Jumpy and Jerky: When Peripheral Vision Faces Reverse-Phi

When an annulus in fast apparent motion reverses its contrast over time, the foveal and peripheral percepts are strikingly different. In central vision, the annulus appears to follow the same path as an annulus without flicker, whereas in the periphery, the stimulus seems to randomly jump across the screen. The illusion strength depends on motion speed and reversal rate. Our observations suggest that it results from a balance between conflicting phi and reverse-phi motion, positional uncertainty, and attention. In addition to illustrating the differences between central and peripheral motion processing, this illusion shows that both discrete positional sampling and motion energy combine to generate motion percepts, although with eccentricity dependent weights that are themselves affected by attention.

Encoding perceptual ensembles during visual search in peripheral vision

Observers can learn complex statistical properties of visual ensembles, such as their probability distributions. Even though ensemble encoding is considered critical for peripheral vision, whether observers learn such distributions in the periphery has not been studied. Here, we used a visual search task to investigate how the shape of distractor distributions influences search performance and ensemble encoding in peripheral and central vision. Observers looked for an oddly oriented bar among distractors taken from either uniform or Gaussian orientation distributions with the same mean and range. The search arrays were either presented in the foveal or peripheral visual fields. The repetition and role reversal effects on search times revealed observers' internal model of distractor distributions. Our results showed that the shape of the distractor distribution influenced search times only in foveal, but not in peripheral search. However, role reversal effects revealed that the shape of the distractor distribution could be encoded peripherally depending on the interitem spacing in the search array. Our results suggest that, although peripheral vision might rely heavily on summary statistical representations of feature distributions, it can also encode information about the distributions themselves.

Mapping the Contrast Sensitivity of the Visual Field With Bayesian Adaptive qVFM

Current clinical evaluation, which focuses on central vision, could be improved through characterization of residual vision with peripheral testing of visual acuity, contrast sensitivity, color vision, crowding, and reading speed. Assessing visual functions in addition to light sensitivity, a comprehensive visual field map (VFM) would be valuable for detecting and managing eye diseases. In a previous study, we developed a Bayesian adaptive qVFM method that combines a global module for preliminary assessment of the VFM's shape and a local module for assessment at individual retinal locations. The method was validated in measuring the light sensitivity VFM. In this study, we extended the qVFM method to measure contrast sensitivity across the visual field. In both simulations and psychophysics, we sampled 64 visual field locations (48 x 48 deg) and compared the qVFM method with a procedure that tested each retinal location independently (qFC; Lesmes et al., 2015). In each trial, subjects were required to identify a single optotype (size: 2.5 x 2.5 deg), one of 10 filtered Sloan letters. To compare the accuracy and precision of the two methods, three simulated eyes were tested in 1,280 trials with each method. In addition, data were collected from 10 eyes (5 OS, 5 OD) of five normal observers. For simulations, the average RMSE of the estimated contrast sensitivity with the qVFM and qFC methods were 0.057 and 0.100 after 320 trials, and 0.037 and 0.041 after 1,280 trials [all in log10 units, represent as log(sensitivity)], respectively. The average SD of the qVFM and qFC estimates were 0.054 and 0.096 after 320 trials, and 0.032 and 0.041 after 1,280 trials, respectively. The within-run variability (68.2% HWCIs) were comparable to the cross-run variability (SD). In the psychophysics experiment, the average HWCI of the estimated contrast sensitivity from the qVFM and qFC methods across the visual field decreased from 0.33 on the first trial to 0.072 and 0.16 after 160, and to 0.060 and 0.10 after 320 trials. The RMSE between the qVFM and qFC estimates started at 0.26, decreased to 0.12 after 160 and to 0.11 after 320 qVFM trials. The qVFM provides an accurate, precise, and efficient mapping of contrast sensitivity across the entire visual field. The method might find potential clinical applications in monitoring vision loss, evaluating therapeutic interventions, and developing effective rehabilitation for visual diseases.

Invisible Adaptation: The Effect of Awareness on the Strength of the Motion Aftereffect

The ability to process information despite the lack of perceptual awareness is one of the most fascinating aspects of the visual system. Such unconscious processing is often investigated using adaptation, where any presence of the former can be traced by its footprint on aftereffects following the latter. We have investigated the mechanisms of the motion aftereffect (MAE) using random dot displays of varying motion coherence as well as crowding to modulate both the physical as well as the perceptual strength of the adaptation stimulus. Perceptual strength was quantitatively measured as the performance in a forced-choice direction-discrimination task. A motion-nulling technique was used to quantitatively measure the strength of the MAE. We show that the strength of the dynamic MAE is independently influenced by both the physical stimulus strength as well as the subjective perceptual strength, with the effect of the former being more prominent than that of the latter. We further show that the MAE still persists under conditions of subthreshold perception. Our results suggest that perceptual awareness can influence the strength of visual processing, but the latter is not fully dependent on the former and can still take place at its partial or even total absence.

The Flip Tilt Illusion: Visible in Peripheral Vision as Predicted by the Central-Peripheral Dichotomy

Consider a gray field comprising pairs of vertically aligned dots; in each pair, one dot is white the other black. When viewed in a peripheral visual field, these pairs appear horizontally aligned. By the Central-Peripheral Dichotomy, this flip tilt illusion arises because top-down feedback from higher to lower visual cortical areas is too weak or absent in the periphery to veto confounded feedforward signals from the primary visual cortex (V1). The white and black dots in each pair activate, respectively, on and off subfields of V1 neural receptive fields. However, the sub-fields' orientations, and the preferred orientations, of the most activated neurons are orthogonal to the dot alignment. Hence, V1 reports the flip tilt to higher visual areas. Top-down feedback vetoes such misleading reports, but only in the central visual field.

'The last channel': vision at the temporal margin of the field

The human visual field, on the temporal side, extends to at least 90° from the line of sight. Using a two-alternative forced-choice procedure in which observers are asked to report the direction of motion of a Gabor patch, and taking precautions to exclude unconscious eye movements in the direction of the stimulus, we show that the limiting eccentricity of image-forming vision can be established with precision. There are large, but reliable, individual differences in the limiting eccentricity. The limiting eccentricity exhibits a dependence on log contrast; but it is not reduced when the modulation visible to the rods is attenuated, a result compatible with the histological evidence that the outermost part of the retina exhibits a high density of cones. Our working hypothesis is that only one type of neural channel is present in the far periphery of the retina, a channel that responds to temporally modulated stimuli of low spatial frequency and that is directionally selective.

Retinal Periphery Is Insensitive to Sudden Transient Motion

Peripherally viewed targets moved around against a background of random dynamic noise. Slow movements were visible, fast movements were not. Thus, a target that repetitively drifted to the right and snapped back appeared to drift endlessly to the right with no visible snapbacks.

Seven Myths on Crowding and Peripheral Vision

Crowding has become a hot topic in vision research, and some fundamentals are now widely agreed upon. For the classical crowding task, one would likely agree with the following statements. (1) Bouma's law can be stated, succinctly and unequivocally, as saying that critical distance for crowding is about half the target's eccentricity. (2) Crowding is predominantly a peripheral phenomenon. (3) Peripheral vision extends to at most 90° eccentricity. (4) Resolution threshold (the minimal angle of resolution) increases strongly and linearly with eccentricity. Crowding increases at an even steeper rate. (5) Crowding is asymmetric as Bouma has shown. For that inner-outer asymmetry, the peripheral flanker has more effect. (6) Critical crowding distance corresponds to a constant cortical distance in primary visual areas like V1. (7) Except for Bouma's seminal article in 1970, crowding research mostly became prominent starting in the 2000s. I propose the answer is "not really" or "not quite" to these assertions. So should we care? I think we should, before we write the textbook chapters for the next generation.

Dissociable effects of visual crowding on the perception of color and motion

Our ability to recognize objects in peripheral vision is fundamentally limited by crowding, the deleterious effect of clutter that disrupts the recognition of features ranging from orientation and color to motion and depth. Previous research is equivocal on whether this reflects a singular process that disrupts all features simultaneously or multiple processes that affect each independently. We examined crowding for motion and color, two features that allow a strong test of feature independence. "Cowhide" stimuli were presented 15° in peripheral vision, either in isolation or surrounded by flankers to give crowding. Observers reported either the target direction (clockwise/counterclockwise from upward) or its hue (blue/purple). We first established that both features show systematic crowded errors (biased predominantly toward the flanker identities) and selectivity for target-flanker similarity (with reduced crowding for dissimilar target/flanker elements). The multiplicity of crowding was then tested with observers identifying both features. Here, a singular object-selective mechanism predicts that when crowding is weak for one feature and strong for the other that crowding should be all-or-none for both. In contrast, when crowding was weak for color and strong for motion, errors were reduced for color but remained for motion, and vice versa with weak motion and strong color crowding. This double dissociation reveals that crowding disrupts certain combinations of visual features in a feature-specific manner, ruling out a singular object-selective mechanism. Thus, the ability to recognize one aspect of a cluttered scene, like color, offers no guarantees for the correct recognition of other aspects, like motion.

The Effect of Simulated Visual Field Loss on Optokinetic Nystagmus

Purpose

Assessment of functional vision across the visual field is hampered by a reliance on patients' subjective judgement of the presence of a stimulus, and the accompanying demands (time and attention) this places on them. As a first step toward determining whether an objective measure of an involuntary eye movement (optokinetic nystagmus [OKN]) could provide an objective measure of field loss, we determined how various measures of OKN depend on the extent of simulated visual field loss (SVFL).

Methods

We used infrared eye-tracking to measure the eye movements of 16 healthy participants viewing horizontally translating 2-dimensional noise patterns over trials of varying contrasts and different levels of SVFL. We quantified the strength of OKN by estimating the velocity of tracking eye movements compared to the stimulus (OKN gain). These measurements were made using an open-loop SVFL paradigm, where a varying amount of gaze-contingent peripheral stimuli was occluded.

Results

Full-field stimulation led to an average OKN gain of 0.92 ± 0.15. This value fell steadily with increasing SVFL to a value of 0.38 ± 0.20 when the periphery was not stimulated at all (i.e., the stimulus was a 5-deg. diameter foveal patch). We note considerable individual variation in OKN gain in all conditions.

Conclusions

Measuring the extent of visual field loss using an objective measure of OKN gain is feasible.

Translational Relevance

Simulated visual field loss reduces optokinetic nystagmus, but further refinement of this technique would be required to overcome individual differences and to pick up clinically relevant field defects.

Lower sensitivity to peripheral hypermetropic defocus due to higher order ocular aberrations

PURPOSE

Many myopia control interventions are designed to induce myopic relative peripheral refraction. However, myopes tend to show asymmetries in their sensitivity to defocus, seeing better with hypermetropic rather than myopic defocus. This study aims to determine the influence of chromatic aberrations (CA) and higher-order monochromatic aberrations (HOA) in the peripheral asymmetry to defocus.

METHODS

Peripheral (20° nasal visual field) low-contrast (10%) resolution acuity of nine subjects (four myopes, four emmetropes, one hypermetrope) was evaluated under induced myopic and hypermetropic defocus between ±5 D, under four conditions: (a) Peripheral Best Sphere and Cylinder (BSC) correction in white light; (b) Peripheral BSC correction + CA elimination (green light); (c) Peripheral BSC correction + HOA correction in white light; and (d) Peripheral BSC correction + CA elimination + HOA correction. No cycloplegia was used, and all measurements were repeated three times.

RESULTS

The slopes of the peripheral acuity as a function of positive and negative defocus differed, especially when the natural HOA and CA were present. This asymmetry was quantified as the average of the absolute sum of positive and negative defocus slopes for all subjects (AVS). The AVS was 0.081 and 0.063 logMAR/D for white and green light respectively, when the ocular HOA were present. With adaptive optics correction for HOA, the asymmetry reduced to 0.021 logMAR/D for white and 0.031 logMAR/D for green light, mainly because the sensitivity to hypermetropic defocus increased when HOA were corrected.

CONCLUSION

The asymmetry was only slightly affected by the elimination of the CA of the eye, whereas adaptive optics correction for HOA reduced the asymmetry. The HOA mainly affected the sensitivity to hypermetropic defocus.

In the corner of the eye: camouflaging motion in the peripheral visual field

Most animals need to move, and motion will generally break camouflage. In many instances, most of the visual field of a predator does not fall within a high-resolution area of the retina and so, when an undetected prey moves, that motion will often be in peripheral vision. We investigate how this can be exploited by prey, through different patterns of movement, to reduce the accuracy with which the predator can locate a cryptic prey item when it subsequently orients towards a target. The same logic applies for a prey species trying to localize a predatory threat. Using human participants as surrogate predators, tasked with localizing a target on peripherally viewed computer screens, we quantify the effects of movement (duration and speed) and target pattern. We show that, while motion is certainly detrimental to camouflage, should movement be necessary, some behaviours and surface patterns reduce that cost. Our data indicate that the phenotype that minimizes localization accuracy is unpatterned, having the mean luminance of the background, does not use a startle display prior to movement, and has short (below saccadic latency), fast movements.

Effects of an Active Visuomotor Steering Task on Covert Attention

In complex dynamic tasks such as driving it is essential to be aware of potentially important targets in peripheral vision. While eye tracking methods in various driving tasks have provided much information about drivers’ gaze strategies, these methods only inform about overt attention and provide limited grounds to assess hypotheses concerning covert attention. We adapted the Posner cue paradigm to a dynamic steering task in a driving simulator. The participants were instructed to report the presence of peripheral targets while their gaze was fixed to the road. We aimed to see whether and how the active steering task and complex visual stimulus might affect directing covert attention to the visual periphery. In a control condition, the detection task was performed without a visual scene and active steering. Detection performance in bends was better in the control task compared to corresponding performance in the steering task, indicating that active steering and the complex visual scene affected the ability to distribute covert attention. Lower targets were discriminated slower than targets at the level of the fixation circle in both conditions. We did not observe higher discriminability for on-road targets. The results may be accounted for by either bottom-up optic flow biasing of attention, or top-down saccade planning.

Inflation versus filling-in: why we feel we see more than we actually do in peripheral vision

Do we perceive fine details in the visual periphery? Here, we propose that phenomenology in the visual periphery can be characterized by an inflated sense of perceptual capacity, as observers overestimate the quality of their perceptual inputs. Distinct from the well-known perceptual phenomenon of 'filling-in' where perceptual content is generated or completed endogenously, inflation can be characterized by incorrect introspection at the subjective level. The perceptual content itself may be absent or weak (i.e. not necessarily filled-in), and yet such content is mistakenly regarded by the system as rich. Behaviourally, this can be reflected by metacognitive deficits in the degree to which confidence judgements track task accuracy, and decisional biases for observers to think particular items are present, even when they are not. In two experiments using paradigms that exploit unique attributes of peripheral vision (crowding and summary statistics), we provide evidence that both types of deficits are present in peripheral vision, as observers' reports are marked by overconfidence in discrimination judgements and high numbers of false alarms in detection judgements. We discuss potential mechanisms that may be the cause of inflation and propose future experiments to further explore this unique sensory phenomenon.This article is part of the theme issue 'Perceptual consciousness and cognitive access'.

Exploring the Extent in the Visual Field of the Honeycomb and Extinction Illusions

There are situations in which what is perceived in central vision is different to what is perceived in the periphery, even though the stimulus display is uniform. Here, we studied two cases, known as the Extinction illusion and the Honeycomb illusion, involving small disks and lines, respectively, presented over a large extent of the visual field. Disks and lines are visible in the periphery on their own, but they become invisible when they are presented as part of a pattern (grid). Observers (N = 56) adjusted a circular probe to report the size of the region in which they had seen the lines or the disks. Different images had black or white lines/disks, and we included control stimuli in which these features were spatially separated from the regular grid of squares. We confirmed that the illusion was experienced by the majority of observers and is dependent on the interaction between the elements (i.e., the lines/disks have to be near the squares). We found a dissociation between the two illusions in the dependence on contrast polarity suggesting different mechanisms. We analysed the variability between individuals with respect to schizotypical and autistic-spectrum traits (short version of the Oxford-Liverpool Inventory of Feelings and Experiences [O-LIFE] questionnaire and the Autistic Quotient, respectively) but found no significant relationships. We discuss how illusions relative to what observers are aware of in the periphery may offer a unique tool to study visual awareness.

Challenges to pooling models of crowding: Implications for visual mechanisms

A set of phenomena known as crowding reveal peripheral vision's vulnerability in the face of clutter. Crowding is important both because of its ubiquity, making it relevant for many real-world tasks and stimuli, and because of the window it provides onto mechanisms of visual processing. Here we focus on models of the underlying mechanisms. This review centers on a popular class of models known as pooling models, as well as the phenomenology that appears to challenge a pooling account. Using a candidate high-dimensional pooling model, we gain intuitions about whether a pooling model suffices and reexamine the logic behind the pooling challenges. We show that pooling mechanisms can yield substitution phenomena and therefore predict better performance judging the properties of a set versus a particular item. Pooling models can also exhibit some similarity effects without requiring mechanisms that pool at multiple levels of processing, and without constraining pooling to a particular perceptual group. Moreover, we argue that other similarity effects may in part be due to noncrowding influences like cuing. Unlike low-dimensional straw-man pooling models, high-dimensional pooling preserves rich information about the stimulus, which may be sufficient to support high-level processing. To gain insights into the implications for pooling mechanisms, one needs a candidate high-dimensional pooling model and cannot rely on intuitions from low-dimensional models. Furthermore, to uncover the mechanisms of crowding, experiments need to separate encoding from decision effects. While future work must quantitatively examine all of the challenges to a high-dimensional pooling account, insights from a candidate model allow us to conclude that a high-dimensional pooling mechanism remains viable as a model of the loss of information leading to crowding.

The Role of Emotional Expression and Eccentricity on Gaze Perception

The perception of another’s gaze direction and facial expression complements verbal communication and modulates how we interact with other people. However, our perception of these two cues is not always accurate, even when we are looking directly at the person. In addition, in many cases social communication occurs within groups of people where we can’t always look directly at every person in the group. Here, we sought to examine how the presence of other people influences our perception of a target face. We asked participants to judge the direction of gaze of the target face as either looking to their left, to their right or directly at them, when the face was viewed on its own or viewed within a group of other identity faces. The target face either had an angry or a neutral expression and was viewed directly (foveal experiment), or within peripheral vision (peripheral experiment). When the target was viewed within a group, the flanking faces also had either neutral or angry expressions and their gaze was in one of five different directions (from averted leftwards to averted rightwards in steps of 10°). When the target face was viewed foveally there was no effect of target emotion on participants’ judgments of its gaze direction. There was also no effect of the presence of flankers (regardless of expression) on the perception of the target gaze. When the target face was viewed peripherally, participants judged its direction of gaze to be direct over a wider range of gaze deviations than when viewed foveally, and more so for angry faces than neutral faces. We also find that flankers (regardless of emotional expression) did not influence performance. This suggests that observers judge that angry faces were looking at them over a broad range of gaze deviations in the periphery only, possibly resulting from increased uncertainty about the stimulus.

Dynamics of contrast adaptation in central and peripheral vision

Adaptation aftereffects are generally stronger for peripheral than for foveal viewing. We examined whether there are also differences in the dynamics of visual adaptation in central and peripheral vision. We tracked the time course of contrast adaptation to binocularly presented Gabor patterns in both the central visual field (within 5°) and in the periphery (beyond 10° eccentricity) using a yes/no detection task to monitor contrast thresholds. Consistent with previous studies, sensitivity losses were stronger in the periphery than in the center when adapting to equivalent high contrast (90% contrast) patterns. The time course of the threshold changes was fitted with separate exponential functions to estimate the time constants during the adapt and post-adapt phases. When adapting to equivalent high contrast, adaptation effects built up and decayed more slowly in the periphery compared with central adaptation. Surprisingly, the aftereffect in the periphery did not decay completely to the baseline within the monitored post-adapt period (400 s), and instead asymptoted to a higher level than for central adaptation. Even when contrast was reduced to one-third (30% contrast) of the central contrast, peripheral adaptation remained stronger and decayed more slowly. This slower dynamic was also confirmed at suprathreshold test contrasts by tracking tilt-aftereffects with a 2AFC orientation discrimination task. Our results indicate that the dynamics of contrast adaptation differ between central and peripheral vision, with the periphery adapting not only more strongly but also more slowly, and provide another example of potential qualitative processing differences between central and peripheral vision.

Gaze Cuing Effects in Peripheral Vision

When we see another person’s gaze, spatial attention shifts toward the gaze direction. Thus, a gaze perceiver can more quickly respond to a forthcoming target when it appears in a direction of a gaze giver than when it does not. This phenomenon is termed the gaze cuing effect. Previous studies have investigated the gaze cuing effect only in foveal vision; hence, it remains unclear whether the gaze cuing effect is induced when a face is presented in peripheral vision. This is an important issue because in our daily lives we communicate not only with people in front of us but also with those in our periphery. To tackle this question, we manipulated vertically aligned locations of a facial stimulus (i.e., a face stimulus appeared above or below the center fixation) and tested the extent to which a gaze cuing effect, conveyed by gaze shifts of another, is observed in the periphery. The facial stimulus was located 0, ±2.5, ±5.0, and ±7.5° of the visual angle from the center of the display, and a target was presented 5.6° to the left or right of the center of the display. In Experiment 1, when participants responded to the location of an abrupt onset of a target (i.e., localization task), we observed significant gaze cuing effects when a facial stimulus was located 0, ±2.5, and ±5.0°, but not ±7.5°. In Experiment 2, we replicated the findings in Experiment 1 if participants pressed a key only when a target appeared (i.e., detection task). In Experiment 3, we used adjusted sizes of facial images based on the cortical representations and manipulated eye directions of the facial images oriented toward the possible target locations; it resulted in enlarged effective field of view for gaze cuing effects. The study reveals that gaze cuing effects can appear even in peripheral vision and within a vertical distance of 5.0° of the visual angles, but the effective field of view is expanded when the facial image is adjusted based on the cortical representations, and eye gaze directly looks at the possible target locations.

Influence of Multiple Types of Proximity on the Degree of Visual Crowding Effects Within a Single Gap Detection Task

The visual system cannot recognize an object (target) in peripheral vision when presented with neighboring similar stimuli (flanker). This object recognition disability is known as crowding. Studies have shown that various types of proximity, such as spatial distance or semantic category, affect the degree of crowding. However, thus far, these effects have mostly been studied separately. Hence, their underlying similarities and differences are still unknown. In this study, we developed a novel gap detection task and tested whether the effect of three different types of proximity in crowding (the relative position between target gap and nearest flanker edge, the flanker location compared with the target location, and the semantic category of the target) can be measured within a single task. A psychometric function analysis revealed that two of the assumed types of proximity affected the degree of crowding within a single task.

Cortical Reorganization of Peripheral Vision Induced by Simulated Central Vision Loss

When one's central vision is deprived, a spared part of the peripheral retina acts as a pseudofovea for fixation. The neural mechanisms underlying this compensatory adjustment remain unclear. Here we report cortical reorganization induced by simulated central vision loss. Human subjects of both sexes learned to place the target at an eccentric retinal locus outside their blocked visual field for object tracking. Before and after training, we measured visual crowding-a bottleneck of object identification in peripheral vision, using psychophysics and fMRI. We found that training led to an axis-specific reduction of crowding. The change of the crowding effect was reflected in the change of BOLD signal, as a release of cortical suppression in multiple visual areas starting as early as V1. Our findings suggest that the adult visual system is capable of reshaping its oculomotor control and sensory coding to adapt to impoverished visual input.SIGNIFICANCE STATEMENT By simulating central vision loss in normally sighted adults, we found that oculomotor training not only induces PRL, but also facilitates form processing in peripheral vision. As subjects learned to place the target at an eccentric retinal locus, "visual crowding"-the detrimental effect of clutter on peripheral object identification-was reduced. The reduction of the crowding effect was accompanied by a release of response suppression in the visual cortex. These findings indicate that the adult visual system is capable of reshaping the peripheral vision to adapt to central vision loss.

The role of Peripheral Vision in the Flashed Face Distortion Effect

The flashed face distortion effect is a phenomenon whereby images of faces, presented at 4-5 Hz in the visual periphery, appear distorted. It has been hypothesized that the effect is driven by cortical, rather than retinal, components. Here, we investigated the role of peripheral viewing on the effect. Normally sighted participants viewed the stimulus peripherally, centrally, and centrally with a blurring lens (to match visual acuity in the peripheral location). Participants rated the level of distortion using a Visual Analogue Scale. Although optical defocus did have a significant effect on distortion ratings, peripheral viewing had a much greater effect, despite matched visual acuity. We suggest three potential mechanisms for this finding: increased positional uncertainty in the periphery, reduced deployment of attention to the visual periphery, or the visual crowding effect.

The role of peripheral vision in vertical road sign identification and discrimination

The role of peripheral vision in road sign identification and discrimination was investigated in two studies. Peripheral vision plays an important role in road signs perception due to their lateral positioning. In the first study 20 participants identified road signs presented at five levels of horizontal eccentricity (1.1°-12.4°), and two levels of vertical eccentricity (0°-2.5°). In the second study road sign discrimination was tested in a same-different discrimination task. The first study showed that a vertical offset of 2.5° degraded proportion correct rate by 9%. Proportion correct rate decreased from 79% to 41% in the transition from 1.1° to 12.4° of horizontal offset. The second study showed an accurate discrimination for road signs presented within a horizontal offset of 6.4°. Road signs with angular shapes and prominent vertexes as triangular or cross signs were better identified in peripheral vision than signs with more compact shapes (circular signs). Practitioner summary: Vertical road signs, due to their lateral positioning, are often perceived in peripheral vision. Horizontal and vertical eccentricity negatively impacts the driver's ability to correctly identify and discriminate traffic signs. The use of singular shapes and a design with simple pictograms and large contrasting areas strongly facilitate road sign perception in peripheral vision.

The Illusion of Uniformity Does Not Depend on the Primary Visual Cortex: Evidence From Sensory Adaptation

Visual experience appears richly detailed despite the poor resolution of the majority of the visual field, thanks to foveal-peripheral integration. The recently described uniformity illusion (UI), wherein peripheral elements of a pattern take on the appearance of foveal elements, may shed light on this integration. We examined the basis of UI by generating adaptation to a pattern of Gabors suitable for producing UI on orientation. After removing the pattern, participants reported the tilt of a single peripheral Gabor. The tilt aftereffect followed the physical adapting orientation rather than the global orientation perceived under UI, even when the illusion had been reported for a long time. Conversely, a control experiment replacing illusory uniformity with a physically uniform Gabor pattern for the same durations did produce an aftereffect to the global orientation. Results indicate that UI is not associated with changes in sensory encoding at V1 but likely depends on higher level processes.

Binocular contrast summation and inhibition depends on spatial frequency, eccentricity and binocular disparity

PURPOSE

When central vision is compromised, visually-guided behaviour becomes dependent on peripheral retina, often at a preferred retinal locus (PRL). Previous studies have examined adaptation to central vision loss with monocular 2D paradigms, whereas in real tasks, patients make binocular eye movements to targets of various sizes and depth in 3D environments.

METHODS

We therefore examined monocular and binocular contrast sensitivity functions with a 26-AFC (alternate forced choice) band-pass filtered letter identification task at 2° or 6° eccentricity in observers with simulated central vision loss. Binocular stimuli were presented in corresponding or non-corresponding stereoscopic retinal locations. Gaze-contingent scotomas (0.5° radius disks of pink noise) were simulated independently in each eye with a 1000 Hz eye tracker and 120 Hz dichoptic shutter glasses.

RESULTS

Contrast sensitivity was higher for binocular than monocular conditions, but only exceeded probability summation at low-mid spatial frequencies in corresponding retinal locations. At high spatial frequencies or non-corresponding retinal locations, binocular contrast sensitivity showed evidence of interocular suppression.

CONCLUSIONS

These results suggest that binocular vision deficits may be underestimated by monocular vision tests and identify a method that can be used to select a PRL based on binocular contrast summation.