Integration of allocentric and egocentric visual information in a convolutional / multilayer perceptron network model of goal-directed gaze shifts

Allocentric (landmark-centered) and egocentric (eye-centered) visual codes are fundamental for spatial cognition, navigation, and goal-directed movement. Neuroimaging and neurophysiology suggest these codes are segregated initially, but then reintegrated in frontal cortex for movement control. We created and validated a theoretical framework for this process using physiologically constrained inputs and outputs. To implement a general framework, we integrated a Convolutional Neural Network (CNN) of the visual system with a Multilayer Perceptron (MLP) model of the sensorimotor transformation. The network was trained on a task where a landmark shifted relative to the saccade target. These visual parameters were input to the CNN, the CNN output and initial gaze position to the MLP, and a decoder transformed MLP output into saccade vectors. Decoded saccade output replicated idealized training sets with various allocentric weightings, and actual monkey data where the landmark shift had a partial influence (R2 = 0.8). Furthermore, MLP output units accurately simulated prefrontal response field shifts recorded from monkeys during the same paradigm. In summary, our model replicated both the general properties of the visuomotor transformations for gaze and specific experimental results obtained during allocentric-egocentric integration, suggesting it can provide a general framework for understanding these and other complex visuomotor behaviors.

Enhanced Eye Velocity With Backup Saccades in vHIT Tests of a Menière Disease Patient: A Case Report

Reduced eye velocity and overt or covert compensatory saccades during horizontal head impulse testing are the signs of reduced vestibular function. However, here we report the unusual case of a patient who had enhanced eye velocity during horizontal head impulses followed by a corrective saccade. We term this saccade a “backup saccade” because it acts to compensate for the gaze position error caused by the enhanced velocity (and enhanced VOR gain) and acts to return gaze directly to the fixation target as shown by eye position records. We distinguish backup saccades from overt or covert compensatory saccades or the anticompensatory quick eye movement (ACQEM) of Heuberger et al. (1) ACQEMs are anticompensatory in that they are in the same direction as head velocity and so, act to take gaze off the target and thus require later compensatory (overt) saccades to return gaze to the target. Neither of these responses were found in this patient. The patient here was diagnosed with unilateral definite Meniere's disease (MD) on the right and had enhanced VOR (gain of 1.17) for rightward head impulses followed by backup saccades. For leftwards head impulses eye velocity and VOR gain were in the normal range (VOR gain of 0.89). As further confirmation, testing with 1.84 Hz horizontal sinusoidal head movements in the visual-vestibular (VVOR) paradigm also showed these backup saccades for rightwards head turns but normal slow phase eye velocity responses without backup saccades for leftwards had turns. This evidence shows that backup saccades can be observed in some MD patients who show enhanced eye velocity responses during vHIT and that these backup saccades act to correct for gaze position error caused by the enhanced eye velocity during the head impulse and so have a compensatory effect on gaze stabilization.

Similar cognitive processing synchronizes brains, hearts, and eyes

Neural, physiological and behavioral signals synchronize between human subjects in a variety of settings. Multiple hypotheses have been proposed to explain this interpersonal synchrony, but there is no clarity under which conditions it arises, for which signals, or whether there is a common underlying mechanism. We hypothesized that similar cognitive processing of a shared stimulus is the source of interpersonal synchrony, measured here as inter-subject correlation. To test this we presented informative videos to participants in an attentive and distracted condition and subsequently measured information recall. Inter-subject correlation was observed for electro-encephalography, gaze position, pupil size and heart rate, but not respiration and head movements. The strength of correlation was co-modulated in the different signals, changed with attentional state, and predicted subsequent recall of information presented in the videos. There was robust within-subject coupling between brain, heart and eyes, but not respiration or head movements. The results suggest that inter-subject correlation is the result of similar cognitive processing and thus emerges only for those signals that exhibit a robust brain-body connection. While physiological and behavioral fluctuations may be driven by multiple features of the stimulus, correlation with other individuals is co-modulated by the level of attentional engagement with the stimulus.SignificanceThe synchronization of human neural, physiological and behavioral signals happens in a variety of settings. In this work we show that physiological synchrony requires only two things, namely, effective cognitive processing of a common stimulus, and a robust coupling between brain activity and the physiological signal in question. We confirm this theory for heart rate, pupil size, gaze position and saccade rate, as positive examples, and respiration and head movements as negative examples. We show that the strength of this correlation is co-modulated, i.e. correlation is modulated in unison for all signals in which correlation is detected. We propose that this common modulation is the result of attentional engagement with the stimulus.

Relationship between eye movements and freezing of gait during turning in individuals with Parkinson disease

Background Individuals with Parkinson disease can experience freezing of gait: a sudden, brief episode of an inability to move their feet despite the intention to walk . Since turning is the most sensitive condition to provoke freezing-of-gait episodes, and the eyes typically lead turning, we hypothesize that disturbances in saccadic eye movements are related to freezing-of-gait episodes. Objectives This study explores the relationship between freezing-of-gait episodes and saccadic eye movements for gaze shift and gaze stabilization during turning. Methods We analyzed 277 freezing-of-gait episodes provoked among 17 individuals with Parkinson disease during two conditions: self-selected speed and rapid speed 180-degree turns in alternating directions. Eye movements acquired from electrooculography signals were characterized by the average position of gaze, the amplitude of gaze shifts, and the speed of gaze stabilization. We analyzed these variables before and during freezing-of-gait episodes occurring at the different phase angles of a turn. Results Significant off-track changes of the gaze position were observed almost one 180-degree-turn time before freezing-of-gait episodes. In addition, the speed of gaze stabilization significantly decreased during freezing-of-gait episodes. Conclusions We argue that off-track changes of the gaze position could be a predictor of freezing-of-gait episodes due to continued failure in movement-error correction or an insufficient preparation for eye-to-foot coordination during turning. The decline in the speed of gaze stabilization is large during freezing-of-gait episodes given the slowness or stop of body turning. We argue that this could be evidence for a healthy compensatory system in individuals with freezing-of-gait.

Using the Blind Spot to Investigate Trans-Saccadic Perception

We introduce a blind spot method to create image changes contingent on eye movements. One challenge of eye movement research is triggering display changes contingent on gaze. The eye-tracking system must capture the image of the eye, discover and track the pupil and corneal reflections to estimate the gaze position, and then transfer this data to the computer that updates the display. All of these steps introduce delays that are often difficult to predict. To avoid these issues, we describe a simple blind spot method to generate gaze contingent display manipulations without any eye-tracking system and/or display controls.

Study on the Effect of Gaze Position and Image Brightness on Peripheral Dimming Technique

Here, we study a low-power technique for displays based on gaze tracking, called peripheral dimming. In this work, the threshold levels of the lightness reduction ratio (LRR), where people notice differences in brightness, depending on gaze positions and image brightness, are investigated. A psychophysical experiment with five gaze positions and three image brightness conditions is performed, and the estimated threshold levels are obtained. To investigate the significance of the differences between the threshold levels, the overlap method and the Bayesian estimation (BEST) analysis are performed. The analysis results show that the difference of the threshold levels depending on the conditions is insignificant. Thus, the proposed technique can operate with a constant LRR level, regardless of the gaze position or image brightness, while maintaining the perceptual image quality. In addition, the proposed technique reduces the power consumption of virtual reality (VR) displays by 12–14% on average. We believe that the peripheral dimming technique would contribute to reducing the power of the self-luminous displays used for VR headsets with an integrated eye tracker.

Spatial asymmetries (“pseudoneglect”) in free visual exploration—modulation of age and relationship to line bisection

When humans visually explore an image, they typically tend to start exploring its left side. This phenomenon, so-called pseudoneglect, is well known, but its time-course has only sparsely been studied. Furthermore, it is unclear whether age influences pseudoneglect, and the relationship between visuo-spatial attentional asymmetries in a free visual exploration task and a classical line bisection task has not been established. To address these questions, 60 healthy participants, aged between 22 and 86, were assessed by means of a free visual exploration task with a series of naturalistic, colour photographs of everyday scenes, while their gaze was recorded by means of a contact-free eye-tracking system. Furthermore, a classical line bisection task was administered, and information concerning handedness and subjective alertness during the experiment was obtained. The results revealed a time-sensitive window during visual exploration, between 260 and 960 ms, in which age was a significant predictor of the leftward bias in gaze position, i.e., of pseudoneglect. Moreover, pseudoneglect as assessed by the line bisection task correlated with the average gaze position throughout a time-window of 300–1490 ms during the visual exploration task. These results suggest that age influences visual exploration and pseudoneglect in a time-sensitive fashion, and that the degree of pseudoneglect in the line bisection task correlates with the average gaze position during visual exploration in a time-sensitive manner.

Exophoria: clinical features, diagnosis, treatment. The modern view on the problem. Literature review

Purpose. Create a summary classification of exophoria. To propose an optimal algorithm for optometric and surgical methods of treatment. A modern view of the problem. It is optimal to subdivide exophoria according to the state of the vergent-duction balance into divergence excess, basic exophoria, convergence insufficiency, divergence pseudo-excess, lateral gaze incomitance. By the degree of compensation for compensated, subcompensated, uncompensated, decompensated. In combination with alphabetic pattern for exophoria without pattern, exophoria in combination with horizontal type A pattern, exophoria in combination with vertical type A pattern, exophoria in combination with horizontal type V pattern, exophoria in combination with vertical type V pattern. Features of optimal optical and prismatic correction depend on the state of the vergent-duction balance. In cases of exophoria without pattern surgical treatment is carried out during the transition from a state of subcompensation to non-compensation. In case of exophoria with horizontal-type alphabetical pattern, combined horizontal-transpositional surgery is optimal: elimination of exophoria, the protocol is based on the amount of deviation in the direct gaze position; elimination of the pattern, the protocol is based on vertical transposition of muscles of horizontal action. In cases of exophoria with vertical-type pattern, it is necessary to perform staged vertical-horizontal surgery: stage 1 – elimination of vertical heterotropy in adduction; stage 2 – elimination of exophoria (the protocol is based on the amount of deviation in the direct gaze position). Conclusions. The treatment protocol should be based on a reliably diagnosed diagnosis and consists at the pre-surgical stage in the optimal optical and prismatic correction, the appointment of orthopto-diplopto-prismatic treatment. The effectiveness of treatment is assessed by the dynamics of the disease: the magnitude of exodeviation and the stage of compensation. The protocol of surgical treatment must be reasonable and timely. Key words: exophoria, divergence excess, convergence insufficiency, basic exotropia, lateral gaze incomitance, alphabet pattern.

Joint treatment of severe amblyopia combined with uncomfortable esotropia (case report)

Purpose - to evaluate the effectiveness of a joint method for the treatment of severe amblyopia, combined with uncomfortable esotropia, including chemodenervation of the extraocular muscle and subsequent pleoptic treatment using the «Ambliokor» medical complex. Material and methods. The patient is 3 years old. Diagnosis: unfriendly non-paralytic esohypertropia with a prevalence of OD; amblyopia, severe OD, moderate OS, mixed astigmatism OU. The treatment was carried out in 2 stages. At the first stage in order to eliminate the dysbinocular factor of amblyopia, chemodenervation of the internal rectus muscle of the right eye with the preparation of botulinum toxin type A «Botox» was performed by the intraoperative technique. After 1 month, at the second stage, a complex pleoptic treatment was carried out. Results. After chemodenervation, 1 month later, orthotropy in the primary gaze position without glasses and with glasses was achieved. The vertical deviation significantly decreased to 5 degrees in the position of adduction of the eyeballs. The right lead was restored fully. The forced turn of the head was eliminated. After the third course of complex pleoptic treatment, visual acuity with correction was 0.7 on the right and 0.8 on the left. Restoration of central visual fixation in the right eye was noted. The simultaneous nature of vision was revealed. The deviation angle of the eyes in the primary gaze position without glasses and with glasses to the nose did not exceed +7 degrees according to Hirshberg. Hypertropia persisted in adduction up to 10 degrees according to Hirschberg (hyperfunction of the inferior oblique muscle) in both eyes. «V»-syndrome persisted. The patient is planned to surgically weaken the hyperfunction of the inferior oblique muscle of both eyes, followed by the continuation of a complex of pleopto-orthoptic treatment. Conclusion. The existing extensive base of various methods of influencing the functions of the amblyopic eye allows for successful treatment of even severe amblyopia. Key words: amblyopia, unfriendly esotropia, chemodenervation, pleoptic treatment.