Cognitive Vergence Recorded with a Webcam-Based Eye-Tracker during an Oddball Task in an Elderly Population.

(1) Background: Our previous research provides evidence that vergence eye movements may significantly influence cognitive processing and could serve as a reliable measure of cognitive issues. The rise of consumer-grade eye tracking technology, which uses sophisticated imaging techniques in the visible light spectrum to determine gaze position, is noteworthy. In our study, we explored the feasibility of using webcam-based eye tracking to monitor the vergence eye movements of patients with Mild Cognitive Impairment (MCI) during a visual oddball paradigm. (2) Methods: We simultaneously recorded eye positions using a remote infrared-based pupil eye tracker. (3) Results: Both tracking methods effectively captured vergence eye movements and demonstrated robust cognitive vergence responses, where participants exhibited larger vergence eye movement amplitudes in response to targets versus distractors. (4) Conclusions: In summary, the use of a consumer-grade webcam to record cognitive vergence shows potential. This method could lay the groundwork for future research aimed at creating an affordable screening tool for mental health care.

Optimal twist angle for a graphene-like bilayer.

The first optimal-or 'magic'-angle leading to the nullity of the Dirac/Fermi velocity for twisted bilayer graphene is re-evaluated in the Bistritzer-MacDonald set-up (Bistritzer and MacDonald 2011Proc. Natl Acad. Sci.10812233-7). From the details of that calculation we study the resulting alterations when the properties of the two layers are not exactly the same. A moiré combination of lattices without relative rotation but with different spacing lengths may also lead to a vanishing Dirac velocity. Hopping amplitudes can vary as well, and curvature is one of the possible causes for their change. In the case of small curvature values and situations dominated by hopping energy scales, the optimal angle becomes wider than in the 'flat' case.

Atypical Arousal Regulation in Children With Autism but Not With Attention-Deficit/Hyperactivity Disorder as Indicated by Pupillometric Measures of Locus Coeruleus Activity.

BACKGROUND: Atypical arousal regulation may explain slower mean reaction time (MRT) in autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder compared with typical development. The locus coeruleus-norepinephrine system (LC-NE) underlies arousal regulation and adapts its activity to the utility of a task. LC-NE tonic and phasic activity are indexed by baseline pupil size (BPS) and stimulus-evoked pupillary response (SEPR). METHODS: The study assessed pupillometry in ASD (n = 31, 3 female/28 male), attention-deficit/hyperactivity disorder (n = 28, 3 female/25 male), and typically developing control subjects (n = 31, 16 female/15 male) during a visuospatial reaction-time task that manipulates arousal by conditions with low and high task utility. We estimated linear mixed models of BPS, SEPR, and MRT in a per-trial analysis to investigate arousal regulation of task performance. RESULTS: Slower MRT occurred in the ASD group compared with the typically developing control group during low-utility conditions while controlling for dimensional ASD and attention-deficit/hyperactivity disorder symptoms. In low-utility conditions, BPS and SEPR were inversely related and both were associated with faster MRT. Increased ASD symptoms across groups were associated with higher BPS during low-utility conditions. Changes in BPS and SEPR between task-utility conditions were smaller in the ASD group. CONCLUSIONS: Slower visuospatial task performance in ASD is specific to low task utility. Arousal was associated with task performance and showed altered activity in ASD. Increased BPS during low-utility conditions suggested increased LC-NE tonic activity as an ASD symptom marker in children. Smaller changes in BPS and SEPR in ASD indicated attenuated LC-NE activity adaptation in response to high-utility conditions. Slower performance and atypical arousal regulation are probably associated with attenuated LC-NE activity adaptation.

Spiking model of fixational eye movements and figure-ground segmentation.

We present a model connecting eye movements and cortical state. Its structure includes simulated retinal images, motion detection, feature detectors and layers of spiking neurons. The designed scheme shows how the effect of micro-saccadic scale eye movements can lead to successful figure segregation in a figure-ground paradigm, by inducing changes in the neural dynamics through the time evolution of the inhibition range.

Vergence eye movements during figure-ground perception.

Figure-ground, that is the segmentation of visual information into objects and their surrounding backgrounds, provides structure for visual attention. Recent evidence shows a novel role of vergence eye movements in visual attention. In the present work, vergence responses during figure-ground segregation tasks are psychophysically investigated. We show that during a figure-ground detection task, subjects convergence their eyes. Vergence eye movements are larger in figure trials than in ground trials. In detected figures trials, vergence are stronger than in trials where the figure went unnoticed. Moreover in figure trials, vergence responses are stronger to low-contrast figures than to high-contrast figures. We argue that these discriminative vergence responses have a role in figure-ground.

Altered Vergence Eye Movements and Pupil Response of Patients with Alzheimer's Disease and Mild Cognitive Impairment During an Oddball Task.

BACKGROUND: Alzheimer's disease (AD) is characterized by progressive deterioration of cognitive functions and may be preceded by mild cognitive impairment (MCI). Evidence shows changes in pupil and vergence responses related to cognitive processing of visual information. OBJECTIVE: Here we test the hypothesis that MCI and AD are associated with specific patterns in vergence and pupil responses. METHODS: We employed a visual oddball task. In the distractor condition (80%of the trials), a blue stimulus was presented whereas in the target condition (20%of trials) it was red. Participants (23 Controls, 33 MCI patients, and 18 AD patients) were instructed to press a button when a target appeared. RESULTS: Participants briefly converged their eyes 200 ms after stimulus presentation. In controls, this transient peak response was followed by a delay response to targets but not to distractor stimuli. In the patient groups, delay responses to distractors were noticed. Consequently, the differential vergence response was strong in the control group, weak in the MCI group, and absent in the AD group. Pupils started to dilate 500-600 ms after the appearance of a target but slightly contracted after the presentation of a distractor. This differential pupil response was strongest in the AD group. CONCLUSION: Our findings support the idea of a role of vergence and pupil responses in attention and reveal altered responses in MCI and AD patients. Further studies should assess the value of vergence and pupil measurements as an objective support tool for early diagnosis of AD.

Dynamic decorrelation as a unifying principle for explaining a broad range of brightness phenomena.

The visual system is highly sensitive to spatial context for encoding luminance patterns. Context sensitivity inspired the proposal of many neural mechanisms for explaining the perception of luminance (brightness). Here we propose a novel computational model for estimating the brightness of many visual illusions. We hypothesize that many aspects of brightness can be explained by a dynamic filtering process that reduces the redundancy in edge representations on the one hand, while non-redundant activity is enhanced on the other. The dynamic filter is learned for each input image and implements context sensitivity. Dynamic filtering is applied to the responses of (model) complex cells in order to build a gain control map. The gain control map then acts on simple cell responses before they are used to create a brightness map via activity propagation. Our approach is successful in predicting many challenging visual illusions, including contrast effects, assimilation, and reverse contrast with the same set of model parameters.

Eye Vergence Responses During an Attention Task in Adults With ADHD and Clinical Controls.

Objective: ADHD patients show poor oculomotor control and recent studies show that attention-related eye vergence is weak in ADHD children. We aimed to assess vergence as a potential diagnostic biomarker for ADHD in adults. Method: We assessed the modulation in the angle of vergence while performing an attention task (N = 144), comparing the results for adults previously diagnosed with ADHD (N = 108) with age-matched clinical controls (N = 36). Results: Significant differences in eye vergence response modulation between clinical controls and ADHD patients were documented. Diagnostic test accuracy was 79%. Conclusion: In combination with an attention task, eye vergence responses could be used as an objective marker to support the clinical diagnosis of adult ADHD.

Eye vergence responses in children with and without reading difficulties during a word detection task.

Vergence eye movements are movements of both eyes in opposite directions. Vergence is known to have a role in binocular vision. However recent studies link vergence eye movements also to attention and attention disorders. As attention may be involved in dyslexia, it is sensible to guess that the presence of reading difficulties can be associated with specific patterns in vergence responses. Data from school children performing a word-reading task have been analysed. In the task, children had to distinguish words from non-words (scrambled words or row of X's), while their eye positions were recorded. Our findings show that after stimulus presentation eyes briefly converge. These vergence responses depend on the stimulus type and age of the child, and are different for children with reading difficulties. Our findings support the idea of a role of attention in word reading and offer an explanation of altered attention in dyslexia.

Pupil dilation during visuospatial orienting differentiates between autism spectrum disorder and attention-deficit/hyperactivity disorder.

BACKGROUND: Previous research demonstrated atypical attention in children with attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Regarding visual orienting, findings suggest a differential impairment: Atypical orienting to relatively unexpected targets in ASD, and atypical processing of alerting cues in ADHD. The locus coeruleus-norepinephrine (LC-NE) system plays an important role in exploiting alerting cues to increase attention and task performance. The present study's aim was to examine differential subcortical processes underlying visual orienting in ASD and ADHD with pupil dilation (PD) as index of LC activity. METHODS: Pupil dilation (PD) progression metrics during visual orienting were calculated for task-evoked PD locked to cue, stimulus onset, and behavioral response. Group differences in PD and reaction time (RT) were compared between children with ASD without ADHD (ASD-) (N = 18), ADHD without ASD (ADHD-) (N = 28), both disorders (ASD + ADHD) (N = 14), and typically developing children (TD) (N = 31) using linear mixed models (LMM). To further explore the modulatory role of the LC-NE system group differences in the effect of task-evoked PD metrics on RT were examined exploratively. RESULTS: ASD (+ADHD) showed slower orienting responses to relatively unexpected spatial target stimuli as compared to TD, which was accompanied by higher PD amplitudes relative to ADHD- and TD. In ADHD-, shorter cue-evoked PD latencies relative to ASD-, ASD + ADHD, and TD were found. Group differences in the effect of cue- and stimulus-evoked PD amplitudes on RT were found in ASD- relative to TD. CONCLUSIONS: Study findings provide new evidence for a specific role of the LC-NE system in impaired reflexive orienting responses in ASD, and atypical visual processing of alerting cues in ADHD.

Novel Interactive Eye-Tracking Game for Training Attention in Children With Attention-Deficit/Hyperactivity Disorder.

OBJECTIVE: To assess whether the eye-tracking approach of the RECOGNeyes game has potential therapeutic benefits for children with neurodevelopmental disorders, in particular attention-deficit/hyperactivity disorder (ADHD). RECOGNeyes is a computer game that is played using the eyes as the game controller. The rationale behind the game is that individuals with ADHD have an underdeveloped attention control system. This attention control system is underdeveloped not because they lack this capacity but because this ability has not been sufficiently developed. The game was designed as an intervention for training visual attention in ADHD. METHODS: The sample included 28 children aged 8-15 years (18 aged < 12 y and 10 aged ≥ 12 y) previously diagnosed with ADHD (DSM-5 criteria). The participants were randomly divided into 2 groups. The experimental group played RECOGNeyes with eye-tracker for 3 weeks (3 times/week) at home, while the control group played the game using the mouse. Different attentional parameters were assessed before and after training. The study was conducted from January 2018-June 2018. RESULTS: Participants from the eye-tracker group showed an improvement posttest compared to pretest in impulsivity (P = .0067), reaction time (P < .0001), and fixation gaze control (P < .0001). No changes were found in mouse control between pretest and posttest assessments. CONCLUSION: RECOGNeyes is a child-friendly, interactive game combined with eye-tracking technology that seems to provide an improvement in the visual attention system, which is especially indicated for ADHD patients. This game might be used as an alternative to pharmacologic therapy and may provide new insights into the treatment of ADHD.​.

Eye vergence responses to novel and familiar stimuli in young children.

Eye vergence is the slow movement of both eyes in opposite directions enabling binocular vision. Recently, it was suggested that vergence could be involved in orienting visual attention and memory having a role in cognitive processing of sensory information. In the present study, we assessed whether such vergence responses are observed in early childhood. We measured eye vergence responses in 43 children (12-37 months of age) while looking at novel and repeated object images. Based on previous research, we hypothesized that visual attention and Visual Short-Term Memory (VSMT) would be evidenced by differential vergence responses for both experimental conditions, i.e. repeated (familiar) vs. novel items. The results show that attention related vergence is present in early childhood and that responses to repeated images differ from the ones to novel items. Our current findings suggest that vergence mechanisms could be linking visual attention with short-term memory recognition.

Luminance gradients and non-gradients as a cue for distinguishing reflectance and illumination in achromatic images: A computational approach.

The brain analyses the visual world through the luminance patterns that reach the retina. Formally, luminance (as measured by the retina) is the product of illumination and reflectance. Whereas illumination is highly variable, reflectance is a physical property that characterizes each object surface. Due to memory constraints, it seems plausible that the visual system suppresses illumination patterns before object recognition takes place. Since many combinations of reflectance and illumination can give rise to identical luminance values, finding the correct reflectance value of a surface is an ill-posed problem, and it is still an open question how it is solved by the brain. Here we propose a computational approach that first learns filter kernels ("receptive fields") for slow and fast variations in luminance, respectively, from achromatic real-world images. Distinguishing between luminance gradients (slow variations) and non-gradients (fast variations) could serve to constrain the mentioned ill-posed problem. The second stage of our approach successfully segregates luminance gradients and non-gradients from real-world images. Our approach furthermore predicts that visual illusions that contain luminance gradients (such as Adelson's checker-shadow display or grating induction) may occur as a consequence of this segregation process.

Clinical Validation of Eye Vergence as an Objective Marker for Diagnosis of ADHD in Children.

OBJECTIVE: ADHD youth show poor oculomotor control. Recent research shows that attention-related eye vergence is weak in ADHD children. METHOD: To validate vergence as a marker to classify ADHD, we assessed the modulation in the angle of vergence of children ( n = 43) previously diagnosed with ADHD while performing an attention task and compared the results with age-matched clinical controls ( n = 19) and healthy peers ( n = 30). RESULTS: We observed strong vergence responses in healthy participants and weak vergence in the clinical controls. ADHD children showed no significant vergence responses. Machine-learning models classified ADHD patients ( n = 21) from healthy controls ( n = 21) with an accuracy of 96.3% (false positive [FP]: 5.12%; false negative [FN]: 0%; area under the curve [AUC]: 0.99) and ADHD children ( n = 11) from clinical controls ( n = 14) with an accuracy of 85.7% (FP: 4.5%; FN: 19.2%, AUC: 0.90). CONCLUSION: In combination with an attention task, vergence responses can be used as an objective marker to detect ADHD in children.

Vergence responses to face stimuli in young children.

In line with a possible role of vergence in orienting visual attention, we sought to study this eye movement in young children to provide insights on face perception. For this purpose, we measured the modulation in the angle of eye vergence in a sample of 39 children aged 6-36 months and compared it when presenting static human face images versus their scrambled version. We observed enhanced vergence responses to faces compared with scrambled images. Our data suggest a role of eye vergence in face processing.

'Two vs one' rivalry by the Loxley-Robinson model.

We apply the competitive model of Loxley and Robinson (Phys Rev Lett 102:258701, 2009. doi: 10.1103/PhysRevLett.102.258701 ) to the study of a special case of visual rivalry. Three-peaked inputs with maxima at symmetrical locations are introduced, and the role of three-bump configurations is then considered. The model yields conditions for what can be interpreted as a bistable percept analogous to the one-dimensional version of a competition between the central and flanking parts of an image.

Bump competition and lattice solutions in two-dimensional neural fields.

Some forms of competition among activity bumps in a two-dimensional neural field are studied. First, threshold dynamics is included and rivalry evolutions are considered. The relations between parameters and dominance durations can match experimental observations about ageing. Next, the threshold dynamics is omitted from the model and we focus on the properties of the steady-state. From noisy inputs, hexagonal grids are formed by a symmetry-breaking process. Particular issues about solution existence and stability conditions are considered. We speculate that they affect the possibility of producing basis grids which may be combined to form feature maps.

Eye vergence responses during a visual memory task.

In a previous report it was shown that covertly attending visual stimuli produce small convergence of the eyes, and that visual stimuli can give rise to different modulations of the angle of eye vergence, depending on their power to capture attention. Working memory is highly dependent on attention. Therefore, in this study we assessed vergence responses in a memory task. Participants scanned a set of 8 or 12 images for 10 s, and thereafter were presented with a series of single images. One half were repeat images - that is, they belonged to the initial set - and the other half were novel images. Participants were asked to indicate whether or not the images were included in the initial image set. We observed that eyes converge during scanning the set of images and during the presentation of the single images. The convergence was stronger for remembered images compared with the vergence for nonremembered images. Modulation in pupil size did not correspond to behavioural responses. The correspondence between vergence and coding/retrieval processes of memory strengthen the idea of a role for vergence in attention processing of visual information.

Attentional Selection Accompanied by Eye Vergence as Revealed by Event-Related Brain Potentials.

Neural mechanisms of attention allow selective sensory information processing. Top-down deployment of visual-spatial attention is conveyed by cortical feedback connections from frontal regions to lower sensory areas modulating late stimulus responses. A recent study reported the occurrence of small eye vergence during orienting top-down attention. Here we assessed a possible link between vergence and attention by comparing visual event related potentials (vERPs) to a cue stimulus that induced attention to shift towards the target location to the vERPs to a no-cue stimulus that did not trigger orienting attention. The results replicate the findings of eye vergence responses during orienting attention and show that the strength and time of eye vergence coincide with the onset and strength of the vERPs when subjects oriented attention. Our findings therefore support the idea that eye vergence relates to and possibly has a role in attentional selection.

Global oscillation regime change by gated inhibition.

The role of sensory inputs in the modelling of synchrony regimes is exhibited by means of networks of spiking cells where the relative strength of the inhibitory interaction is controlled by the activation of a linear unit working as a gating variable. Adaptation to stimulus size is determined by the value of a changing length scale, modelled by the time-varying radius of a circular receptive field. In this set-up, 'consolidation' time intervals relevant to attentional effects are shown to depend on the dynamics governing the evolution of the introduced length scale.