WAD due to MVA when compared to healthy subjects. These alterations may have implications for driving safety.

Interaction between eye and body movements to perform visual tasks in upright stance

Synergistic interactions between visual and postural behaviors were observed in a previous study during a precise visual task (search for a specific target in a picture) performed upright as steady as possible. The goal of the present study was to confirm and extend these novel findings in a more ecological condition with no steadiness requirement. Twelve healthy young adults performed two visual tasks, i.e. a precise task and a control task (free-viewing). Center of pressure, lower back, neck, head and eye movements were recorded during each task. The subjective cognitive workload was assessed after each task (NASA-TLX questionnaire). Pearson correlations and cross-correlations between eyes (time-series, characteristics of fixation) and center of pressure/body movements were used to test the synergistic model. As expected, significant negative Pearson correlations between eye and head-neck movement variables were only observed in searching. They indicated that larger precise gaze shifts were correlated with lower head and neck movements. One cross-correlation coefficient (between COP on the AP axis and eyes in the up/down direction) was also significantly higher, i.e. stronger, in searching than in free-viewing. These synergistic interactions likely required greater cognitive demand as indicated by the greater NASA-TLX score in searching. Moreover, the previous Pearson correlations were no longer significant after controlling for the NASA-TLX global score (thanks to partial correlations). This study provides new evidence of the existence of a synergistic process between visual and postural behaviors during visual search tasks.

Semi tandem base of support degrades both saccadic gaze control and postural stability particularly in older adults

Differences in the postural stabilization of older and young adults have been shown to be task-dependent on both visual and postural challenges; however, the gaze behavior during such tasks has rarely been examined. This study investigated the effects of horizontal and vertical saccades on gaze control, center of pressure (CoP) and head displacement of young and older adults on different bases of support. Ten young adults (20.7 ± 3.4 years) and ten older adults (71.6 ± 3.1 years) remained in an upright stance on a force platform wearing an eye-head tracker device. The participants performed 30-second trials according to two bases of support (feet apart and semi-tandem) and three gaze behavior (fixation, horizontal and vertical saccades) conditions. Older adults presented greater CoP amplitude (p < 0.002) and velocity (p < 0.001) (ML axis), and higher head amplitude (ML) (p < 0.002) than young adults during the semi tandem base. Head displacement of both groups presented higher velocity (ML axis) during horizontal (p < 0.001) and vertical saccades (p < 0.01) than the fixation task only on the semi tandem base. There was higher number of fixations (p < 0.001) and lower mean fixation duration (p < 0.001) on the semi-tandem base (p < 0.05). The results showed higher gaze latency variability in vertical saccades for older adults (p < 0.01). Challenging postural tasks may alter postural adjustments and gaze control during saccadic tasks. Particularly, the greater postural instability of older adults increased the gaze latency variability during saccadic tasks, suggesting some deterioration in the posture-gaze relation with aging.

Residual vision activation and the brain-eye-vascular triad: Dysregulation, plasticity and restoration in low vision and blindness - a review

Vision loss due to ocular diseases such as glaucoma, optic neuropathy, macular degeneration, or diabetic retinopathy, are generally considered an exclusive affair of the retina and/or optic nerve. However, the brain, through multiple indirect influences, has also a major impact on functional visual impairment. Such indirect influences include intracerebral pressure, eye movements, top-down modulation (attention, cognition), and emotionally triggered stress hormone release affecting blood vessel dysregulation. Therefore, vision loss should be viewed as the result of multiple interactions within a “brain-eye-vascular triad”, and several eye diseases may also be considered as brain diseases in disguise. While the brain is part of the problem, it can also be part of the solution. Neuronal networks of the brain can “amplify” residual vision through neuroplasticity changes of local and global functional connectivity by activating, modulating and strengthening residual visual signals. The activation of residual vision can be achieved by different means such as vision restoration training, non-invasive brain stimulation, or blood flow enhancing medications. Modulating brain functional networks and improving vascular regulation may offer new opportunities to recover or restore low vision by increasing visual field size, visual acuity and overall functional vision. Hence, neuroscience offers new insights to better understand vision loss, and modulating brain and vascular function is a promising source for new opportunities to activate residual vision to achieve restoration and recovery to improve quality of live in patients suffering from low vision.

Optic Nerve Sheath Tethering in Adduction Occurs in Esotropia and Hypertropia, But Not in Exotropia

Purpose

Repetitive strain to the optic nerve (ON) due to tethering in adduction has been recently proposed as an intraocular pressure-independent mechanism of optic neuropathy in primary open-angle glaucoma. Since strabismus may alter adduction, we investigated whether gaze-related ON straightening and associated globe translation differ in horizontal and vertical strabismus.

Methods

High-resolution orbital magnetic resonance imaging was obtained in 2-mm thick quasi-coronal planes using surface coils in 25 subjects (49 orbits) with esotropia (ET, 19 ± 3.6Δ SEM), 11 (15 orbits) with exotropia (XT, 33.7 ± 7.3Δ), 7 (12 orbits) with hypertropia (HT, 14.6 ± 3.2Δ), and 31 normal controls (62 orbits) in target-controlled central gaze, and in maximum attainable abduction and adduction. Area centroids were used to determine ON path sinuosity and globe positions.

Results

Adduction angles achieved in ET (30.6° ± 0.9°) and HT (27.2° ± 2.3°) did not significantly differ from normal (28.3° ± 0.7°), but significantly less adduction was achieved in XT (19.0° ± 2.5°, P = 0.005). ON sheath tethering in adduction occurred in ET and HT similarly to normal, but did not in XT. The globe translated significantly less than normal, nasally in adduction in XT and temporally in abduction in ET and HT (P < 0.02, for all). Globe retraction did not occur during abduction or adduction in any group.

Conclusions

Similar to normal subjects, the ON and sheath become tethered without globe retraction in ET and HT. In XT, adduction tethering does not occur, possibly due to limited adduction angle. Thus, therapeutic limitation of adduction could be considered as a possible treatment for ON sheath tethering.

Referential processing during reading: concurrent recordings of eye movements and head motion

The present study utilized a new experimental set-up synchronizing eye movements and head motion for investigating referential change occurring in a reading task. We examined the effects of a change in narrative perspective during reading on eye movements and head motion. Forty-four participants read texts on a digital tablet, and both participants' eye movements and head movements were recorded using eye tracker and motion capture. The results showed longer eye fixation duration, longer reading time and decreasing head motions when perspective changed. Recent studies have supported the dynamic engagement hypothesis suggesting that there is a fluctuation in cognitive engagement reflected by postural movements. Our findings on head movements seem to validate this hypothesis of a bodily engagement in reading. The results provided by our study showed that the novel methodology of eye and head movement recordings we used was proven to be informative in studying the reader's embodiment during reading.

Automatic and intentional influences on saccade landing

Saccadic eye movements enable us to rapidly direct our high-resolution fovea onto relevant parts of the visual world. However, while we can intentionally select a location as a saccade target, the wider visual scene also influences our executed movements. In the presence of multiple objects, eye movements may be "captured" to the location of a distractor object, or be biased toward the intermediate position between objects (the "global effect"). Here we examined how the relative strengths of the global effect and visual object capture changed with saccade latency, the separation between visual items and stimulus contrast. Importantly, while many previous studies have omitted giving observers explicit instructions, we instructed participants to either saccade to a specified target object or to the midpoint between two stimuli. This allowed us to examine how their explicit movement goal influenced the likelihood that their saccades terminated at either the target, distractor, or intermediate locations. Using a probabilistic mixture model, we found evidence that both visual object capture and the global effect co-occurred at short latencies and declined as latency increased. As object separation increased, capture came to dominate the landing positions of fast saccades, with reduced global effect. Using the mixture model fits, we dissociated the proportion of unavoidably captured saccades to each location from those intentionally directed to the task goal. From this we could extract the time course of competition between automatic capture and intentional targeting. We show that task instructions substantially altered the distribution of saccade landing points, even at the shortest latencies.NEW & NOTEWORTHY When making an eye movement to a target location, the presence of a nearby distractor can cause the saccade to unintentionally terminate at the distractor itself or the average position in between stimuli. With probabilistic mixture models, we quantified how both unavoidable capture and goal-directed targeting were influenced by changing the task and the target-distractor separation. Using this novel technique, we could extract the time course over which automatic and intentional processes compete for control of saccades.

Workflows and individual differences during visually guided routine tasks in a road traffic management control room

Road traffic control rooms rely on human operators to monitor and interact with information presented on multiple displays. Past studies have found inconsistent use of available visual information sources in such settings across different domains. In this study, we aimed to broaden the understanding of observer behaviour in control rooms by analysing a case study in road traffic control. We conducted a field study in a live road traffic control room where five operators responded to incidents while wearing a mobile eye tracker. Using qualitative and quantitative approaches, we investigated the operators' workflow using ergonomics methods and quantified visual information sampling. We found that individuals showed differing preferences for viewing modalities and weighting of task components, with a strong coupling between eye and head movement. For the quantitative analysis of the eye tracking data, we propose a number of metrics which may prove useful to compare visual sampling behaviour across domains in future.

A genome-wide screen for acrophobia susceptibility loci in a Finnish isolate

Acrophobia, an abnormal fear of heights, is a specific phobia characterized as apprehension cued by the occurrence or anticipation of elevated spaces. It is considered a complex trait with onset influenced by both genetic and environmental factors. Identification of genetic risk variants would provide novel insight into the genetic basis of the fear of heights phenotype and contribute to the molecular-level understanding of its aetiology. Genetic isolates may facilitate identification of susceptibility alleles due to reduced genetic heterogeneity. We took advantage of an internal genetic isolate in Finland in which a distinct acrophobia phenotype appears to be segregating in pedigrees originally ascertained for schizophrenia. We conducted parametric, nonparametric, joint linkage and linkage disequilibrium analyses using a microsatellite marker panel, genotyped in families to search for chromosomal regions correlated with acrophobia. Our results implicated a few regions with suggestive evidence for linkage on chromosomes 4q28 (LOD = 2.17), 8q24 (LOD = 2.09) and 13q21-q22 (LOD = 2.22). We observed no risk haplotypes shared between different families. These results suggest that genetic predisposition to acrophobia in this genetic isolate is unlikely to be mediated by a small number of shared high-risk alleles, but rather has a complex genetic architecture.

Evaluation of eye, head and trunk coordination during target tracking tasks

This study tested the feasibility of a method to synchronise and to evaluate eye, head and trunk movement patterns during target tracking tasks performed by 10 subjects. A projected central target was randomly repositioned at 40° and 70° of rotation to the left and right. Subjects were instructed to change gaze as quickly as possible. Head and trunk motion was measured using a motion analysis system, and eye movement was measured using an eye-tracker; all data were synchronised. For healthy subjects, the eye moved faster than the head, there was no trunk movement and the head moved more than the eye to reach further displaced targets. The method tested was feasible, and it could be used to evaluate eye, head and trunk movement patterns of subjects with injuries such as whiplash and concussions. Practitioner Summary: Studies of eye, head and trunk movements using synchronised methods are needed. We tested the feasibility of a method to synchronise and evaluate eye, head and trunk movement patterns. The method tested was feasible, and it could be used to evaluate movement patterns of subjects with injuries such as whiplash.

A functional synergistic model to explain postural control during precise visual tasks

In everyday life, individuals sometimes have to perform precise, or challenging, visual tasks in upright standing. Upright, one problem to perform precise saccades and fixations is that the body oscillates continuously in a mainly unpredictable way. Current cognitive models assume that the central nervous system should divide its attention to perform these 'dual tasks' because of limited attentional resources (keeping balance and performing the precise visual task). The problem with the concept of duality is that individuals (need to) succeed in precise visual tasks upright and should not be more unstable and inefficient - because of a division of attention - in these tasks. In our opinion, the central nervous system should work adaptively in a way that enables success in these tasks. Hence, instead of assuming 'duality' in cognitive processes, we suggest that i) a 'synergy' - or unification - between visual and postural processes may be required to succeed in precise visual tasks. Success in precise visual tasks upright would also require ii) the synergy to be based on two feedforward processes with the visual process being the leader; iii) individuals to reduce their postural sway to facilitate successful synergies; iiii) additional cognitive resources to link visual and postural processes. We discuss some literature findings consistent with these assumptions and summarize a recent validation of the synergistic model. In summary, both models of duality and synergy could be complementary and the present manuscript shows how they could be included in a higher-order, two directional, cognitive model of postural control.

Quantifying external focus of attention in sailing by means of action sport cameras

The aim of the current study was twofold: (1) to validate the use of action sport cameras for quantifying focus of visual attention in sailing and (2) to apply this method to examine whether an external focus of attention is associated with better performance in upwind sailing. To test the validity of this novel quantification method, we first calculated the agreement between gaze location measures and head orientation measures in 13 sailors sailing upwind during training regattas using a head mounted eye tracker. The results confirmed that for measuring visual focus of attention in upwind sailing, the agreement for the two measures was high (intraclass correlation coefficient (ICC) = 0.97) and the 95% limits of agreement were acceptable (between -8.0% and 14.6%). In a next step, we quantified the focus of visual attention in sailing upwind as fast as possible by means of an action sport camera. We captured sailing performance, operationalised as boat speed in the direction of the wind, and environmental conditions using a GPS, compass and wind meter. Four trials, each lasting 1 min, were analysed for 15 sailors each, resulting in a total of 30 upwind speed trials on port tack and 30 upwind speed trials on starboard tack. The results revealed that in sailing - within constantly changing environments - the focus of attention is not a significant predictor for better upwind sailing performances. This implicates that neither external nor internal foci of attention was per se correlated with better performances. Rather, relatively large interindividual differences seem to indicate that different visual attention strategies can lead to similar performance outcomes.

Eyelid Opening with Trigeminal Proprioceptive Activation Regulates a Brainstem Arousal Mechanism

Eyelid opening stretches mechanoreceptors in the supratarsal Müller muscle to activate the proprioceptive fiber supplied by the trigeminal mesencephalic nucleus. This proprioception induces reflex contractions of the slow-twitch fibers in the levator palpebrae superioris and frontalis muscles to sustain eyelid and eyebrow positions against gravity. The cell bodies of the trigeminal proprioceptive neurons in the mesencephalon potentially make gap-junctional connections with the locus coeruleus neurons. The locus coeruleus is implicated in arousal and autonomic function. Due to the relationship between arousal, ventromedial prefrontal cortex, and skin conductance, we assessed whether upgaze with trigeminal proprioceptive evocation activates sympathetically innervated sweat glands and the ventromedial prefrontal cortex. Specifically, we examined whether 60° upgaze induces palmar sweating and hemodynamic changes in the prefrontal cortex in 16 subjects. Sweating was monitored using a thumb-mounted perspiration meter, and prefrontal cortex activity was measured with 45-channel, functional near-infrared spectroscopy (fNIRS) and 2-channel NIRS at Fp1 and Fp2. In 16 subjects, palmar sweating was induced by upgaze and decreased in response to downgaze. Upgaze activated the ventromedial prefrontal cortex with an accumulation of integrated concentration changes in deoxyhemoglobin, oxyhemoglobin, and total hemoglobin levels in 12 subjects. Upgaze phasically and degree-dependently increased deoxyhemoglobin level at Fp1 and Fp2, whereas downgaze phasically decreased it in 16 subjects. Unilateral anesthetization of mechanoreceptors in the supratarsal Müller muscle used to significantly reduce trigeminal proprioceptive evocation ipsilaterally impaired the increased deoxyhemoglobin level by 60° upgaze at Fp1 or Fp2 in 6 subjects. We concluded that upgaze with strong trigeminal proprioceptive evocation was sufficient to phasically activate sympathetically innervated sweat glands and appeared to induce rapid oxygen consumption in the ventromedial prefrontal cortex and to rapidly produce deoxyhemoglobin to regulate physiological arousal. Thus, eyelid opening with trigeminal proprioceptive evocation may activate the ventromedial prefrontal cortex via the mesencephalic trigeminal nucleus and locus coeruleus.

Assistive peripheral prosthetic vision aids perception and mobility in outdoor environments: A virtual-reality simulation study

Retinitis pigmentosa (RP) causes visual field (VF) constriction due to progressive loss of photoreceptors, typically from the retinal periphery to the fovea. Retinal prostheses offer vision restoration via electrode implantation and stimulation near the fovea, thereby eliciting articifial percepts, so-called phosphenes in the center VF. Although foveal photoreceptors can persist for prolonged periods of time, bionic therapy is usually restricted to stages of RP with complete vision loss. However, persons with RP experience mobility impairment from peripherally restricted VFs much earlier. Consequently, the amount of visual scanning necessary for navigation is increased, and maintaining a steady pace is challenging. Receiving a retinal implant at this early stage might be feasible. We investigated the potential of a peripheral visual prosthesis coexisting with central residual vision to facilitate scene perception and mobility. Simulating prosthetic and residual vision in a virtual mobility environment, we found that assistive phosphene layouts were associated with reductions in visual scanning-related head movements of up to 42.1%, body rotations of up to 30%, and up to 45% lower frequency of stopping when circumventing low-lying obstacles, pedestrians and following a path. Further research on early implantation of retinal prostheses for the peripheral VF is therefore advised.

Driving with binocular visual field loss? A study on a supervised on-road parcours with simultaneous eye and head tracking

Post-chiasmal visual pathway lesions and glaucomatous optic neuropathy cause binocular visual field defects (VFDs) that may critically interfere with quality of life and driving licensure. The aims of this study were (i) to assess the on-road driving performance of patients suffering from binocular visual field loss using a dual-brake vehicle, and (ii) to investigate the related compensatory mechanisms. A driving instructor, blinded to the participants' diagnosis, rated the driving performance (passed/failed) of ten patients with homonymous visual field defects (HP), including four patients with right (HR) and six patients with left homonymous visual field defects (HL), ten glaucoma patients (GP), and twenty age and gender-related ophthalmologically healthy control subjects (C) during a 40-minute driving task on a pre-specified public on-road parcours. In order to investigate the subjects' visual exploration ability, eye movements were recorded by means of a mobile eye tracker. Two additional cameras were used to monitor the driving scene and record head and shoulder movements. Thus this study is novel as a quantitative assessment of eye movements and an additional evaluation of head and shoulder was performed. Six out of ten HP and four out of ten GP were rated as fit to drive by the driving instructor, despite their binocular visual field loss. Three out of 20 control subjects failed the on-road assessment. The extent of the visual field defect was of minor importance with regard to the driving performance. The site of the homonymous visual field defect (HVFD) critically interfered with the driving ability: all failed HP subjects suffered from left homonymous visual field loss (HL) due to right hemispheric lesions. Patients who failed the driving assessment had mainly difficulties with lane keeping and gap judgment ability. Patients who passed the test displayed different exploration patterns than those who failed. Patients who passed focused longer on the central area of the visual field than patients who failed the test. In addition, patients who passed the test performed more glances towards the area of their visual field defect. In conclusion, our findings support the hypothesis that the extent of visual field per se cannot predict driving fitness, because some patients with HVFDs and advanced glaucoma can compensate for their deficit by effective visual scanning. Head movements appeared to be superior to eye and shoulder movements in predicting the outcome of the driving test under the present study scenario.

Eye-head coordination abnormalities in schizophrenia

BACKGROUND

Eye-movement abnormalities in schizophrenia are a well-established phenomenon that has been observed in many studies. In such studies, visual targets are usually presented in the center of the visual field, and the subject's head remains fixed. However, in every-day life, targets may also appear in the periphery. This study is among the first to investigate eye and head movements in schizophrenia by presenting targets in the periphery of the visual field.

METHODOLOGY/PRINCIPAL FINDINGS

Two different visual recognition tasks, color recognition and Landolt orientation tasks, were presented at the periphery (at a visual angle of 55° from the center of the field of view). Each subject viewed 96 trials, and all eye and head movements were simultaneously recorded using video-based oculography and magnetic motion tracking of the head. Data from 14 patients with schizophrenia and 14 controls were considered. The patients had similar saccadic latencies in both tasks, whereas controls had shorter saccadic latencies in the Landolt task. Patients performed more head movements, and had increased eye-head offsets during combined eye-head shifts than controls.

CONCLUSIONS/SIGNIFICANCE

Patients with schizophrenia may not be able to adapt to the two different tasks to the same extent as controls, as seen by the former's task-specific saccadic latency pattern. This can be interpreted as a specific oculomotoric attentional dysfunction and may support the hypothesis that schizophrenia patients have difficulties determining the relevance of stimuli. Patients may also show an uneconomic over-performance of head-movements, which is possibly caused by alterations in frontal executive function that impair the inhibition of head shifts. In addition, a model was created explaining 93% of the variance of the response times as a function of eye and head amplitude, which was only observed in the controls, indicating abnormal eye-head coordination in patients with schizophrenia.

Variable coordination of eye and head movements during the early development of attention: a longitudinal study of infants aged 12-36 months

This longitudinal study investigated the effects of attentional development on peripheral stimulus localization by analyzing the eye and head movements of toddlers as they matured from 12 to 36 months. On each trial of an experiment, a central fixation point and a 30° peripheral stimulus were presented, such that in the gap condition the fixation disappeared 300 ms before the peripheral stimulus, whereas in the no-overlap condition it disappeared simultaneously as the peripheral stimulus, and in the overlap condition the fixation remained present when the peripheral target occurred. Results showed that eye and head movement latencies were highly correlated in all conditions and ages. However, at 12 months, head movements were as fast as eye movements, whereas during the subsequent development, eye movements became increasingly faster than head movements. These findings are indicative of a transition between 12 and 36 months due either to a change in attentional control, or to changes in the size of the visual field in which only eye movements occur.

Stare in the crowd: frontal face guides overt attention independently of its gaze direction

Whether or not a stare in the midst of many faces can guide visual attention is a controversial issue. Two experiments are reported that investigate the hypothesis that visual attention is guided toward a frontal face in the search for a stare among faces with varied head angles. The participants were required to search for a face with a direct gaze in a context where the target could be at any of various head angles and the target's head angle was unpredictable in one trial. The search performance was better for a frontal-face target than for deviated-face targets. Furthermore, eye-movement analyses revealed that a frontal-face stimulus tended to be initially fixated prior to deviated-face stimuli, and many of the initially fixated frontal-face stimuli had an averted gaze. The findings suggest that a frontal face guides overt attention independently of its gaze direction in the search for a stare in a crowd. The validity of prioritising a frontal face in order to find a direct gaze among faces and the characteristics of a human-face detection system are discussed.

Learning the optimal control of coordinated eye and head movements

Various optimality principles have been proposed to explain the characteristics of coordinated eye and head movements during visual orienting behavior. At the same time, researchers have suggested several neural models to underly the generation of saccades, but these do not include online learning as a mechanism of optimization. Here, we suggest an open-loop neural controller with a local adaptation mechanism that minimizes a proposed cost function. Simulations show that the characteristics of coordinated eye and head movements generated by this model match the experimental data in many aspects, including the relationship between amplitude, duration and peak velocity in head-restrained and the relative contribution of eye and head to the total gaze shift in head-free conditions. Our model is a first step towards bringing together an optimality principle and an incremental local learning mechanism into a unified control scheme for coordinated eye and head movements.

Human beings and many other species redirect their gaze towards targets of interest through rapid gaze shifts known as saccades. These are made approximately three to four times every second, and larger saccades result from fast and concurrent movement of the animal's eyes and head. Experimental studies have revealed that during saccades, the motor system follows certain principles such as respecting a specific relationship between the relative contribution of eye and head motor systems to total gaze shift. Various researchers have hypothesized that these principles are implications of some optimality criteria in the brain, but it remains unclear how the brain can learn such an optimal behavior. We propose a new model that uses a plausible learning mechanism to satisfy an optimality criterion. We show that after learning, the model is able to reproduce motor behavior with biologically plausible properties. In addition, it predicts the nature of the learning signals. Further experimental research is necessary to test the validity of our model.

Effect of presbyopic vision corrections on perceptions of driving difficulty

OBJECTIVES

As the population ages, more people will be wearing presbyopic vision corrections when driving. However, little is known about the impact of these vision corrections on driving performance. This study aimed to determine the subjective driving difficulties experienced when wearing a range of common presbyopic contact lens and spectacle corrections.

METHODS

A questionnaire was developed and piloted that included a series of items regarding difficulties experienced while driving under daytime and nighttime conditions (rated on five-point and seven-point Likert scales). Participants included 255 presbyopic patients recruited through local optometry practices. Participants were categorized into five age-matched groups; including those wearing no vision correction for driving (n = 50), bifocal spectacles (n = 54), progressive spectacles (n = 50), monovision contact lenses (n = 53), and multifocal contact lenses (n = 48).

RESULTS

Overall, ratings of satisfaction during daytime driving were relatively high for all correction types. However, multifocal contact lens wearers were significantly less satisfied with aspects of their vision during nighttime than daytime driving, particularly regarding disturbances from glare and haloes. Progressive spectacle lens wearers noticed more distortion of peripheral vision, whereas bifocal spectacle wearers reported more difficulties with tasks requiring changes of focus and those who wore no optical correction for driving reported problems with intermediate and near tasks. Overall, satisfaction was significantly higher for progressive spectacles than bifocal spectacles for driving.

CONCLUSIONS

Subjective visual experiences of different presbyopic vision corrections when driving vary depending on the vision tasks and lighting level. Eye-care practitioners should be aware of the driving-related difficulties experienced with each vision correction type and the need to select corrective types that match the driving needs of their patients.

Cortical processing of head- and eye-gaze cues guiding joint social attention

Previous fMRI experiments showed an involvement of the STS in the processing of eye-gaze direction in joint attention. Since head-gaze direction can also be used for the assessment of another person's attentional focus, we compared the mechanisms underlying the processing of head- and eye-gaze direction using a combined psychophysical and fMRI approach. Subjects actively followed the head- or eye-gaze direction of a person in a photograph towards one of seven possible targets by moving their eyes. We showed that the right posterior superior temporal sulcus (STS) as well as the right fusiform gyrus (FSG) were involved in both processing of head- as well as eye-gaze direction. Another finding was a bilateral deactivation of a distinct area in the middle STS (mSTS) as well as the left anterior STS (aSTS), that was stronger when subjects followed eye-gaze direction than when they followed head-gaze direction. We assume that this deactivation is based on an active suppression of information arising from the distracting other directional cue, i.e. head-gaze direction in the eye-gaze direction task and eye-gaze direction in the head-gaze direction task. These results further support the hypothesis that the human equivalent of the gaze sensitive area in monkeys lies in more anterior parts of the STS than previously thought.