Asymmetries around the visual field: From retina to cortex to behavior
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Abstract Visual performance varies around the visual field. It is best near the fovea compared to the periphery, and at iso-eccentric locations it is best on the horizontal, intermediate on the lower, and poorest on the upper meridian. The fovea-to-periphery performance decline is linked to the decreases in cone density, retinal ganglion cell (RGC) density, and V1 cortical magnification factor (CMF) as eccentricity increases. The origins of polar angle asymmetries are not well understood. Optical quality and cone density vary across the retina, but recent computational modeling has shown that these factors can only account for a small percentage of behavior. Here, we investigate how visual processing beyond the cone photon absorptions contributes to polar angle asymmetries in performance. First, we quantify the extent of asymmetries in cone density, midget RGC density, and V1 CMF. We find that both polar angle asymmetries and eccentricity gradients increase from cones to mRGCs, and from mRGCs to cortex. Second, we extend our previously published computational observer model to quantify the contribution of phototransduction by the cones and spatial filtering by mRGCs to behavioral asymmetries. Starting with photons emitted by a visual display, the model simulates the effect of human optics, cone isomerizations, phototransduction, and mRGC spatial filtering. The model performs a forced choice orientation discrimination task on mRGC responses using a linear support vector machine classifier. The model shows that asymmetries in a decision-maker’s performance across polar angle are greater when assessing the photocurrents than when assessing isomerizations and are greater still when assessing mRGC signals. Nonetheless, the polar angle asymmetries of the mRGC outputs are still considerably smaller than those observed from human performance. We conclude that cone isomerizations, phototransduction and the spatial filtering properties of mRGCs contribute to polar angle performance differences, but that a full account of these differences will entail additional contribution from cortical representations.Keywords:
Eccentricity (behavior)
Spatial frequency
Peripheral vision
Visual phototransduction
Meridian (astronomy)
Peripheral vision
Field of view
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Humans have two distinct vision systems: foveal and peripheral vision. Foveal vision is sharp and detailed, while peripheral vision lacks fidelity. The difference in characteristics of the two systems enable recently popular foveated rendering systems, which seek to increase rendering performance by lowering image quality in the periphery.
Peripheral vision
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Visual processing varies dramatically across the visual field. These differences start in the retina and continue all the way to the visual cortex. Despite these differences in processing, the perceptual experience of humans is remarkably stable and continuous across the visual field. Research in the last decade has shown that processing in peripheral and foveal vision is not independent, but is more directly connected than previously thought. We address three core questions on how peripheral and foveal vision interact, and review recent findings on potentially related phenomena that could provide answers to these questions. First, how is the processing of peripheral and foveal signals related during fixation? Peripheral signals seem to be processed in foveal retinotopic areas to facilitate peripheral object recognition, and foveal information seems to be extrapolated toward the periphery to generate a homogeneous representation of the environment. Second, how are peripheral and foveal signals re-calibrated? Transsaccadic changes in object features lead to a reduction in the discrepancy between peripheral and foveal appearance. Third, how is peripheral and foveal information stitched together across saccades? Peripheral and foveal signals are integrated across saccadic eye movements to average percepts and to reduce uncertainty. Together, these findings illustrate that peripheral and foveal processing are closely connected, mastering the compromise between a large peripheral visual field and high resolution at the fovea.
Peripheral vision
Microsaccade
Fovea centralis
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Visual crowding is the inability to recognize a target object in clutter. Previous studies have shown an increase in crowding in both parafoveal and peripheral vision in normal aging and glaucoma. Here, we ask whether there is any increase in foveal crowding in both normal aging and glaucomatous vision. Twenty-four patients with glaucoma and 24 age-matched normally sighted controls (mean age = 65 ± 7 vs. 60 ± 8 years old) participated in this study. For each subject, we measured the extent of foveal crowding using Pelli's foveal crowding paradigm (2016). We found that the average crowding zone was 0.061 degrees for glaucoma and 0.056 degrees for age-matched normal vision, respectively. These values fall into the range of foveal crowding zones (0.0125 degrees to 0.1 degrees) observed in young normal vision. We, however, did not find any evidence supporting increased foveal crowding in glaucoma (p = 0.375), at least in the early to moderate stages of glaucoma. In the light of previous studies on foveal crowding in normal young vision, we did not find any evidence supporting age-related changes in foveal crowding. Even if there is any, the effect appears to be rather inconsequential. Taken together, our findings suggest unlike parafoveal or peripheral crowding (2 degrees, 4 degrees, 8 degrees, and 10 degrees eccentricities), foveal crowding (<0.25 degrees eccentricity) appears to be less vulnerable to normal aging or moderate glaucomatous damage.
Crowding
Peripheral vision
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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.Rosenholtz, 2016).This would enable peripheral vision 1to process a large area of the visual field very quickly to detect any potentially informative visual items or events.This would then guide consequent eye movements made to project informative parts of the visual scene onto the fovea for further processing.Therefore, examining how visual ensembles are encoded in peripheral vision could increase our understanding of how the visual scene is processed.
Peripheral vision
Visual Search
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It’s well established that vision in the periphery and parafovea is characterized by asymmetries; humans are better at discriminating items along the horizontal meridian compared to the vertical meridian. Similarly, sensitivity in the lower visual field is better than in the upper visual field. Current evidence shows that the extent of these asymmetries decrease with eccentricity, suggesting that they may be absent in the central 1deg fovea. However, due to technical limitations this has never been examined. Thanks to high-precision eyetracking and a gaze contingent display control allowing for more accurate localization of gaze, we probed fine visual discrimination at different isoeccentric locations across the foveola and compared it with corresponding locations in the periphery. Participants (n=10) performed a two-alternative forced-choice discrimination task while maintaining fixation on a central marker. Performance was tested at 8 locations, approximately 20 arcmin from the preferred locus of fixation. The same task was replicated at 4.5 degrees eccentricity (n=7) and the stimuli size was adjusted to account for cortical magnification. Our results show that, similarly to what happens in the visual periphery, humans are more sensitive to stimuli presented along the horizontal than the vertical foveal meridian. While the magnitude of this asymmetry across the meridians is smaller in the fovea than extrafoveally, the magnitude of asymmetry along the vertical meridian is equal. Furthermore, foveal asymmetry on this meridian is flipped compared to what is found extrafoveally: objects in the upper foveal meridian are discerned more easily than those in the lower meridian. These findings show that even foveal vision is characterized by perceptual anisotropies and that their characterization is in part different from what is found in the rest of the visual field. Furthermore, while some asymmetries are larger extrafoveally, others are present to the same extent at both scales.
Meridian (astronomy)
Fovea centralis
Peripheral vision
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Previous foveal/peripheral display systems have typically combined the foveal and peripheral views optically, in a single eye, in order to provide simultaneously both high resolution and wide field of view from a limited number of pixels. While quite effective, this approach can lead to cumbersome optical designs that are not well suited to head-mounted displays. A simpler approach may be possible in the form of a dichoptic vision system, wherein each eye receives a different field of view (FOV) of the same scene, at different resolutions. One eye would be presented with highresolution narrow-FOV foveal imagery, while the other would receive a much wider peripheral FOV. Binocular overlap in the central region would provide some degree of stereoscopic depth perception. It remains to be determined, however, if such a system would be acceptable to users, or if binocular rivalry or other adverse side-effects would degrade visual task performance compared to conventional head-mounted binocular displays. In this paper, we describe a preliminary dichoptic foveal/peripheral vision system and suggest methods by which its usability and performance can be assessed. This effort was funded by the U.S. Air Force Research Laboratory Human Performance Wing under SBIR Topic AF093-018.
Peripheral vision
Binocular rivalry
Field of view
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Flankers can strongly deteriorate performance on a visual target (crowding). For example, vernier offset discrimination strongly deteriorates when neighbouring flankers are presented. Interestingly, performance for longer and shorter flankers is better than performance for flankers of the same length as the vernier. Based on these findings, we proposed that crowding is strongest when the vernier and the flankers group (same length flankers) and weaker when the vernier ungroups from the flankers (shorter or longer flankers). These effects were observed both in foveal and peripheral vision. Here, using high-density EEG, we show that electrophysiological signatures of crowding are also similar in foveal and peripheral vision. In both foveal and peripheral (3.9°) vision, the N1 wave correlated well with performance levels and, hence, with crowding. Amplitudes were highest for the long flankers, intermediate for the short flankers and lowest for the equal length flankers. This effect was observed neither at earlier stages of processing, nor in control conditions matched for stimulus energy. Effects are more pronounced in the fovea than in the periphery. These similarities are evidence for a common mechanism of crowding in both foveal and peripheral vision. Meeting abstract presented at VSS 2013
Peripheral vision
Crowding
Vernier acuity
Stimulus (psychology)
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In both adults and children, peripheral vision is poorer than foveal vision, but there is evidence that detection in peripheral vision is relatively poorer in children than it is in adults. That may contribute to the particularly high pedestrian accident rates of children. Two laboratory experiments investigated peripheral vision in men and women and in boys and girls aged 7, 9 and 11. Using an array of stationary lights, Expt 1 examined reactions to apparent movement (the phi phenomenon) in mid and extreme periphery; and, using film sequences of a moving car, Expt 2 included a comparison of foveal and peripheral fields. Overall there was little evidence to support the hypothesis that children have poorer peripheral vision than adults relative to their foveal vision. Nonetheless there were some experimental differences: in Expt 1, 7-year-olds made fewer detections, particularly in the extreme periphery; and, in both experiments, detections tended to be slower. The relatively complex car movements in Expt 2 were detected faster in foveal than peripheral vision. There were no sex differences. Children detected more movements on the left. In Expt 2 these detections were faster, and children made relatively more simulated road crossings when the car approached from the left (all adults 'crossed' in all trials).
Peripheral vision
Fovea centralis
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Peripheral vision
Eccentricity (behavior)
Fovea centralis
Afterimage
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