Gabor Patches Research Articles

A Model of the Early Visual System Based on Parallel Spike-Sequence Detection, Showing Orientation Selectivity.

Simple SummaryA computational model of primates’ early visual processing, showing orientation selectivity, is presented. The system importantly integrates two key elements: (1) a neuromorphic spike-decoding structure that considerably resembles the circuitry between layers IV and II/III of the primary visual cortex, both in topology and operation; (2) the plasticity of intrinsic excitability, to embed recent findings about the operation of the same area. The model is proposed as a tool for the analysis and reproduction of the orientation selectivity phenomenon, whose underlying neuronal-level computational mechanisms are today the subject of intense scrutiny. In response to rotated Gabor patches the model is able to exhibit realistic orientation tuning curves and to reproduce responses similar to those found in neurophysiological recordings from the primary visual cortex obtained under the same task, considering different stages of the network. This demonstrates its aptness to capture the mechanisms underlying the evoked response in the primary visual cortex. Our tool is available online, and can be expanded to other experiments using a dedicated software library developed by the authors, to elucidate the computational mechanisms underlying orientation selectivity.Since the first half of the twentieth century, numerous studies have been conducted on how the visual cortex encodes basic image features. One of the hallmarks of basic feature extraction is the phenomenon of orientation selectivity, of which the underlying neuronal-level computational mechanisms remain partially unclear despite being intensively investigated. In this work we present a reduced visual system model (RVSM) of the first level of scene analysis, involving the retina, the lateral geniculate nucleus and the primary visual cortex (V1), showing orientation selectivity. The detection core of the RVSM is the neuromorphic spike-decoding structure MNSD, which is able to learn and recognize parallel spike sequences and considerably resembles the neuronal microcircuits of V1 in both topology and operation. This structure is equipped with plasticity of intrinsic excitability to embed recent findings about V1 operation. The RVSM, which embeds 81 groups of MNSD arranged in 4 oriented columns, is tested using sets of rotated Gabor patches as input. Finally, synthetic visual evoked activity generated by the RVSM is compared with real neurophysiological signal from V1 area: (1) postsynaptic activity of human subjects obtained by magnetoencephalography and (2) spiking activity of macaques obtained by multi-tetrode arrays. The system is implemented using the NEST simulator. The results attest to a good level of resemblance between the model response and real neurophysiological recordings. As the RVSM is available online, and the model parameters can be customized by the user, we propose it as a tool to elucidate the computational mechanisms underlying orientation selectivity.

Luminance contrast detection is optimized for the large‐scale luminance texture of the surround

AbstractContrast sensitivity functions (CSFs) have been typically measured under persistent adaptation to a uniform background. However, this is an unusual situation, considering that visual scenes in our daily lives are typically filled by objects of various luminance levels in a wide dynamic range. We investigated the interactions between the luminance range of textured adapting background and test luminance (luminance of an immediate surround) to see how the contrast sensitivities adapt to background luminance distributions. The background was a random array of one‐dimensional lines, which had a maximum luminance range of approximately 1:520 000, and the test stimulus was a Gabor patch presented on an immediate uniform surround with various luminance levels. The carrier orientation of the Gabor patch was orthogonal to that of the background lines. In the results, the sensitivity was highest near the mean of background luminance, and the luminance range with the highest sensitivity became wider (i.e., the selectivity of sensitivity optimization weakened) as the background luminance range became larger. This sensitivity optimization was significant mainly in the lower spatial frequency. These results indicate that the overall contrast sensitivity is adjusted to the luminance range of the visual scene and the sensitivity optimization is more flexible in relatively lower spatial frequency.

Automated grating contrast-sensitivity: The easy test for hidden visual loss in recovered optic neuritis patient.

PURPOSE:Residual visual loss is an important predictor of optic neuritis relapse and progression. This study aimed to investigate the hidden residual visual loss in patients with optic neuritis using automated contrast-sensitivity (CS) function testing.MATERIALS AND METHODS:This cross-sectional study investigated 29 recovered optic neuritis patients (age: 27.69 ± 13.32 years, range: 13–51). Twenty age-matched controls with normal visual acuity (VA, in LogMAR) were recruited, for comparison with patients' VA and CS function after stable recovery from optic neuritis (6 months of follow-up). CS tests used a novel software that displays a single set of Gabor patches (2 cycles per degree at 10° ×10° of visual angle) with contrasts grating from 100% to 0.1%.RESULTS:There were 13 adolescent patients (63.6%: retrobulbar neuritis [RN]; 36.4%: papillitis), 14 adult patients (50%: RN; 42.9%: papillitis), and only 2 older patients (all with neuroretinitis). There was improvement of VA in the patient group at first diagnosis and follow-up (VA initial vs. final: 1.438 ± 1.134 vs. 0.235 ± 0.272, P < 0.001). This VA improvement was similar to control group (P = 0.052). In CS, there were significant differences in patient versus control groups (69.069% ± 70.235% vs. 27.215% ± 25.27%, P = 0.025). Linear regression showed that initial VA and CS function could not predict final VA (P = 0.183 and P = 0.138, respectively).CONCLUSIONS:Patients with optic neuritis showed decreased CS compared to control group which indicated the residual visual loss. Automated CS testing is useful in detecting residual visual loss in patients who recovered from optic neuritis.

Changes of tuning but not dynamics of contrast adaptation with age

Normal aging results in pronounced optical and neural changes in the visual system. Processes of adaptation are thought to help compensate for many of these changes in order to maintain perceptual constancy, but it is uncertain how stable adaptation itself remains with aging. We compared the dynamics of adaptation in young (aged 19–24 years) and older (aged 66–74) adults. Contrast thresholds for Gabor patterns were tracked during and after 300 s adaptation to vertical and horizontal Gabor patches. The time course of contrast adaptation and asymptotic adaptation magnitude were similar between older and young adults when normalized for their respective baseline thresholds. Older adults showed stronger transfer of adaptation to the orthogonal orientation and there was an asymmetry between the transfer of adaptation between the horizontal and vertical orientations for both groups. These results suggest age-related changes in orientation tuning while the processes of cortical contrast adaptation remain largely intact with aging.

Understanding implicit and explicit learning in adolescents with and without anorexia nervosa

BackgroundCognitive disturbances such as impairments in learning are thought to play a role in adult Anorexia Nervosa (AN). It is remains unclear to what extent these disturbances result from starvation of the brain, or relate to an abnormal premorbid cognitive profile. This study investigates learning processes in adolescents with AN, hypothesizing that implicit learning is intact, as found previously in explicit learning tasks. Secondly, we hypothesized that anxiety and depression symptoms, inherent to AN, are associated to learning processes in AN.MethodsIn total 46 adolescents diagnosed with AN and 44 control participants were administered an implicit category learning task in which they were asked to categorize simple perceptual stimuli (Gabor patches) based on a linear integration (i.e., an implicit task) of orientation and spatial frequency of the stimulus. A subgroup of adolescents (n = 38) also completed a task assessing explicit learning.ResultsModel-based analyses indicated that adolescents with AN performed significantly more accurately compared to their healthy peers regardless of whether they used the optimal strategy or not. Depression and anxiety did not relate to learning performance in the AN group.ConclusionsOverall, our findings of augmented implicit and explicit learning in adolescents with AN corroborate recent studies that suggested higher stimulus-response learning during prediction error paradigms. Learning disturbances in adult AN may then be at least partly due to long-term malnourishment, highlighting the importance of early recognition and refeeding in treatments for AN.

Temporal uncertainty enhances suppression of neural responses to predictable visual stimuli

Contextual information triggers predictions about the content (“what”) of environmental stimuli to update an internal generative model of the surrounding world. However, visual information dynamically changes across time, and temporal predictability (“when”) may influence the impact of internal predictions on visual processing. In this magnetoencephalography (MEG) study, we investigated how processing feature specific information (“what”) is affected by temporal predictability (“when”). Participants (N = 16) were presented with four consecutive Gabor patches (entrainers) with constant spatial frequency but with variable orientation and temporal onset. A fifth target Gabor was presented after a longer delay and with higher or lower spatial frequency that participants had to judge. We compared the neural responses to entrainers where the Gabor orientation could, or could not be temporally predicted along the entrainer sequence, and with inter-entrainer timing that was constant (predictable), or variable (unpredictable). We observed suppression of evoked neural responses in the visual cortex for predictable stimuli. Interestingly, we found that temporal uncertainty increased expectation suppression. This suggests that in temporally uncertain scenarios the neurocognitive system invests less resources in integrating bottom-up information. Multivariate pattern analysis showed that predictable visual features could be decoded from neural responses. Temporal uncertainty did not affect decoding accuracy for early visual responses, with the feature specificity of early visual neural activity preserved across conditions. However, decoding accuracy was less sustained over time for temporally jittered than for isochronous predictable visual stimuli. These findings converge to suggest that the cognitive system processes visual features of temporally predictable stimuli in higher detail, while processing temporally uncertain stimuli may rely more heavily on abstract internal expectations.

Contrast sensitivity and higher-order aberrations in Keratoconus subjects

This study analyzes the relationship between contrast-sensitivity and higher-order aberrations (HOA) in mild and subclinical-keratoconus in subjects with good visual-acuity (VA). Keratoconus group (including subclinical-keratoconus) and controls underwent autokeratometry, corneal-tomography, autorefraction and HOA measurement. Contrast-sensitivity was tested using a psychophysical two-alternative forced-choice Gabor patches in three blocks (6, 9, 12 cycles/deg). Controls were compared to the keratoconus group and to a keratoconus subgroup with VA of 0.00 LogMar group ("keratoconus-0.00VA"). Spearman correlation tested association between HOA and contrast-sensitivity. Twenty-two keratoconus subjects (38 eyes: 28 keratoconus, 10 subclinical-keratoconus, 20 keratoconus-0.00VA) and 35 controls were included. There was a significant difference between control and keratoconus, and between control and keratoconus-0.00VA, for keratometry, cylinder, thinnest and central corneal thickness (p < 0.001). Controls showed lower HOA and higher contrast-sensitivity for all spatial-frequencies (p < 0.001). Most HOA were negatively correlated with contrast-sensitivity for all spatial-frequencies for keratoconus group and for 9 and 12 cycles/deg for keratoconus-0.00VA. Keratoconus subjects with good VA showed reduction in contrast-sensitivity and increased HOAs compared to controls. HOA and contrast-sensitivity are inversely correlated in subjects with mild keratoconus despite good VA. This suggests that the main mechanism underlying the decreased vision quality in keratoconus is the increase of HOA.

A position anchor sinks the double-drift illusion.

When the internal texture of a Gabor patch moves orthogonally to its envelope's motion, the perceived path, viewed in the periphery, shifts dramatically in position, and direction relative to the true path (the double-drift illusion). Here, we examine positional uncertainty as a critical factor underlying this illusory shift. We presented participants with an anchoring line at different distances from the drifting Gabor's physical path. Our results indicate that placing an anchor (a fixed line) close to the Gabor's path halved the magnitude of the illusion. This suppression was symmetrical for anchors placed on either side of the Gabor. In a second experiment, we used crowding to degrade the anchoring line's position information by embedding it in a set of parallel lines. In this case, despite the presence of the same lines that reduced the illusion when presented in isolation, the illusory shift was now largely restored. We suggest that the adjacent lines crowded each other, reducing their positional certainty, and thus their ability to anchor the location of the moving Gabor. These findings indicate that the positional uncertainty of the equiluminant Gabor patch is critical for the illusory position offset.

Induced astigmatism biases the orientation information represented in multivariate electroencephalogram activities.

A small physical change in the eye influences the entire neural information process along the visual pathway, causing perceptual errors and behavioral changes. Astigmatism, a refractive error in which visual images do not evenly focus on the retina, modulates visual perception, and the accompanying neural processes in the brain. However, studies on the neural representation of visual stimuli in astigmatism are scarce. We investigated the relationship between retinal input distortions and neural bias in astigmatism and how modulated neural information causes a perceptual error. We induced astigmatism by placing a cylindrical lens on the dominant eye of human participants, while they reported the orientations of the presented Gabor patches. The simultaneously recorded electroencephalogram activity revealed that stimulus orientation information estimated from the multivariate electroencephalogram activity was biased away from the neural representation of the astigmatic axis and predictive of behavioral bias. The representational neural dynamics underlying the perceptual error revealed the temporal state transition; it was transiently dynamic and unstable (approximately 350 ms from stimulus onset) that soon stabilized. The biased stimulus orientation information represented by the spatially distributed electroencephalogram activity mediated the distorted retinal images and biased orientation perception in induced astigmatism.

Your Brain Knows if You’re Iron Deficient: Distinct Brain Dynamics in Iron Deficient vs. Sufficient Females in a Visual Category Learning Task

ObjectivesThe present study sought to determine the possibility of identifying someone as either iron deficient or sufficient based solely on brain activity, and, if possible, how quickly (based on processing time on a cognitive task) this could be done. MethodsBoth iron sufficient(IS) and iron deficient non-anemic (IDNA) females (mean age 21.1 y) learned two visual categorization tasks while concurrent EEG was acquired. Both tasks involved classifying gray-scale gabor patches on the basis of spatial frequency and orientation; one task used an easily-verbalized rule (rule-based, RB), the other required complex integration of the information (II). Moving windows (20 ms width) of EEG data from 100 electrodes were used to predict the participant’s iron status using logistic regression; model form was determined using stepwise variable selection. The outcome variable was the area under the curve (AUC) of the receiver operating characteristic for the classification. We set a criterion of AUC ≥ 0.80 for successful classification performance. ResultsFor both tasks, successful classification was possible before 200 ms of processing on the basis of fewer than 12 electrodes. Classification in the RB task suggested some early right lateralization in the selection of electrodes, which became more central as processing proceeded. Classification in the II task did not suggest lateralization, although there was some change to more central electrodes as processing proceeded. At each 20 ms time window, for each of the selected set of electrodes, a measure of neural efficiency was calculated as the ratio of the hazard function of the reaction time distribution and the global field power of the selected set of electrodes. This ratio can be interpreted as the amount of work accomplished per unit of energy expended. In all cases, neural efficiency for the IS females exceeded that for the IDNA females, suggesting that the efficiency with which neural energy is expended in cognitive work differs as a function of iron status. ConclusionsIron deficiency without anemia results in distinct patterns of brain activity early in processing that reflect reduced levels of neural efficiency, relative to females who are iron sufficient. Funding SourcesOU Office of the Vice President for Research.

Increased Visual Sensitivity and Occipital Activity in Patients With Hemianopia Following Vision Rehabilitation.

Hemianopia, loss of vision in half of the visual field, results from damage to the visual pathway posterior to the optic chiasm. Despite negative effects on quality of life, few rehabilitation options are currently available. Recently, several long-term training programs have been developed that show visual improvement within the blind field, although little is known of the underlying neural changes. Here, we have investigated functional and structural changes in the brain associated with visual rehabilitation. Seven human participants with occipital lobe damage enrolled in a visual training program to distinguish which of two intervals contained a drifting Gabor patch presented within the blind field. Participants performed ∼25 min of training each day for 3–6 months and undertook psychophysical tests and a magnetic resonance imaging scan before and after training. A control group undertook psychophysical tests before and after an equivalent period without training. Participants who were not at ceiling on baseline tests showed on average 9.6% improvement in Gabor detection, 8.3% in detection of moving dots, and 9.9% improvement in direction discrimination after training. Importantly, psychophysical improvement only correlated with improvement in Humphrey perimetry in the trained region of the visual field. Whole-brain analysis showed an increased neural response to moving stimuli in the blind visual field in motion area V5/hMT. Using a region-of-interest approach, training had a significant effect on the blood oxygenation level-dependent signal compared with baseline. Moreover, baseline V5/hMT activity was correlated to the amount of improvement in visual sensitivity using psychophysical and perimetry tests. This study, identifying a critical role for V5/hMT in boosting visual function, may allow us to determine which patients may benefit most from training and design adjunct interventions to increase training effects.SIGNIFICANCE STATEMENT Homonymous visual field loss is a common consequence of brain injury and is estimated to affect more than 230,000 people in the United Kingdom. Despite its high prevalence and well-described impact on quality of life, treatments to improve visual sensitivity remain experimental, and deficits are considered permanent after 6 months. Our study shows that behavioral changes following vision rehabilitation are associated with enhanced visually-evoked occipital activity to stimuli in the blind visual field. Unlike previous behavioral studies, we observe clinical changes that are specific to the trained region of vision. This lends significant weight to such training paradigms and offers a mechanism by which visual function can be improved despite damage to the primary visual pathway.

Feature Counting Is Impaired When Shifting Attention Between the Eyes in Adults With Amblyopia.

BackgroundFeature counting requires rapid shifts of attention in the visual field and reflects higher-level cortical functions. This process is drastically impaired in the amblyopic eye of strabismic amblyopes. In this study, we hypothesized that feature counting performance in anisometropic and strabismic amblyopes is further impaired when shifts in attention is required between the eyes.Materials and MethodsThrough a mirror stereoscope, highly visible Gabor patches were presented to the same eye within a block or randomly presented to the left eye or to the right eye with an equal probability within a block. The task was to report the number of Gabors (3 to 9) as accurately as possible. Counting performance was compared between the amblyopes and the normal-vision observers and between the viewing conditions (shifting attention between the eyes versus maintaining attention in the same eye).ResultsWhen attention was maintained in the same eye, the amblyopic eye of both anisometropic and strabismic groups undercounted the number of Gabors, but achieved near-perfect performance with their fellow eye, compared to normal-vision observers. In contrast, when shifting attention randomly to the left or to the right eye, the amblyopic eye further undercounted the number of Gabors. Undercounting was also found in the fellow eye of strabismic amblyopes, but was not in the fellow eye of anisometropic amblyopes. Performance in normal-vision observers did not differ between shifting attention between the eyes and maintaining attention in the same eye.ConclusionOur data showed that the amblyopic eye of both anisometropic and strabismic amblyopes further undercounted features when shifting attention between the eyes, compared to when maintaining attention in the same eye. This suggests that the ability to quickly redirect attention, particularly under interocular suppression, is impaired in amblyopia. The fellow eye of strabismic amblyopes also undercounted features when shifting attention between the eyes. However, such fellow eye abnormality was not found in anisometropic amblyopes, suggesting that different patterns of visual deficits are associated with amblyopia of different etiologies. The inability to count multiple features accurately reflects dysfunctions of high-level cortices in the amblyopic brain.

Visual Predictions Operate on Different Timescales.

Humans live in a volatile environment, subject to changes occurring at different timescales. The ability to adjust internal predictions accordingly is critical for perception and action. We studied this ability with two EEG experiments in which participants were presented with sequences of four Gabor patches, simulating a rotation, and instructed to respond to the last stimulus (target) to indicate whether or not it continued the direction of the first three stimuli. Each experiment included a short-term learning phase in which the probabilities of these two options were very different (p = .2 vs. p = .8, Rules A and B, respectively), followed by a neutral test phase in which both probabilities were equal. In addition, in one of the experiments, prior to the short-term phase, participants performed a much longer long-term learning phase where the relative probabilities of the rules predicting targets were opposite to those of the short-term phase. Analyses of the RTs and P3 amplitudes showed that, in the neutral test phase, participants initially predicted targets according to the probabilities learned in the short-term phase. However, whereas participants not pre-exposed to the long-term learning phase gradually adjusted their predictions to the neutral probabilities, for those who performed the long-term phase, the short-term associations were spontaneously replaced by those learned in that phase. This indicates that the long-term associations remained intact whereas the short-term associations were learned, transiently used, and abandoned when the context changed. The spontaneous recovery suggests independent storage and control of long-term and short-term associations.

Serial dependence does not originate from low-level visual processing

Perception depends not only on the current sensory input but also on the preceding history of stimuli. In serial dependence (SD), for example, the orientation of a Gabor patch is mistakenly reported as more similar to previous trials than it actually is. This bias is typically observed for moderate orientation differences (<45°) and extends over a few trials in the past. It is hotly debated whether SD originates at perceptual or post-perceptual, e.g., decisional, stages. Here, we provide evidence for the latter hypothesis. We presented Gabor patches with different spatial frequencies or Gabors intermingled with dot patterns. Even though stimuli were perceptually clearly dissimilar, we found robust SD effects arguing against any perceptual account. These findings suggest a re-evaluation of current models and theoretical accounts of SD.

Visual attention in spatial cueing and visual search.

To characterize internal processes of an observer conducting perceptual tasks, we developed an observer model that combines the perceptual template model (PTM), the attention mechanisms in the PTM framework (Lu & Dosher, 1998), and uncertainty of signal detection theory (Green & Swets, 1966). The model was evaluated with a visual search experiment conducted in a range of external noise, signal contrast, and target-distractor similarity conditions. In each trial, eight Gabor patches were shown in each of two brief intervals, with one target at a different orientation from the distractors in one of the presentations. Subjects were precued to a subset of the stimuli (1, 2, 4, or 8) and asked to report (a) which interval contained the target and (b) where the target was. Individual roles of uncertainty and of attention in visual search were investigated by comparing models with and without an attention component. The results showed that decision uncertainty alone was sufficient to account for the set-size effect, even in conditions with high target-distractor similarity. Our theoretical model and empirical results provide a coherent picture regarding how visual information is selected and processed during feature search.

Oculomotor inhibition during smooth pursuit and its dependence on contrast sensitivity.

Our eyes are never still, but tend to "freeze" in response to stimulus onset. This effect is termed “oculomotor inhibition” (OMI); its magnitude and time course depend on the stimulus parameters, attention, and expectation. We previously showed that the time course and duration of microsaccade and spontaneous eye-blink inhibition provide an involuntary measure of low-level visual properties such as contrast sensitivity during fixation. We investigated whether this stimulus-dependent inhibition also occurs during smooth pursuit, for both the catch-up saccades and the pursuit itself. Observers followed a target with continuous back-and-forth horizontal motion while a Gabor patch was briefly flashed centrally with varied spatial frequency and contrast. Catch-up saccades of the size of microsaccades had a similar pattern of inhibition as microsaccades during fixation, with stronger inhibition onset and faster inhibition release for more salient stimuli. Moreover, a similar stimulus dependency of inhibition was shown for pursuit latencies and peak velocity. Additionally, microsaccade latencies at inhibition release, peak pursuit velocities, and latencies at minimum pursuit velocity were correlated with contrast sensitivity. We demonstrated the generality of OMI to smooth pursuit for both microsaccades and the pursuit itself and its close relation to the low-level processes that define saliency, such as contrast sensitivity.

Human Sensory Cortex Contributes to the Long-Term Storage of Aversive Conditioning.

Growing animal data evince a critical role of the sensory cortex in the long-term storage of aversive conditioning, following acquisition and consolidation in the amygdala. Whether and how this function is conserved in the human sensory cortex is nonetheless unclear. We interrogated this question in a human aversive conditioning study using multidimensional assessments of conditioning and long-term (15 d) retention. Conditioned stimuli (CSs; Gabor patches) were calibrated to differentially activate the parvocellular (P) and magnocellular (M) visual pathways, further elucidating cortical versus subcortical mechanisms. Full-blown conditioning and long-term retention emerged for M-biased CS (vs limited effects for P-biased CS), especially among anxious individuals, in all four dimensions assessed: threat appraisal (threat ratings), physiological arousal (skin conductance response), perceptual learning [discrimination sensitivity (d') and response speed], and cortical plasticity [visual evoked potentials (VEPs) and cortical current density]. Interestingly, while behavioral, physiological, and VEP effects were comparable at immediate and delayed assessments, the cortical substrates evolved markedly over time, transferring from high-order cortices [inferotemporal/fusiform cortex and orbitofrontal cortex (OFC)] immediately to the primary and secondary visual cortex after the delay. In sum, the contrast between P- and M-biased conditioning confirms privileged conditioning acquisition via the subcortical pathway while the immediate cortical plasticity lends credence to the triadic amygdala-OFC-fusiform network thought to underlie threat processing. Importantly, long-term retention of conditioning in the basic sensory cortices supports the conserved role of the human sensory cortex in the long-term storage of aversive conditioning.SIGNIFICANCE STATEMENT A growing network of neural substrates has been identified in threat learning and memory. The sensory cortex plays a key role in long-term threat memory in animals, but such a function in humans remains unclear. To explore this problem, we conducted multidimensional assessments of immediate and delayed (15 d) effects of human aversive conditioning. Behavioral, physiological, and scalp electrophysiological data demonstrated conditioning effects and long-term retention. High-density EEG intracranial source analysis further revealed the cortical underpinnings, implicating high-order cortices immediately and primary and secondary visual cortices after the long delay. Therefore, while high-order cortices support aversive conditioning acquisition (i.e., threat learning), the human sensory cortex (akin to the animal homolog) underpins long-term storage of conditioning (i.e., long-term threat memory).

Contribution of the slow motion mechanism to global motion revealed by an MAE technique

Two different motion mechanisms have been identified with motion aftereffect (MAE). (1) A slow motion mechanism, accessed by a static MAE, is sensitive to high-spatial and low-temporal frequency; (2) a fast motion mechanism, accessed by a flicker MAE, is sensitive to low-spatial and high-temporal frequency. We examined their respective responses to global motion after adapting to a global motion pattern constructed of multiple compound Gabor patches arranged circularly. Each compound Gabor patch contained two gratings at different spatial frequencies (0.53 and 2.13 cpd) drifting in opposite directions. The participants reported the direction and duration of the MAE for a variety of global motion patterns. We discovered that static MAE durations depended on the global motion patterns, e.g., longer MAE duration to patches arranged to see rotation than to random motion (Exp 1), and increase with global motion strength (patch number in Exp 2). In contrast, flicker MAEs durations are similar across different patterns and adaptation strength. Further, the global integration occurred at the adaptation stage, rather than at the test stage (Exp 3). These results suggest that slow motion mechanism, assessed by static MAE, integrate motion signals over space while fast motion mechanisms do not, at least under the conditions used.

Microsaccades mediate perceptual alternations in Monet\u2019s \u201cImpression, sunrise\u201d

Troxler fading, the perceptual disappearance of stationary images upon sustained fixation, is common for objects with equivalent luminance to that of the background. Previous work showed that variations in microsaccadic rates underlie the perceptual vanishing and intensification of simple stimuli, such as Gabor patches. Here, we demonstrate that microsaccade dynamics also contribute to Troxler fading and intensification during the viewing of representational art. Participants fixated a small spot while viewing either a Gabor patch on a blank background, or Monet’s painting “Impression, Sunrise.” They continuously reported, via button press/release, whether the Gabor patch, or the sun in Monet’s painting, was fading versus intensifying, while their eye movements were recorded with high precision. Microsaccade rates peaked before reports of increased visibility, and dropped before reports of decreased visibility or fading, both when viewing Gabor patches and Monet’s sun. These results reveal that the relationship between microsaccade production and the reversal and prevention of Troxler fading applies not only to the viewing of contrived stimuli, but also to the observation of “Impression, Sunrise.” Whether or not perceptual fading was consciously intended by Monet, our findings indicate that observers’ oculomotor dynamics are a contributor to the cornerstone of Impressionism.

Contrast Rivalry Paradigm Reveals Suppression of Monocular Input in Keratoconus

PurposeKeratoconus results in image quality loss in one or both eyes due to increased corneal distortion. This study quantified the depth of monocular suppression in keratoconus due to this image quality loss using a binocular contrast rivalry paradigm.MethodsContrast rivalry was induced in 50 keratoconic cases (11–31 years) and 12 age-matched controls by dichoptically viewing orthogonal Gabor patches of 5 cycles per degree (cpd) and 1.5 cpd spatial frequency for 120 seconds with their best-corrected spectacles and rigid gas permeable (RGP) contact lenses. The dwell time on each eye's percept was determined at baseline (100% contrast bilaterally) and at varying contrast levels (80–2.5%) in the stronger eye of keratoconus or dominant eye of controls. The contrast reduction needed in the stronger eye to balance dwell times on both eyes was considered a measure of suppression depth.ResultsAt baseline with 5 cpd stimuli and spectacle correction, the rivalry switches were less frequent and biased toward the stronger eye of cases, all relative to controls (P < 0.001). The contrast balance point of cases (20.51% [10.7–61%]) was lower than the controls (99.80% [98.6–100%]; P < 0.001) and strongly associated with the overall and interocular difference in disease severity (r = 0.83, P < 0.001). The suppression depth reduced for 1.5 cpd (70.8% [21.7–94%]), relative to 5 cpd stimulus (P < 0.001) and with contact lenses (80.1% [49.5–91.7%]), relative to spectacles (P < 0.001).ConclusionsThe eye with lesser disease severity dominates binocular viewing in keratoconus. The suppression depth of the poorer eye depends on the extent of bilateral disease severity, optical correction modality, and the target spatial frequency.