Sensory Eye Dominance: Relationship Between Eye and Brain

Effects of binocularity and eye dominance on visually-driven ocular tracking

Introduction

We used 18 oculomotor performance metrics (oculometrics) to capture largely independent features of human ocular tracking. Our primary goal was to examine tracking eye movements in a healthy population under monocular and binocular viewing, as well as to examine the potential effects of line-of-sight eye dominance and spatial/directional tuning.

Methods

We compared the ocular responses of 17 healthy well-rested participants using a radial step-ramp paradigm under three viewing conditions: both-eyes viewing, left-eye viewing, and right-eye viewing.

Results

Our findings revealed that binocular viewing enhanced performance over that during monocular viewing for 11 oculometrics, with eye dominance associated with the selective enhancement of 3 oculometrics of visual motion processing. A comparison of binocular and dominant-eye viewing allowed us to segregate the direct enhancements of binocularity per se from those due simply to the inclusion of the dominant eye in binocular viewing and showed that viewing with two eyes is only directly responsible for the enhancement of 9 oculometrics. Our examination of spatial/directional tuning revealed largely isotropic enhancement due to binocularity, as well as several anisotropies in retinal functional processing: (1) a Nasal-Temporal asymmetry for pursuit latency and direction noise, and a Superior-Inferior asymmetry for latency, and (2) anisotropic enhancement in initial acceleration and direction noise (primarily for nasal retina) and speed noise (primarily for superior retina) when viewing through the dominant eye. We also documented Horizontal-Vertical anisotropies in initial acceleration, steady-state gain, proportion smooth, and speed responsiveness for both monocular and binocular viewing.

Conclusion

Our findings demonstrate that there is isotropic enhancement from binocular viewing per se across a wide range of visuomotor features and that important normative characteristics of visual motion processing are shaped by retinal processing non-uniformly across visual space, modulated by eye dominance and perhaps related to previously found normative structural anisotropies in retinal thickness. This constellation of findings characterizes the subtle natural non-linear variations in visuomotor performance to provide insight into the relative roles of the retina and other brain areas in shaping visuomotor performance and to enable the detection of neurological and ophthalmological impairment through comparison with properly matched baselines in support of future research and clinical applications.

Temporal Frequency Modulation of Binocular Balance in Normal and Amblyopic Vision

Purpose

To investigate how temporal frequency modulates binocular balance in normally sighted and amblyopic adults.

Methods

Twenty-three controls and 13 amblyopes participated in this study. The effects of temporal frequency differences and monocularly directed attention on binocular balance were measured using an onset binocular rivalry task with sinusoidally flickering gratings at varying temporal frequencies and static gratings with monocular attentional cues. For the flickering gratings, different combinations of temporal frequencies (2, 4, or 10 Hz in one eye vs. 2, 3, 4, 6, 10, 15, or 20 Hz in the other) were presented. Their effects were then compared, and their relationship was analyzed.

Results

There was no relationship between the shifts in balance from temporal frequency and monocularly directed attention in both controls and amblyopes. Intermediate temporal frequencies (8.9 ± 1.4 Hz) in one eye maximized its perceptual dominance, with a larger shift due to temporal frequency in amblyopes than in controls. While normally sighted observers experienced similar degrees of shift in balance from temporal frequency and attentional (active and passive) modulations, amblyopic observers experienced a larger shift from temporal frequency than from monocularly focused passive (but not active) attention.

Conclusions

Intermediate temporal frequencies in one eye, rather than a specific temporal frequency difference between both eyes, maximized its perceptual dominance in both normally sighted and amblyopic observers. This balance shift from temporal frequency modulation was larger in amblyopes than in controls. Finally, the effect of temporal frequency on balance was larger than that of monocularly directed passive attention in amblyopes.

Contextual Binocular Imbalance Impairs Local Stereopsis

Purpose

Binocular imbalance is known to inhibit stereopsis. This study investigates whether an imbalanced context around stereo stimuli also affects local stereopsis and explores the underlying mechanisms.

Methods

Three experiments were conducted with normally sighted participants. Experiment 1 measured local stereo detection thresholds under three context conditions: binocular balance (0.5 vs. 0.5 contrast), left-eye dominance (0.8 vs. 0.2 contrast), and right-eye dominance (0.2 vs. 0.8 contrast). Experiment 2 assessed the modulation of the imbalance effect by context-target collinearity. Experiment 3 examined the imbalance effect with binocular fusion and rivalry context stimuli.

Results

In experiment 1, the average stereo threshold was 62.4 arcsec in the binocular balance condition, elevated to 111.4 arcsec in the left-eye dominance (P = 0.003), and 114.7 arcsec in the right-eye dominance (P < 0.001), with no significant difference between the two imbalance conditions (P = 0.650). Experiment 2 showed that context-target collinearity modulated the imbalance effect, resulting in a smaller threshold elevation in the non-collinear condition (P = 0.011). Experiment 3 revealed significant main effects of imbalance (P = 0.031) and rivalry (P = 0.004), with no significant interaction (P = 0.966).

Conclusions

Contextual binocular imbalance inhibits local stereopsis, an effect modulated by collinearity and similarly observed in both binocular integrative and suppressive contexts. These findings suggest that lateral connectivity in the primary visual cortex (V1) plays a fundamental role in stereopsis generation, offering novel approaches for clinical interventions aimed at restoring binocular balance and stereopsis.

Visual simulation of intraocular lenses: technologies and applications [Invited]

Cataract surgery requires selecting an intraocular lens (IOL), whose design affects visual outcomes. Traditional IOL evaluation relies on optical models and bench testing, but these methods fall short in simulating perceptual factors crucial to patient experience. Visual simulators, based on different principles including adaptive optics, temporal multiplexing or physical projection of the IOLs, now allow patients and clinicians to preview and compare different IOL designs preoperatively. By simulating real-world interactions of the eye's optics and the visual system with IOLs, these simulators enhance the patient decision-making process, enable personalized cataract surgery, and can aid in regulatory assessments of IOLs by incorporating pre-operative patient-reported visual outcomes. Visual simulators incorporate deformable mirrors, spatial light modulators and optotunable lenses as dynamic elements to simulate monofocal, multifocal and extended depth-of-focus IOLs, including newer designs aimed at improving contrast sensitivity, expanding depth of focus, and minimizing visual disturbances. With ongoing advancements, these simulators hold potential for transforming IOL design, regulatory processes, and patient care by providing realistic and patient-centered visual assessments, ultimately leading to more successful, individualized surgical outcomes.

Quantifying sighting dominance using on-display projections of monocular and binocular views

Sighting dominance is an important behavioral property which has been difficult to measure quantitatively with high precision. We developed a measurement method that is grounded in a two-camera model that satisfies these aims. Using a simple alignment task, this method quantifies sighting ocular dominance during binocular viewing, identifying each eye's relative contribution to binocular vision. The method involves placing a physical target between the viewer and a display. The viewer indicates the perceived target's projection on the display with both eyes open and with only one eye open. The relative location of the binocular projection in relation to the two monocular projections is the index of dominance. The method produces a continuous variable with robust test-retest reliability (ICC = 0.96). The unit of measurement for the computed quantity is physiologically grounded: it is proportional to the distance between the monocular projections, which we show is predictable from interpupillary distance and phoria. Comparisons with the classic 'hole in card' sighting dominance test show good agreement, but also hint at potential bias for determining right-eye dominance in the latter. Interestingly, we find that some individuals systematically demonstrate nearly balanced vision, a phenomenon previously construed as mixed dominance or noisy responses. We also present ways to quantify and mitigate sources of random noise in this measurement. Overall, this new method allows for precise estimation of sighting dominance during binocular viewing. We expect it will allow a more effective understanding of the neural basis of dominance and improved effectiveness when using sighting dominance as a covariate in more complex analyses.

Transient eye closure and ocular preference in patients with intermittent exotropia

PURPOSE

To assess the relationship of sensory and motor ocular dominance to transient eye closure (TEC) under bright light conditions in patients with intermittent exotropia.

METHODS

Forty patients (age range, 7-40 years) with intermittent exotropia were included in this prospective study. Motor and sensory ocular dominance were evaluated using the hole-in-the-card and Worth 4-Dot tests. Presence of any outward eye deviation or TEC was assessed and recorded in all participants under bright light conditions. Based on the fusion control grade of exodeviation, patients were assigned to good, fair, and poor control groups, and the results were compared.

RESULTS

A total of 23 patients (58%) showed TEC under bright light: 18 (45%) in the good control group, 14 (35%) in the fair control group, and 8 (20%) in the poor control group. Eighteen patients (56%) with good and fair control showed TEC in the dominant eye. Five (63%) with poor control closed their nondominant eyes, and in all of them, outward eye deviation was observed before TEC. The angle of deviation at far and near and the degree of near stereopsis were not related to presence of TEC (P = 0.70, P = 0.06, and P = 0.34, resp.).

CONCLUSIONS

In patients with intermittent exotropia who exhibit TEC under bright light, those with good control tend to close the dominant eye, whereas in the majority of patients with poor control, spontaneous deviation occurs and is then followed by TEC of the nondominant eye.

Factors Affecting Stimulus Duration Threshold for Depth Discrimination of Asynchronous Targets in the Intermediate Distance Range

Purpose

Binocular depth discrimination in the near distance range (< 2 m) improves with stimulus duration. However, whether the same response-pattern holds in the intermediate distance range (approximately 2-25 m) remains unknown because the spatial coding mechanisms are thought to be different.

Methods

We used the two-interval forced choice procedure to measure absolute depth discrimination of paired asynchronous targets (3, 6, or 16 arc min). The paired targets (0.2 degrees) were located over a distance and height range, respectively, of 4.5 to 7.0 m and 0.15 to 0.7 m. Experiment 1 estimated duration thresholds for binocular depth discrimination at varying target durations (40-1610 ms), in the presence of a 2 × 6 array of parallel texture-elements spanning 1.5 × 5.83 m on the floor. The texture-elements provided a visible background in the light-tight room (9 × 3 m). Experiment 2 used a similar setup to control for viewing conditions: binocular versus monocular and with versus without texture background. Experiment 3 compared binocular depth discrimination between brief (40, 80, and 125 ms) and continuous texture background presentation.

Results

Stimulus duration threshold for depth discrimination decreased with increasing disparity in experiment 1. Experiment 2 revealed depth discrimination performance with texture background was near chance level with monocular viewing. Performance with binocular viewing degraded without texture background. Experiment 3 showed continuous texture background presentation enhances binocular depth discrimination.

Conclusions

Absolute depth discrimination improves with target duration, binocular viewing, and texture background. Performance further improved with longer background duration underscoring the role of ground surface representation in spatial coding.

Age-related analysis of corneal biomechanical parameters in healthy Chinese individuals

To report the correlation between corneal biomechanical parameters and age in healthy Chinese individuals. This cross-sectional study was conducted on 864 eyes of 543 healthy participants. A comprehensive ophthalmic examination and corneal biomechanics examination using Corneal Visualization Scheimpflug Technology (Corvis ST) were conducted. Based on age, all participants were further divided into five age groups (n) as follows: group A, 11-20 years (105); group B, 21-30 years (112); group C, 31-40 years (113); group D, 41-50 years (100); and group E, > 50 years (113). Using Corvis ST, we examined 35 corneal biomechanical parameters and compared them across the different age groups. Spearman's correlation coefficients and stepwise multivariate linear regression models were used to investigate whether the corneal biomechanical parameters were related to demographic and ocular characteristics. A correlation analysis between the left and right eyes revealed that 13 parameters were significantly associated with eye differences. Among the 35 corneal biomechanical parameters, 28 exhibited significant differences across the age groups, with stiffness parameter at applanation 1(SPA1) showing an upward trend after the age of 30 and stress-strain index (SSI) demonstrates a statistically significant upward trend when comparing the five age groups in the study. Additionally, Spearman's correlation analysis and stepwise multivariate linear regression analysis revealed that 11 corneal biomechanical parameters were positively correlated with age and 10 were negatively correlated with age. Corvis biomechanical index (CBI) was significantly negatively correlated with intraocular pressure (IOP) and central corneal thickness (CCT), SSI was significantly positively correlated with age and IOP, and SPA1 were positively correlated with IOP and CCT. In conclusion, most corneal biomechanical parameters showed a significant correlation with age, with corneal stiffness progressively increasing alongside advancing age, IOP, or CCT.

The effect of ocular dominance on choroidal structures

This study aimed to compare the dominant and non-dominant eyes of healthy individuals in terms of CT and CVI values to assess the effect of ocular dominance on choroidal morphology. Three hundred eyes of 150 individuals were included in this study. All patients underwent routine ophthalmological examinations and hole-in-the-card tests to determine the dominant eye. EDI-OCT was used to obtain choroidal images. Choroidal thickness (CT) was measured at three points on the choroid including the subfoveal region (subfoveal choroidal thickness (SFCT)), 1500 μm nasal (NCT) and temporal (TCT) to the fovea. Choroidal vascularity index (CVI), total choroidal area (TCA), luminal area (LA), and stromal area (SA) were measured at fovea-centered choroidal area by image binarization via Image J software. While 93(%62) participants were right-eyed, 57(%38) participants were left-eyed. We could not detect any difference in SFCT, NCT, TCT, TCA, LA, SA, and CVI measurements between the dominant and the non-dominant eyes. (p > 0.05 for all). We could not detect any effect of ocular dominance on choroidal structures. These results also support the use of randomized ocular data regardless of which eye is dominant when investigating CVI and CT in scientific research.

Adaptation of Ocular Opponency Neurons Mediates Attention-Induced Ocular Dominance Plasticity

Previous research has shown that ocular dominance can be biased by prolonged attention to one eye. The ocular-opponency-neuron model of binocular rivalry has been proposed as a candidate account for this phenomenon. Yet direct neural evidence is still lacking. By manipulating the contrast of dichoptic testing gratings, here we measured the steady-state visually evoked potentials (SSVEPs) at the intermodulation frequencies to selectively track the activities of ocular-opponency-neurons before and after the "dichoptic-backward-movie" adaptation. One hour of adaptation caused a shift of perceptual and neural ocular dominance towards the unattended eye. More importantly, we found a decrease in the intermodulation SSVEP response after adaptation, which was significantly greater when high-contrast gratings were presented to the attended eye than when they were presented to the unattended eye. These results strongly support the view that the adaptation of ocular-opponency-neurons contributes to the ocular dominance plasticity induced by prolonged eye-based attention.

Short-Term Modulation of Online Monocular Visuomotor Function

Previous literature suggests that correcting ongoing movements is more effective when using the dominant limb and seeing with the dominant eye. Specifically, individuals are more effective at adjusting their movement to account for an imperceptibly perturbed or changed target location (i.e., online movement correction), when vision is available to the dominant eye. However, less is known if visual-motor functions based on monocular information can undergo short-term neuroplastic changes after a bout of practice, to improve online correction processes. Participants (n = 12) performed pointing movements monocularly and their ability to correct their movement towards an imperceptibly displaced target was assessed. On the first day, the eye associated with smaller correction amplitudes was exclusively trained during acquisition. While correction amplitude was assessed again with both eyes monocularly, only the eye with smaller correction amplitudes in the pre-test showed significant improvement in delayed retention. These results indicate that monocular visuomotor pathways can undergo short-term neuroplastic changes.

Binocular balance across spatial frequency in anisomyopia

Purpose

Anisomyopia is prevalent in myopia and studies have reported it exhibits impaired binocular function. We investigated the binocular balance across spatial frequency in adults with anisomyopia and compared it to in individuals with less differences in refractive error, and examined whether ocular characteristics can predict binocular balance in anisomyopia.

Methods

Fifteen anisomyopes, 15 isomyopes and 12 emmetropes were recruited. Binocular balance was quantitatively measured at 0.5, 1, 2 and 4 c/d. The first two groups of the observers were tested with and without optical correction with contact lenses. Emmetropes were tested without optical correction.

Results

Binocular balance across spatial frequency in optically corrected anisomyopes and isomyopes, as well as emmetropes were found to be similar. Their binocular balance nevertheless still got worse as a function of spatial frequency. However, before optical correction, anisomyopes but not isomyopes showed significant imbalance at higher spatial frequencies. There was a significant correlation between the dependence on spatial frequency of binocular imbalance in uncorrected anisomyopia and interocular difference in visual acuity, and between the dependence and interocular difference in spherical equivalent refraction.

Conclusion

Anisomyopes had intact binocular balance following correction across spatial frequency compared to those in isomyopes and emmetropes. Their balance was weakly correlated with their refractive status after optical correction. However, their binocular balance before correction and binocular improvement following optical correction were strongly correlated with differences in ocular characteristics between eyes.

Integration and suppression interact in binocular vision

Contingent on stereo compatibility, two images presented dichoptically can lead to either binocular integration, thus generating stable stereopsis, or interocular suppression that induces binocular rivalry with bistable perception that alternates between the two images. The relationship between binocular integration and interocular suppression concerns how our brain processes binocular inputs to form unified visual awareness but remains unclear. Here, a series of psychophysical experiments were conducted to address this question, revealing that these collaborative and competitive binocular interactions are interconnected and would mediate one another according to their strength. Specifically, Experiments 1a and 1b showed that the presence of binocular rivalry inhibited peripheral stereopsis, significantly elevating the stereo threshold, with higher elevation resulting from increasing rivalry contrast. Experiments 2a and 2b showed that existing stereopsis with increasing binocular disparity balanced the dynamics of peripheral binocular rivalry, rendering more equivalent eye dominance. Based on these interactions, we suggest that binocular integration and interocular suppression may mediate one another through an overlapping mechanism for regulating eye dominance, with strong stereo percepts tending to reduce eye dominance and strong rivalry tending to increase eye dominance.

Measuring the reliability of binocular rivalry

Binocular rivalry is a widely used tool in sensory and cognitive neuroscience to investigate different aspects of vision and cognition. The dynamics of binocular rivalry (e.g., duration of perceptual dominance phases and mixed percept proportions) differ across individuals; based on rivalry dynamics, it is also possible to calculate an index of ocular dominance (by comparing the perceptual dominance of the images in the two eyes). In this study, we investigated the reliability of binocular rivalry dynamics using different methods for dichoptic stimulation and different rivalry stimuli. For the three main indices we defined (ocular dominance, phase durations and mixed percept proportions), we found a high test-retest reliability across sessions. Moreover, the test-retest reliability of the ocular dominance index was predictable from its internal consistency, supporting its stability over time. Phase durations and mixed percept proportions, in contrast, had worse test-retest reliability than expected based on internal consistency, indicating that these parameters are susceptible to state-dependent changes. Our results support the use of the ocular dominance index and binocular rivalry in the measurement of sensory eye dominance and its plasticity, but advise caution when investigating the association between phase durations or mixed percepts and stable characteristics like psychological traits or disorders.

Does V1 response suppression initiate binocular rivalry?

During binocular rivalry (BR) only one eye's view is perceived. Neural underpinnings of BR are debated. Recent studies suggest that primary visual cortex (V1) initiates BR. One trigger might be response suppression across most V1 neurons at the onset of BR. Here, we utilize a variant of BR called binocular rivalry flash suppression (BRFS) to test this hypothesis. BRFS is identical to BR, except stimuli are shown with a ∼1s delay. If V1 response suppression was required to initiate BR, it should occur during BRFS as well. To test this, we compared V1 spiking in two macaques observing BRFS. We found that BRFS resulted in response facilitation rather than response suppression across V1 neurons. However, BRFS still reduces responses in a subset of V1 neurons due to the adaptive effects of asynchronous stimulus presentation. We argue that this selective response suppression could serve as an alternate initiator of BR.

Design guidelines for limiting and eliminating virtual reality-induced symptoms and effects at work: a comprehensive, factor-oriented review

Virtual reality (VR) can induce side effects known as virtual reality-induced symptoms and effects (VRISE). To address this concern, we identify a literature-based listing of these factors thought to influence VRISE with a focus on office work use. Using those, we recommend guidelines for VRISE amelioration intended for virtual environment creators and users. We identify five VRISE risks, focusing on short-term symptoms with their short-term effects. Three overall factor categories are considered: individual, hardware, and software. Over 90 factors may influence VRISE frequency and severity. We identify guidelines for each factor to help reduce VR side effects. To better reflect our confidence in those guidelines, we graded each with a level of evidence rating. Common factors occasionally influence different forms of VRISE. This can lead to confusion in the literature. General guidelines for using VR at work involve worker adaptation, such as limiting immersion times to between 20 and 30 min. These regimens involve taking regular breaks. Extra care is required for workers with special needs, neurodiversity, and gerontechnological concerns. In addition to following our guidelines, stakeholders should be aware that current head-mounted displays and virtual environments can continue to induce VRISE. While no single existing method fully alleviates VRISE, workers' health and safety must be monitored and safeguarded when VR is used at work.

Short-term homeostatic visual neuroplasticity in adolescents after two hours of monocular deprivation

In healthy adults with normal vision, temporary deprivation of one eye's visual experience produces transient yet robust homeostatic plasticity effects, where the deprived eye becomes more dominant. This shift in ocular dominance is short-lived and compensatory. Previous work shows that monocular deprivation decreases resting state gamma aminobutyric acid (GABA; inhibitory neurotransmitter) levels in visual cortex, and that those with the greatest reduction in GABA have stronger shifts due to monocular deprivation. Components of the GABAergic system in visual cortex vary with age (early childhood, early teen years, ageing); hence if GABA is critical to homeostatic plasticity within the visual system, adolescence may be a key developmental period where differences in plasticity manifest. Here we measured short-term visual deprivation effects on binocular rivalry in 24 adolescents (aged 10-15 years) and 23 young adults (aged 20-25 years). Despite differences in baseline features of binocular rivalry (adolescents showed more mixed percept p < 0.001 and a tendency for faster switching p = 0.06 compared to adults), deprived eye dominance increased (p = 0.01) similarly for adolescents and adults after two hours of patching. Other aspects of binocular rivalry - time to first switch (heralding the onset of rivalry) and mixed percept - were unaltered by patching. These findings suggest that binocular rivalry after patching can be used as a behavioral proxy for experience-dependent visual cortical plasticity in adolescents in the same way as adults, and that homeostatic plasticity to compensate for temporarily reduced visual input is established and effective by adolescence.

Complications of Small Aperture Intracorneal Inlays: A Literature Review

Presbyopia can be defined as the refractive state of the eye in which, due to a physiological decrease in the ability to accommodate, it is not possible to sustain vision without fatigue in a prolonged manner, along with difficulty focusing near vision. It is estimated that its prevalence in 2030 will be approximately 2.1 billion people. Corneal inlays are an alternative in the correction of presbyopia. They are implanted beneath a laser-assisted in situ keratomileusis (LASIK) flap or in a pocket in the center of the cornea of the non-dominant eye. The purpose of this review is to provide information about intraoperative and postoperative KAMRA inlay complications in the available scientific literature. A search was conducted on PubMed, Web of Science, and Scopus with the following search strategy: ("KAMRA inlay" OR "KAMRA" OR "corneal inlay pinhole" OR "pinhole effect intracorneal" OR "SAICI" OR "small aperture intracorneal inlay") AND ("complication" OR "explantation" OR "explanted" OR "retired"). The bibliography consulted shows that the insertion of a KAMRA inlay is an effective procedure that improves near vision with a slight decrease in distance vision. However, postoperative complications such as corneal fibrosis, epithelial iron deposits, and stromal haze are described.

Neural Correlates of Sensory Eye Dominance in Human Visual White Matter Tracts

A significant proportion of the human neurotypical population exhibits some degree of sensory eye dominance (SED), referring to the brain's preferential processing of one eye's input versus another. The neural substrates underlying this functional imbalance are not well known. Here, we investigated the relationship between visual white matter tract properties and SED in the human neurotypical population. Observers' performance on two commonly used dichoptic tasks were used to index SED, along with performance on a third task to address a functional implication of binocular imbalance: stereovision. We show that diffusivity metrics of the optic radiations (ORs) well predict behavioral SED metrics. We found no relationship between SED and stereosensitivity. Our data suggest that SED is not simply reflected by gray matter structural and functional alterations, as often suggested, but relates, at least in part to the microstructural properties of thalamocortical white matter.

The effect of spatial structure on binocular contrast perception

To obtain a single percept of the world, the visual system must combine inputs from the two eyes. Understanding the principles that govern this binocular combination process has important real-world clinical and technological applications. However, most research examining binocular combination has relied on relatively simple visual stimuli and it is unclear how well the findings apply to real-world scenarios. For example, it is well-known that, when the two eyes view sine wave gratings with differing contrast (dichoptic stimuli), the binocular percept often matches the higher contrast grating. Does this winner-take-all property of binocular contrast combination apply to more naturalistic imagery, which include broadband structure and spatially varying contrast? To better understand binocular combination during naturalistic viewing, we conducted psychophysical experiments characterizing binocular contrast perception for a range of visual stimuli. In two experiments, we measured the binocular contrast perception of dichoptic sine wave gratings and naturalistic stimuli, and asked how the contrast of the surrounding context affected percepts. Binocular contrast percepts were close to winner-take-all across many of the stimuli when the surrounding context was the average contrast of the two eyes. However, we found that changing the surrounding context modulated the binocular percept of some patterns and not others. We show evidence that this contextual effect may be due to the spatial orientation structure of the stimuli. These findings provide a step toward understanding binocular combination in the natural world and highlight the importance of considering the effect of the spatial interactions in complex stimuli.

A nasal visual field advantage in interocular competition

When our eyes are confronted with discrepant images (yielding incompatible retinal inputs) interocular competition (IOC) is instigated. During IOC, one image temporarily dominates perception, while the other is suppressed. Many factors affecting IOC have been extensively examined. One factor that received surprisingly little attention, however, is the stimulus’ visual hemifield (VHF) of origin. This is remarkable, as the VHF location of stimuli is known to affect visual performance in various contexts. Prompted by exploratory analyses, we examined five independent datasets of breaking continuous flash suppression experiments, to establish the VHF’s role in IOC. We found that targets presented in nasal VHF locations broke through suppression much faster than targets in temporal VHF locations. Furthermore, we found that the magnitude of this nasal advantage depended on how strongly the targets were suppressed: the nasal advantage was larger for the recessive eye than for the dominant eye, and was larger in observers with a greater dominance imbalance between the eyes. Our findings suggest that the nasal advantage reported here originates in processing stages where IOC is resolved. Finally, we propose that a nasal advantage in IOC serves an adaptive role in human vision, as it can aid perception of partially occluded objects.

GABAergic inhibition in the human visual cortex relates to eye dominance

Binocular vision is created by fusing the separate inputs arriving from the left and right eyes. 'Eye dominance' provides a measure of the perceptual dominance of one eye over the other. Theoretical models suggest that eye dominance is related to reciprocal inhibition between monocular units in the primary visual cortex, the first location where the binocular input is combined. As the specific inhibitory interactions in the binocular visual system critically depend on the presence of visual input, we sought to test the role of inhibition by measuring the inhibitory neurotransmitter GABA during monocular visual stimulation of the dominant and the non-dominant eye. GABA levels were measured in a single volume of interest in the early visual cortex, including V1 from both hemispheres, using a combined functional magnetic resonance imaging and magnetic resonance spectroscopy (combined fMRI-MRS) sequence on a 7-Tesla MRI scanner. Individuals with stronger eye dominance had a greater difference in GABAergic inhibition between the eyes. This relationship was present only when the visual system was actively processing sensory input and was not present at rest. We provide the first evidence that imbalances in GABA levels during ongoing sensory processing are related to eye dominance in the human visual cortex. Our finding supports the view that intracortical inhibition underlies normal eye dominance.

Some psychophysical tasks measure ocular dominance plasticity more reliably than others

In the recent decade, studies have shown that short-term monocular deprivation strengthens the deprived eye's contribution to binocular vision. However, the magnitude of the change in eye dominance after monocular deprivation (i.e., the patching effect) has been found to be different between different methods and within the same method. There are three possible explanations for the discrepancy. First, the mechanisms underlying the patching effect that are probed by different measurement tasks might exist at different neural sites. Second, the test–retest variability of the same test can produce inconsistent results. Third, the magnitude of the patching effect itself within the same observer can vary across separate days or experimental sessions. To explore these possibilities, we assessed the test–retest reliability of the three most commonly used tasks (binocular rivalry, binocular combination, and dichoptic masking) and the repeatability of the shift in eye dominance after short-term monocular deprivation for each of the task. Two variations for binocular phase combination were used, at one and many contrasts of the stimuli. Also, two variations for dichoptic masking were employed; the orientation of the mask grating was either horizontal or vertical. Thus, five different tasks were evaluated. We hoped to resolve some of the inconsistencies reported in the literature concerning this form of visual plasticity. In this study, we also aimed to recommend a measurement method that would allow us to better understand its physiological basis and the underpinning of visual disorders.

Investigating the neurochemistry of the human visual system using magnetic resonance spectroscopy

Biochemical processes underpin the structure and function of the visual cortex, yet our understanding of the fundamental neurochemistry of the visual brain is incomplete. Proton magnetic resonance spectroscopy (¹H-MRS) is a non-invasive brain imaging tool that allows chemical quantification of living tissue by detecting minute differences in the resonant frequency of molecules. Application of MRS in the human brain in vivo has advanced our understanding of how the visual brain consumes energy to support neural function, how its neural substrates change as a result of disease or dysfunction, and how neural populations signal during perception and plasticity. The aim of this review is to provide an entry point to researchers interested in investigating the neurochemistry of the visual system using in vivo measurements. We provide a basic overview of MRS principles, and then discuss recent findings in four topics of vision science: (i) visual perception, plasticity in the (ii) healthy and (iii) dysfunctional visual system, and (iv) during visual stimulation. Taken together, evidence suggests that the neurochemistry of the visual system provides important novel insights into how we perceive the world.

Ocular Dominance and Functional Asymmetry in Visual Attention Networks

Purpose

The dorsal attention network (DAN) and the ventral attention network (VAN) are known to support visual attention, but the influences of ocular dominance on the attention networks are unclear. We aimed to explore how visual cortical asymmetry of the attention networks correlate with neurophysiological oscillation and connectivity markers of attentional processes.

Methods

An oddball task with concentric circle stimuli of three different sizes (i.e., spot size of 5°, 20°, or 30° of visual angle) was used to vary task difficulty. Event-related oscillations and interareal communication were tested with an electroencephalogram-based visual evoked components as a function of ocular dominance in 30 healthy subjects.

Results

Accuracy rates were higher in the dominant eyes compared with the nondominant eyes. Compared with the nondominant eyes, the dominant eyes had higher theta, low-alpha, and low-beta powers and lower high-alpha powers within the nodes of VAN and DAN. Furthermore, visual information processed by the dominant and nondominant eye had different fates, that is, the dominant eyes mainly relied on theta and low-alpha connectivity within both the VAN and the DAN, whereas the nondominant eyes mainly relied on theta connectivity within the VAN and high-alpha connectivity within the DAN. The difference in accuracy rate between the two eyes was correlated with the low-alpha oscillations in the anterior DAN area and low-alpha connectivity of the left DAN.

Conclusions

The ocular dominance processing and interareal communication reveal a cortical asymmetry underlying attention, and this reflects a two-way modulatory mechanism within attention networks in the human brain.

The ups and downs of sensory eye balance: Monocular deprivation has a biphasic effect on interocular dominance

Classic studies of ocular dominance plasticity in early development showed that monocular deprivation suppresses the neural representation and visual function of the deprived eye. However, recent studies have shown that a short period of monocular deprivation (<3 h) in normal adult humans, shifts sensory eye dominance in favor of the deprived eye. How can these opposing effects be reconciled? Here we argue that there are two systems acting in opposition at different time scales. A fast acting, stabilizing, homeostatic system that rapidly decreases gain in the non-deprived eye or increases gain in the deprived eye, and a relatively sluggish system that shifts balance toward the non-deprived eye, in an effort to reduce input of little utility to active vision. If true, then continuous deprivation should produce a biphasic effect on interocular balance, first shifting balance away from the non-deprived eye, then towards it. Here we investigated the time course of the deprivation effect by monocularly depriving typical adults for 10 h and conducting tests of sensory eye balance at six intervening time points. Consistent with previous short-term deprivation work, we found shifts in sensory eye dominance away from the non-deprived eye up until approximately 5 h. We then observed a turning point, with balance shifting back towards the non-deprived eye, -, a biphasic effect. We argue that this turning point marks where the rapid homeostatic response saturates and is overtaken by the slower system responsible for suppressing monocular input of limited utility.