1
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Zhu B, Liao M, Liu L. Measuring the impact of suppression on visual acuity in children with amblyopia using a dichoptic visual acuity chart. Front Neurosci 2022; 16:860620. [PMID: 35911993 PMCID: PMC9334724 DOI: 10.3389/fnins.2022.860620] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 06/29/2022] [Indexed: 11/13/2022] Open
Abstract
PurposeTo develop a novel dichoptic visual acuity chart that measures the impact of interocular suppression on the visual acuity of each eye when two eyes are open.MethodsFifty-four subjects (19 anisometropic amblyopia, 20 treated amblyopia, and 15 normal children) participated in this study. The visual acuity that was tested under dichoptic-optotypes condition (i.e., presented optotypes to the untested eye) was compared with that under monocular condition (i.e., cover the untested eye with opaque patch). Visual acuity differences between these two conditions were compared among the three groups. The correlations between visual acuity differences and the depth of interocular suppression were then computed. Some participants performed the visual acuity test under dichoptic-luminance condition (i.e., presented mean luminance to the untested eye), and the test-retest reliability was established.ResultsA reduced visual acuity of the non-dominant eye was found in the dichoptic-optotypes condition for the amblyopia group (P < 0.001) and the treated group (P = 0.001); the difference in the treated group was less than that in the amblyopia group (P < 0.001) but more than that in the normal group (P = 0.026). A significant correlation was found between the visual acuity differences and the depth of suppression, which was tested with a binocular phase combination task (P = 0.005). No change was found in the dichoptic-luminance condition.ConclusionThe amblyopic eye and the previous amblyopic eye seem to suffer from a reduced visual acuity when two eyes are open due to suppression. This was successfully captured by our novel and reliable dichoptic-optotypes visual acuity chart.
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Affiliation(s)
- Bixia Zhu
- Department of Optometry and Visual Science, West China Hospital, Sichuan University, Chengdu, China
| | - Meng Liao
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
| | - Longqian Liu
- Department of Optometry and Visual Science, West China Hospital, Sichuan University, Chengdu, China
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, China
- *Correspondence: Longqian Liu,
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2
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Shamsi F, Liu R, Kwon M. Foveal crowding appears to be robust to normal aging and glaucoma unlike parafoveal and peripheral crowding. J Vis 2022; 22:10. [PMID: 35848904 PMCID: PMC9308014 DOI: 10.1167/jov.22.8.10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
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.
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Affiliation(s)
- Foroogh Shamsi
- Department of Psychology, Northeastern University, Boston, MA, USA.,
| | - Rong Liu
- Department of Psychology, Northeastern University, Boston, MA, USA.,Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.,Department of Life Science and Medicine, University of Science and Technology of China, Hefei, China.,
| | - MiYoung Kwon
- Department of Psychology, Northeastern University, Boston, MA, USA.,Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.,
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3
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Kalpadakis-Smith AV, Tailor VK, Dahlmann-Noor AH, Greenwood JA. Crowding changes appearance systematically in peripheral, amblyopic, and developing vision. J Vis 2022; 22:3. [PMID: 35506917 PMCID: PMC9078053 DOI: 10.1167/jov.22.6.3] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Visual crowding is the disruptive effect of clutter on object recognition. Although most prominent in adult peripheral vision, crowding also disrupts foveal vision in typically developing children and those with strabismic amblyopia. Do these crowding effects share the same mechanism? Here we exploit observations that crowded errors in peripheral vision are not random: Target objects appear either averaged with the flankers (assimilation) or replaced by them (substitution). If amblyopic and developmental crowding share the same mechanism, then their errors should be similarly systematic. We tested foveal vision in children aged 3 to 8 years with typical vision or strabismic amblyopia and peripheral vision in typical adults. The perceptual effects of crowding were measured by requiring observers to adjust a reference stimulus to match the perceived orientation of a target “Vac-Man” element. When the target was surrounded by flankers that differed by ± 30°, all three groups (adults and children with typical or amblyopic vision) reported orientations between the target and flankers (assimilation). Errors were reduced with ± 90° differences but primarily matched the flanker orientation (substitution) when they did occur. A population pooling model of crowding successfully simulated this pattern of errors in all three groups. We conclude that the perceptual effects of amblyopic and developing crowding are systematic and resemble the near periphery in adults, suggesting a common underlying mechanism.
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Affiliation(s)
| | - Vijay K Tailor
- Experimental Psychology, University College London, London, UK.,NIHR Biomedical Research Centre @ Moorfields Eye Hospital, London, UK.,Moorfields Eye Hospital NHS Foundation Trust, London, UK.,
| | - Annegret H Dahlmann-Noor
- NIHR Biomedical Research Centre @ Moorfields Eye Hospital, London, UK.,Moorfields Eye Hospital NHS Foundation Trust, London, UK.,
| | - John A Greenwood
- Experimental Psychology, University College London, London, UK., http://eccentricvision.com
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4
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Rummens K, Sayim B. Multidimensional feature interactions in visual crowding: When configural cues eliminate the polarity advantage. J Vis 2022; 22:2. [PMID: 35503508 PMCID: PMC9078080 DOI: 10.1167/jov.22.6.2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 03/21/2022] [Indexed: 11/24/2022] Open
Abstract
Crowding occurs when surrounding objects (flankers) impair target perception. A key property of crowding is the weaker interference when target and flankers strongly differ on a given dimension. For instance, identification of a target letter is usually superior with flankers of opposite versus the same contrast polarity as the target (the "polarity advantage"). High performance when target-flanker similarity is low has been attributed to the ungrouping of target and flankers. Here, we show that configural cues can override the usual advantage of low target-flanker similarity, and strong target-flanker grouping can reduce - instead of exacerbate - crowding. In Experiment 1, observers were presented with line triplets in the periphery and reported the tilt (left or right) of the central line. Target and flankers had the same (uniform condition) or opposite contrast polarity (alternating condition). Flanker configurations were either upright (||), unidirectionally tilted (\\ or //), or bidirectionally tilted (\/ or /\). Upright flankers yielded stronger crowding than unidirectional flankers, and weaker crowding than bidirectional flankers. Importantly, our results revealed a clear interaction between contrast polarity and flanker configuration. Triplets with upright and bidirectional flankers, but not unidirectional flankers, showed the polarity advantage. In Experiments 2 and 3, we showed that emergent features and redundancy masking (i.e. the reduction of the number of perceived items in repeating configurations) made it easier to discriminate between uniform triplets when flanker tilts were unidirectional (but not when bidirectional). We propose that the spatial configurations of uniform triplets with unidirectional flankers provided sufficient task-relevant information to enable a similar performance as with alternating triplets: strong-target flanker grouping alleviated crowding. We suggest that features which modulate crowding strength can interact non-additively, limiting the validity of typical crowding rules to contexts where only single, independent dimensions determine the effects of target-flanker similarity.
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Affiliation(s)
- Koen Rummens
- University of Bern, Institute of Psychology, Bern, Switzerland
| | - Bilge Sayim
- University of Bern, Institute of Psychology, Bern, Switzerland
- Université de Lille, CNRS, UMR 9193 - SCALab - Sciences Cognitives et Sciences Affectives, Lille, France
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5
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Hussain Z, McGraw PV. Disruption of Positional Encoding at Small Separations in the Amblyopic Periphery. Invest Ophthalmol Vis Sci 2022; 63:15. [PMID: 35446345 PMCID: PMC9034712 DOI: 10.1167/iovs.63.4.15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Positional judgments in amblyopia are impaired more at the center of the visual field than in the periphery. However, the effects of visual field position frequently are confounded with stimulus separation. The purpose of this experiment was to parse the effects of stimulus separation and eccentricity on the positional deficit in amblyopia. Methods Subjects adjusted the positions of stimuli of varying separations on isoeccentric arcs. The task was simultaneous bisection and alignment of broadband, high-contrast, uncrowded targets with reference to central fixation. Ten strabismic amblyopes and five normally sighted controls performed the task dichoptically; a subset of amblyopes performed the task monocularly with the amblyopic eye. Spread (inverse of precision) and bias were measured at multiple visual field locations comprising two to three separation × four eccentricity conditions in each visual field quadrant. Results In normal controls, both spread and bias increased with eccentricity, and spread (but not bias) increased linearly with separation until 7° eccentricity. Strabismic amblyopes showed a different profile: spread and bias were higher at small separations at all eccentricities, such that performance showed a quadratic trend against separation. Thus, at each eccentricity, the difference in performance between groups was largest at the smallest separation. Conclusions These results are consistent with disruptions in Weber mechanisms of positional encoding in strabismic amblyopia, and indicate that binocular stimulation by proximal targets produces a loss of spatial precision well beyond the fovea.
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Affiliation(s)
- Zahra Hussain
- Department of Psychology, American University of Beirut, Lebanon
| | - Paul V McGraw
- School of Psychology, University of Nottingham, United Kingdom
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6
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Exogenous attention generalizes location transfer of perceptual learning in adults with amblyopia. iScience 2022; 25:103839. [PMID: 35243224 PMCID: PMC8857599 DOI: 10.1016/j.isci.2022.103839] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 09/19/2021] [Accepted: 01/25/2022] [Indexed: 12/04/2022] Open
Abstract
Visual perceptual learning (VPL) is a behavioral manifestation of brain neuroplasticity. However, its practical effectiveness is limited because improvements are often specific to the trained conditions and require significant time and effort. It is critical to understand the conditions that promote learning and transfer. Covert endogenous (voluntary) and exogenous (involuntary) spatial attention help overcome VPL location specificity in neurotypical adults, but whether they also do so for people with atypical visual development is unknown. This study investigates the role of exogenous attention during VPL in adults with amblyopia, an ideal population given their asymmetrically developed, but highly plastic, visual cortex. Here we show that training on a discrimination task leads to improvements in foveal contrast sensitivity, acuity, and stereoacuity. Notably, exogenous attention helps generalize learning beyond trained spatial locations. Future large-scale studies can verify the extent to which attention enhances the effectiveness of perceptual learning during rehabilitation of visual disorders. Contrast sensitivity (CS)-based VPL in amblyopes improves CS, acuity and stereoacuity Similar improvement in trained amblyopic eye and untrained fellow eye Exogenous spatial attention facilitates location transfer of VPL in amblyopic adults
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7
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Xi H, Wu R, Wang B, Chen L. Topological difference between target and flankers alleviates crowding effect. J Vis 2020; 20:9. [PMID: 32926072 PMCID: PMC7509911 DOI: 10.1167/jov.20.9.9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In the crowding effect, object recognition in the periphery deteriorates when other items flank the target, especially if they share similarities. Here, we report that the similarity defined by topological property (differences in number of holes) influences the crowding effect. Orientation discrimination tasks suggested that the crowding effect was weaker with a topological different (TD) flanker than a topological equivalent (TE) flanker and an existing inward-outward anisotropy phenomenon. In another experiment, both an outer and an inner flanker were used to constitute four different conditions. The performance of an outer TD flanker and an inner TE flanker was superior to that of an outer TE flanker and an inner TD flanker, even though the items of the stimuli were the same. Different stimuli were used to control for local features. To eliminate the possible explanation of confusability, we selected pairs of letters with matched confusability, but one pair was TD and another was TE. The letter identification performance was better for the TD condition. Lastly, we investigated the digit identification under four conditions with varied spacing. Regardless of different spacing, the crowding effect was reduced by a topological different flanker. The results collectively suggest that topological property plays a role in the perceptual grouping, which modulates the crowding effect.
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Affiliation(s)
- Huanjun Xi
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Ruijie Wu
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Bo Wang
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Lin Chen
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China.,CAS Center for Excellence in Brain Science and Intelligence Technology, Shanghai, China
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8
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Strasburger H. Seven Myths on Crowding and Peripheral Vision. Iperception 2020; 11:2041669520913052. [PMID: 32489576 PMCID: PMC7238452 DOI: 10.1177/2041669520913052] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 02/13/2020] [Indexed: 12/03/2022] Open
Abstract
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.
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Affiliation(s)
- Hans Strasburger
- Georg-August-Universität, Göttingen, Germany
Ludwig-Maximilians-Universität, München, Germany
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9
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Richards MD, Goltz HC, Wong AM. Audiovisual perception in amblyopia: A review and synthesis. Exp Eye Res 2019; 183:68-75. [DOI: 10.1016/j.exer.2018.04.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 04/27/2018] [Accepted: 04/28/2018] [Indexed: 11/15/2022]
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10
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Chow A, Giaschi D, Thompson B. Dichoptic Attentive Motion Tracking is Biased Toward the Nonamblyopic Eye in Strabismic Amblyopia. ACTA ACUST UNITED AC 2018; 59:4572-4580. [DOI: 10.1167/iovs.18-25236] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Amy Chow
- Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
| | - Deborah Giaschi
- Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Benjamin Thompson
- Optometry and Vision Science, University of Waterloo, Waterloo, Ontario, Canada
- Optometry and Vision Science, University of Auckland, Auckland, New Zealand
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11
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Kalpadakis-Smith AV, Goffaux V, Greenwood JA. Crowding for faces is determined by visual (not holistic) similarity: Evidence from judgements of eye position. Sci Rep 2018; 8:12556. [PMID: 30135454 PMCID: PMC6105622 DOI: 10.1038/s41598-018-30900-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 08/01/2018] [Indexed: 11/08/2022] Open
Abstract
Crowding (the disruption of object recognition in clutter) presents the fundamental limitation on peripheral vision. For simple objects, crowding is strong when target/flanker elements are similar and weak when they differ - a selectivity for target-flanker similarity. In contrast, the identification of upright holistically-processed face stimuli is more strongly impaired by upright than inverted flankers, whereas inverted face-targets are impaired by both - a pattern attributed to an additional stage of crowding selective for "holistic similarity" between faces. We propose instead that crowding is selective for target-flanker similarity in all stimuli, but that this selectivity is obscured by task difficulty with inverted face-targets. Using judgements of horizontal eye-position that are minimally affected by inversion, we find that crowding is strong when target-flanker orientations match and weak when they differ for both upright and inverted face-targets. By increasing task difficulty, we show that this selectivity for target-flanker similarity is obscured even for upright face-targets. We further demonstrate that this selectivity follows differences in the spatial order of facial features, rather than "holistic similarity" per se. There is consequently no need to invoke a distinct stage of holistic crowding for faces - crowding is selective for target-flanker similarity, even with complex stimuli such as faces.
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Affiliation(s)
| | - Valérie Goffaux
- Research Institute for Psychological Science, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
- Institute of Neuroscience, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
- Department of Cognitive Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - John A Greenwood
- Experimental Psychology, University College London, London, United Kingdom
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12
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Musilová L, Pluhácek F, Marten-Ellis SM, Bedell HE, Siderov J. Contour interaction under photopic and scotopic conditions. J Vis 2018; 18:5. [PMID: 30029215 PMCID: PMC6005630 DOI: 10.1167/18.6.5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In the present study, we asked whether contour interaction undergoes significant changes for different luminance levels in the central and peripheral visual field. This study included nine normal observers at two laboratories (five at Palacky University Olomouc, Czech Republic and four at the University of Houston, USA). Observers viewed a randomly selected Sloan letter surrounded by four equally spaced bars for several separations measured edge-to-edge in min arc. Stimuli were viewed foveally under photopic and mesopic luminances and between 5° and 12° peripherally for four different background luminances of the display monitors, corresponding to photopic, mesopic, scotopic, and dim scotopic levels. The extent of the contour interaction in the fovea is approximately 20 times smaller than in the periphery. Whereas the magnitude of foveal contour interaction markedly decreases with decreasing luminance, no consistent luminance-induced change occurs in peripheral contour interaction. The extent of contour interaction does not scale with the size of the target letter, either in the fovea or peripherally. The results support a neural origin of contour interaction consistent with the properties of center-surround antagonism.
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Affiliation(s)
- Lenka Musilová
- Palacky University Olomouc, Department of Optics, Olomouc, Czech Republic
| | - František Pluhácek
- Palacky University Olomouc, Department of Optics, Olomouc, Czech Republic
| | | | - Harold E Bedell
- University of Houston, College of Optometry, Houston, Texas, USA
| | - John Siderov
- Anglia Ruskin University, Department of Vision & Hearing Sciences, Cambridge, UK
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13
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Perceptual averaging of facial expressions requires visual awareness and attention. Conscious Cogn 2018; 62:110-126. [PMID: 29573970 DOI: 10.1016/j.concog.2018.03.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Revised: 12/27/2017] [Accepted: 03/13/2018] [Indexed: 11/23/2022]
Abstract
Humans, as highly social animals, are regularly exposed to the faces of conspecifics-often more than one at a time. This feature of social living is important for understanding face perception, not just because it means that information from faces is available in bulk, but also because it changes the way individuals are perceived. For instance, when two faces are seen nearby one another, they tend to look like each other. This phenomenon of perceptual averaging is robust when both faces are seen and attended. But in everyday life, some faces may not receive the full benefit of attention, or they may not be visible at all. We evaluated whether perceptual averaging of relatively complex and simple information on faces, including facial expression and head orientation, can still occur even in these circumstances. In particular, we used object-substitution masking (OSM) and a dual-task designed to disrupt visual awareness and attention, respectively, during evaluations of briefly presented face pairs. Disruptions of awareness or attention eliminated averaging of facial expression, whereas orientation averaging persisted in spite of these challenges. These results demonstrate boundary conditions for the process of perceptual averaging. More generally, they provide insight into how the visual system processes multitudes of objects, both simple and complex, both with and without attention and awareness.
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14
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Ghahghaei S, Walker L. The crowding factor method applied to parafoveal vision. J Vis 2016; 16:30. [PMID: 27690170 PMCID: PMC5054730 DOI: 10.1167/16.11.30] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 08/16/2016] [Indexed: 11/30/2022] Open
Abstract
Crowding increases with eccentricity and is most readily observed in the periphery. During natural, active vision, however, central vision plays an important role. Measures of critical distance to estimate crowding are difficult in central vision, as these distances are small. Any overlap of flankers with the target may create an overlay masking confound. The crowding factor method avoids this issue by simultaneously modulating target size and flanker distance and using a ratio to compare crowded to uncrowded conditions. This method was developed and applied in the periphery (Petrov & Meleshkevich, 2011b). In this work, we apply the method to characterize crowding in parafoveal vision (<3.5 visual degrees) with spatial uncertainty. We find that eccentricity and hemifield have less impact on crowding than in the periphery, yet radial/tangential asymmetries are clearly preserved. There are considerable idiosyncratic differences observed between participants. The crowding factor method provides a powerful tool for examining crowding in central and peripheral vision, which will be useful in future studies that seek to understand visual processing under natural, active viewing conditions.
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Affiliation(s)
- Saeideh Ghahghaei
- The Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA. . http://www.ski.org/users/saeideh-ghahghaei
| | - Laura Walker
- The Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA
- Envision Research Institute, Wichita, KS, USA. . http://research.envisionus.com/Team/Laura-Walker
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15
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Song S, Levi DM, Pelli DG. A double dissociation of the acuity and crowding limits to letter identification, and the promise of improved visual screening. J Vis 2014; 14:3. [PMID: 24799622 PMCID: PMC4021854 DOI: 10.1167/14.5.3] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2013] [Accepted: 02/14/2014] [Indexed: 11/24/2022] Open
Abstract
Here, we systematically explore the size and spacing requirements for identifying a letter among other letters. We measure acuity for flanked and unflanked letters, centrally and peripherally, in normals and amblyopes. We find that acuity, overlap masking, and crowding each demand a minimum size or spacing for readable text. Just measuring flanked and unflanked acuity is enough for our proposed model to predict the observer's threshold size and spacing for letters at any eccentricity. We also find that amblyopia in adults retains the character of the childhood condition that caused it. Amblyopia is a developmental neural deficit that can occur as a result of either strabismus or anisometropia in childhood. Peripheral viewing during childhood due to strabismus results in amblyopia that is crowding limited, like peripheral vision. Optical blur of one eye during childhood due to anisometropia without strabismus results in amblyopia that is acuity limited, like blurred vision. Furthermore, we find that the spacing:acuity ratio of flanked and unflanked acuity can distinguish strabismic amblyopia from purely anisometropic amblyopia in nearly perfect agreement with lack of stereopsis. A scatter diagram of threshold spacing versus acuity, one point per patient, for several diagnostic groups, reveals the diagnostic power of flanked acuity testing. These results and two demonstrations indicate that the sensitivity of visual screening tests can be improved by using flankers that are more tightly spaced and letter like. Finally, in concert with Strappini, Pelli, Di Pace, and Martelli (submitted), we jointly report a double dissociation between acuity and crowding. Two clinical conditions-anisometropic amblyopia and apperceptive agnosia-each selectively impair either acuity A or the spacing:acuity ratio S/A, not both. Furthermore, when we specifically estimate crowding, we find a double dissociation between acuity and crowding. Models of human object recognition will need to accommodate this newly discovered independence of acuity and crowding.
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Affiliation(s)
- Shuang Song
- Vision Science, School of Optometry, UC Berkeley, Berkeley, CA, USA
| | - Dennis M. Levi
- School of Optometry and Helen Wills Neuroscience, Institute, UC Berkeley, Berkeley, CA, USA
| | - Denis G. Pelli
- Psychology & Neural Science, New York University, New York, NY, USA
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16
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Siderov J, Waugh SJ, Bedell HE. Foveal contour interaction on the edge: Response to ‘Letter-to-the-Editor’ by Drs. Coates and Levi. Vision Res 2014; 96:145-8. [DOI: 10.1016/j.visres.2013.12.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Revised: 12/16/2013] [Accepted: 12/19/2013] [Indexed: 10/25/2022]
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17
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Abstract
Over the last 35 years or so, there has been substantial progress in revealing and characterizing the many interesting and sometimes mysterious sensory abnormalities that accompany amblyopia. A goal of many of the studies has been to try to make the link between the sensory losses and the underlying neural losses, resulting in several hypotheses about the site, nature, and cause of amblyopia. This article reviews some of these hypotheses, and the assumptions that link the sensory losses to specific physiological alterations in the brain. Despite intensive study, it turns out to be quite difficult to make a simple linking hypothesis, at least at the level of single neurons, and the locus of the sensory loss remains elusive. It is now clear that the simplest notion-that reduced contrast sensitivity of neurons in cortical area V1 explains the reduction in contrast sensitivity-is too simplistic. Considerations of noise, noise correlations, pooling, and the weighting of information also play a critically important role in making perceptual decisions, and our current models of amblyopia do not adequately take these into account. Indeed, although the reduction of contrast sensitivity is generally considered to reflect "early" neural changes, it seems plausible that it reflects changes at many stages of visual processing.
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Affiliation(s)
- Dennis M Levi
- School of Optometry & Helen Wills Neuroscience Institute, University of California, Berkeley, California
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Sayim B, Cavanagh P. Grouping and crowding affect target appearance over different spatial scales. PLoS One 2013; 8:e71188. [PMID: 23967164 PMCID: PMC3742795 DOI: 10.1371/journal.pone.0071188] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 06/26/2013] [Indexed: 11/21/2022] Open
Abstract
Crowding is the impairment of peripheral target perception by nearby flankers. A number of recent studies have shown that crowding shares many features with grouping. Here, we investigate whether effects of crowding and grouping on target perception are related by asking whether they operate over the same spatial scale. A target letter T had two sets of flanking Ts of varying orientations. The first set was presented close to the target, yielding strong crowding. The second set was either close enough to cause crowding on their own or too far to cause crowding on their own. The Ts of the second set had the same orientation that either matched the target's orientation (Grouped condition) or not (Ungrouped condition). In Experiment 1, the Grouped flankers reduced crowding independently of their distance from the target, suggesting that grouping operated over larger distances than crowding. In Experiments 2 and 3 we found that grouping did not affect sensitivity but produced a strong bias to report that the grouped orientation was present at the target location whether or not it was. Finally, we investigated whether this bias was a response or perceptual bias, rejecting the former in favor of a perceptual grouping explanation. We suggest that the effect of grouping is to assimilate the target to the identity of surrounding flankers when they are all the same, and that this shape assimilation effect differs in its spatial scale from the integration effect of crowding.
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Affiliation(s)
- Bilge Sayim
- Laboratoire Psychologie de la Perception, Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
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19
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Contour interaction for foveal acuity targets at different luminances. Vision Res 2013; 89:90-5. [DOI: 10.1016/j.visres.2013.07.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Revised: 06/26/2013] [Accepted: 07/12/2013] [Indexed: 11/17/2022]
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Abstract
PURPOSE Acuity measurement is a fundamental method to assess visual performance in the clinic. Little is known about how acuity measured in the presence of neighboring letters, as in the case of letter charts, changes with contrast and with nonfoveal viewing. This information is crucial for acuity measurement using low-contrast charts and when patients cannot use their fovea. In this study, we evaluated how optotype acuity, with and without flankers, is affected by contrast and eccentricity. METHODS Five young adults with normal vision identified the orientation of a Tumbling-E presented alone or in the presence of four flanking Tumbling-Es. Edge-to-edge letter spacing ranged from 1 to 20 bar widths. Stimuli were presented on a white background for 150 ms with Weber contrast ranging from -2.5% to -99%. Flankers had the same size and contrast as the target. Testings were performed at the fovea, 3°, 5°, and 10° in the inferior visual field. RESULTS When plotted as a function of letter spacing, acuity remains unaffected by the presence of flankers until the flankers are within the critical spacing, which averages an edge-to-edge spacing of 4.4 bar widths at the fovea and approximately 16 bar widths at all three eccentricities. Critical spacing decreases with a reduction in contrast. When plotted as a function of contrast, acuity only worsens when the contrast falls below approximately 24% at the fovea and 17% in the periphery, for flanked and unflanked conditions alike. CONCLUSIONS The letter spacing on conventional letter charts exceeds the critical spacing for acuity measurement at the fovea, at all contrast levels. Thus, these charts are appropriate for assessing foveal acuity. In the periphery, the critical spacing is larger than the letter spacing on conventional charts. Consequently, these charts may underestimate the acuity measured in the periphery because of the effects of crowding.
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Affiliation(s)
- Daniel R Coates
- Vision Science Graduate Program, and School of Optometry, University of California-Berkeley, CA 94720, USA.
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21
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Foveal visual acuity is worse and shows stronger contour interaction effects for contrast-modulated than luminance-modulated Cs. Vis Neurosci 2013; 30:105-20. [PMID: 23731769 DOI: 10.1017/s0952523813000102] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Contrast-modulated (CM) stimuli are processed by spatial mechanisms that operate at larger spatial scales than those processing luminance-modulated (LM) stimuli and may be more prone to deficits in developing, amblyopic, and aging visual systems. Understanding neural mechanisms of contour interaction or crowding will help in detecting disorders of spatial vision. In this study, contour interaction effects on visual acuity for LM and CM C and bar stimuli are assessed in normal foveal vision. In Experiment 1, visual acuity is measured for all-LM and all-CM stimuli, at ~3.5× above their respective modulation thresholds. In Experiment 2, visual acuity is measured for Cs and bars of different type (LM C with CM bars and vice versa). Visual acuity is degraded for CM compared with LM Cs (0.46 ± 0.04 logMAR vs. 0.18 ± 0.04 logMAR). With nearby bars, CM acuity is degraded further (0.23 ± 0.01 logMAR or ~2 lines on an acuity chart), significantly more than LM acuity (0.11 ± 0.01 logMAR, ~1 line). Contour interaction for CM stimuli extends over greater distances (arcmin) than it does for LM stimuli, but extents are similar with respect to acuities (~3.5× the C gap width). Contour interaction is evident when the Cs and bars are defined differently: it is stronger when an LM C is flanked by CM bars (0.17 ± 0.03 logMAR) than when a CM C is flanked by LM bars (0.08 ± 0.02 logMAR). Our results suggest that contour interaction for foveally viewed acuity stimuli involves feature integration, such that the outputs of receptive fields representing Cs and bars are combined. Contour interaction operates at LM and CM representational stages, it can occur across stage, and it is enhanced at the CM stage. Greater contour interaction for CM Cs and bars could hold value for visual acuity testing and earlier diagnosis of conditions for which crowding is important, such as in amblyopia.
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Wallace JM, Chiu MK, Nandy AS, Tjan BS. Crowding during restricted and free viewing. Vision Res 2013; 84:50-9. [PMID: 23563172 DOI: 10.1016/j.visres.2013.03.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2012] [Revised: 03/05/2013] [Accepted: 03/25/2013] [Indexed: 11/28/2022]
Abstract
Crowding impairs the perception of form in peripheral vision. It is likely to be a key limiting factor of form vision in patients without central vision. Crowding has been extensively studied in normally sighted individuals, typically with a stimulus duration of a few hundred milliseconds to avoid eye movements. These restricted testing conditions do not reflect the natural behavior of a patient with central field loss. Could unlimited stimulus duration and unrestricted eye movements change the properties of crowding in any fundamental way? We studied letter identification in the peripheral vision of normally sighted observers in three conditions: (i) a fixation condition with a brief stimulus presentation of 250 ms, (ii) another fixation condition but with an unlimited viewing time, and (iii) an unrestricted eye movement condition with an artificial central scotoma and an unlimited viewing time. In all conditions, contrast thresholds were measured as a function of target-to-flanker spacing, from which we estimated the spatial extent of crowding in terms of critical spacing. We found that presentation duration beyond 250 ms had little effect on critical spacing with stable gaze. With unrestricted eye movements and a simulated central scotoma, we found a large variability in critical spacing across observers, but more importantly, the variability in critical spacing was well correlated with the variability in target eccentricity. Our results assure that the large body of findings on crowding made with briefly presented stimuli remains relevant to conditions where viewing time is unconstrained. Our results further suggest that impaired oculomotor control associated with central vision loss can confound peripheral form vision beyond the limits imposed by crowding.
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Affiliation(s)
- Julian M Wallace
- Department of Psychology, University of Southern California, USA
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23
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Abstract
Both crowding and binocular rivalry impair object perception, but their influence on object perception has so far only been investigated in separate fields. Three experiments investigated the joint influences of crowding and rivalry on object perception (orientation discrimination). Experiment 1 investigated how crowding and rivalry influence orientation discrimination together. Experiment 2 tested whether rivalry between flankers affects crowding using an orientation discrimination task. Experiment 3 tested whether crowding affects the temporal dynamics of the rivalry between a target and a rival stimulus. In Experiment 1, judgments of target orientation were more impaired when crowding and rivalry were simultaneously induced than when they were separately induced and their effects were combined. In Experiment 2, judgments of target orientation were impaired even when flankers were undergoing rivalry, thus highlighting the importance of the presence of flankers. Experiment 3 showed that flankers presented in the neighborhood of a target undergoing rivalry shortened target dominance and prolonged target suppression. The augmented impairments of object perception found in Experiments 1 and 3 suggest that crowding and rivalry interact, presumably through signal suppression. The adverse effect of flankers shown in Experiment 2 suggests that inappropriate feature integration may have additionally contributed to this interaction.
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Affiliation(s)
- Sangrae Kim
- Graduate Program in Cognitive Science, Yonsei University, Seoul, Republic of Korea
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Pardhan S, Gonzalez-Alvarez C, Subramanian A, Chung STL. How do flanking objects affect reaching and grasping behavior in participants with macular disorders? Invest Ophthalmol Vis Sci 2012; 53:6687-94. [PMID: 22918639 PMCID: PMC4608677 DOI: 10.1167/iovs.12-9821] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 05/31/2012] [Accepted: 08/20/2012] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate how objects (flankers) placed on either side of a target affect reaching and grasping behavior in visually impaired (VI) subjects due to macular disorders compared with age-matched normals. METHODS Subjects reached out to grasp a cylindrical target placed on its own and when it had two identical objects (flankers) placed either half or one target diameter away on each side of the target. A motion analysis system (Vicon 460) recorded and reconstructed the 3-dimemsional (3D) hand and finger movements. Kinematic data for transport and grasping mechanisms were measured. RESULTS In subjects with VI, crowding effected the overall movement duration, time after maximum velocity, and maximum grip aperture. Maximum effect was shown when the flankers were placed close to the target (high-level crowding) with a decreased effect shown for flankers placed farther away (medium-level crowding). Compared with normals, subjects with VI generally took longer to initiate the hand movement and to complete the movement. Time after maximum velocity and time after maximum grip aperture were also longer in subjects with VI. No interaction effects were found for any of the indices for the different levels of crowding in the two visual groups. CONCLUSIONS Reaching and grasping behavior is compromised in subjects with VI due to macular disorders compared with normals, and crowding affected performance for both normal subjects and those with VI. Flankers placed half an object diameter away showed greater deterioration than those placed further away.
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Affiliation(s)
- Shahina Pardhan
- Vision and Eye Research Unit, Postgraduate Medical Institute, Anglia Ruskin University, Cambridge, United Kingdom.
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26
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Huurneman B, Boonstra FN, Cox RFA, Cillessen AHN, van Rens G. A systematic review on 'Foveal Crowding' in visually impaired children and perceptual learning as a method to reduce Crowding. BMC Ophthalmol 2012; 12:27. [PMID: 22824242 PMCID: PMC3416571 DOI: 10.1186/1471-2415-12-27] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2011] [Accepted: 07/23/2012] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND This systematic review gives an overview of foveal crowding (the inability to recognize objects due to surrounding nearby contours in foveal vision) and possible interventions. Foveal crowding can have a major effect on reading rate and deciphering small pieces of information from busy visual scenes. Three specific groups experience more foveal crowding than adults with normal vision (NV): 1) children with NV, 2) visually impaired (VI) children and adults and 3) children with cerebral visual impairment (CVI). The extent and magnitude of foveal crowding as well as interventions aimed at reducing crowding were investigated in this review. The twofold goal of this review is : [A] to compare foveal crowding in children with NV, VI children and adults and CVI children and [B] to compare interventions to reduce crowding. METHODS Three electronic databases were used to conduct the literature search: PubMed, PsycINFO (Ovid), and Cochrane. Additional studies were identified by contacting experts. Search terms included visual perception, contour interaction, crowding, crowded, and contour interactions. RESULTS Children with normal vision show an extent of contour interaction over an area 1.5-3× as large as that seen in adults NV. The magnitude of contour interaction normally ranges between 1-2 lines on an acuity chart and this magnitude is even larger when stimuli are arranged in a circular configuration. Adults with congenital nystagmus (CN) show interaction areas that are 2× larger than those seen adults with NV. The magnitude of the crowding effect is also 2× as large in individuals with CN as in individuals with NV. Finally, children with CVI experience a magnitude of the crowding effect that is 3× the size of that experienced by adults with NV. CONCLUSIONS The methodological heterogeneity, the diversity in paradigms used to measure crowding, made it impossible to conduct a meta-analysis. This is the first systematic review to compare crowding ratios and it shows that charts with 50% interoptotype spacing were most sensitive to capture crowding effects. The groups that showed the largest crowding effects were individuals with CN, VI adults with central scotomas and children with CVI. Perceptual Learning seems to be a promising technique to reduce excessive foveal crowding effects.
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Affiliation(s)
- Bianca Huurneman
- Bartiméus, Institute for the Visually Impaired, Zeist, the Netherlands
- Behavioural Science Institute, Radboud University Nijmegen, Nijmegen, the Netherlands
| | - F Nienke Boonstra
- Bartiméus, Institute for the Visually Impaired, Zeist, the Netherlands
| | - Ralf FA Cox
- Bartiméus, Institute for the Visually Impaired, Zeist, the Netherlands
- Department of Developmental Psychology, University of Groningen, Groningen, The Netherlands
| | - Antonius HN Cillessen
- Behavioural Science Institute, Radboud University Nijmegen, Nijmegen, the Netherlands
| | - Ger van Rens
- Free University Medical Centre, Free University, Amsterdam, the Netherlands
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Chung STL, Li RW, Levi DM. Learning to identify near-acuity letters, either with or without flankers, results in improved letter size and spacing limits in adults with amblyopia. PLoS One 2012; 7:e35829. [PMID: 22558234 PMCID: PMC3340394 DOI: 10.1371/journal.pone.0035829] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2011] [Accepted: 03/26/2012] [Indexed: 11/18/2022] Open
Abstract
Amblyopia is a developmental abnormality that results in deficits for a wide range of visual tasks, most notably, the reduced ability to see fine details, the loss in contrast sensitivity especially for small objects and the difficulty in seeing objects in clutter (crowding). The primary goal of this study was to evaluate whether crowding can be ameliorated in adults with amblyopia through perceptual learning using a flanked letter identification task that was designed to reduce crowding, and if so, whether the improvements transfer to untrained visual functions: visual acuity, contrast sensitivity and the size of visual span (the amount of information obtained in one fixation). To evaluate whether the improvements following this training task were specific to training with flankers, we also trained another group of adult observers with amblyopia using a single letter identification task that was designed to improve letter contrast sensitivity, not crowding. Following 10,000 trials of training, both groups of observers showed improvements in the respective training task. The improvements generalized to improved visual acuity, letter contrast sensitivity, size of the visual span, and reduced crowding. The magnitude of the improvement for each of these measurements was similar in the two training groups. Perceptual learning regimens aimed at reducing crowding or improving letter contrast sensitivity are both effective in improving visual acuity, contrast sensitivity for near-acuity objects and reducing the crowding effect, and could be useful as a clinical treatment for amblyopia.
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Affiliation(s)
- Susana T L Chung
- School of Optometry, University of California, Berkeley, California, United States of America.
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28
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Abstract
Amblyopia is a developmental visual disorder of cortical origin, characterized by crowding and poor acuity in central vision of the affected eye. Crowding refers to the adverse effects of surrounding items on object identification, common only in normal peripheral but not central vision. We trained a group of adult human amblyopes on a crowded letter identification task to assess whether the crowding problem can be ameliorated. Letter size was fixed well above the acuity limit, and letter spacing was varied to obtain spacing thresholds for central target identification. Normally sighted observers practiced the same task in their lower peripheral visual field. Independent measures of acuity were taken in flanked and unflanked conditions before and after training to measure crowding ratios at three fixed letter separations. Practice improved the letter spacing thresholds of both groups on the training task, and crowding ratios were reduced after posttest. The reductions in crowding in amblyopes were associated with improvements in standard measures of visual acuity. Thus, perceptual learning reduced the deleterious effects of crowding in amblyopia and in the normal periphery. The results support the effectiveness of plasticity-based approaches for improving vision in adult amblyopes and suggest experience-dependent effects on the cortical substrates of crowding.
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Yeotikar NS, Khuu SK, Asper LJ, Suttle CM. Configuration specificity of crowding in peripheral vision. Vision Res 2011; 51:1239-48. [DOI: 10.1016/j.visres.2011.03.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Revised: 02/08/2011] [Accepted: 03/24/2011] [Indexed: 11/30/2022]
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Whitney D, Levi DM. Visual crowding: a fundamental limit on conscious perception and object recognition. Trends Cogn Sci 2011; 15:160-8. [PMID: 21420894 DOI: 10.1016/j.tics.2011.02.005] [Citation(s) in RCA: 466] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Revised: 02/14/2011] [Accepted: 02/14/2011] [Indexed: 11/19/2022]
Abstract
Crowding, the inability to recognize objects in clutter, sets a fundamental limit on conscious visual perception and object recognition throughout most of the visual field. Despite how widespread and essential it is to object recognition, reading and visually guided action, a solid operational definition of what crowding is has only recently become clear. The goal of this review is to provide a broad-based synthesis of the most recent findings in this area, to define what crowding is and is not, and to set the stage for future work that will extend our understanding of crowding well beyond low-level vision. Here we define six diagnostic criteria for what counts as crowding, and further describe factors that both escape and break crowding. All of these lead to the conclusion that crowding occurs at multiple stages in the visual hierarchy.
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Affiliation(s)
- David Whitney
- Department of Psychology, University of California, Berkeley, CA 94720-1650, USA
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31
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Developmental changes during childhood in single-letter acuity and its crowding by surrounding contours. J Exp Child Psychol 2010; 107:423-37. [PMID: 20633893 DOI: 10.1016/j.jecp.2010.05.009] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Revised: 05/25/2010] [Accepted: 05/25/2010] [Indexed: 11/23/2022]
Abstract
Crowding refers to impaired target recognition caused by surrounding contours. We investigated the development of crowding in central vision by comparing single-letter and crowding thresholds in groups of 5-year-olds, 8-year-olds, 11-year-olds, and adults. The task was to discriminate the orientation of a Sloan letter E. Single-letter thresholds, defined as the stroke width forming the smallest discriminable E, were worse than those of adults (0.83 arcmin) at 5 years of age (1.05 arcmin) but not at older ages (8-year-olds: 0.81 arcmin; 11-year-olds: 0.78 arcmin). The maximum distances over which crowding occurred, as measured in multiples of threshold stroke width, were smaller in adults (2.83) than in the three groups of children, who did not differ from each other (5-year-olds: 7.03; 8-year-olds: 7.84; 11-year-olds: 7.13). Thus, even 11-year-olds are more affected than adults by surrounding contours despite having single-letter acuity that has been mature for several years. The stronger influence of crowding in children may be caused by immaturities in the brain areas beyond the primary visual cortex (V1) where early visual inputs are combined and may contribute to their slower reading speed.
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Abstract
Within the last five years, there have been a number of exciting new advances in our knowledge and understanding of amblyopia. This article reviews recent psychophysical studies of naturally occurring amblyopia in humans. These studies suggest that: 1) There are significant differences in the patterns of visual loss among the clinically defined categories of amblyopes. A key factor in determining the nature of the loss is the presence or absence of binocularity. 2) Dysfunction within the amblyopic visual system first occurs in area V1, and the effects of amblyopia may be amplified downstream. 3) There appears to be substantial neural plasticity in the amblyopic brain beyond the "critical period."
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Affiliation(s)
- Dennis M Levi
- University of California at Berkeley, School of Optometry, Berkeley, CA 94720, USA.
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Polat U. Making perceptual learning practical to improve visual functions. Vision Res 2009; 49:2566-73. [PMID: 19520103 DOI: 10.1016/j.visres.2009.06.005] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2008] [Revised: 06/02/2009] [Accepted: 06/04/2009] [Indexed: 10/20/2022]
Abstract
Task-specific improvement in performance after training is well established. The finding that learning is stimulus-specific and does not transfer well between different stimuli, between stimulus locations in the visual field, or between the two eyes has been used to support the notion that neurons or assemblies of neurons are modified at the earliest stage of cortical processing. However, a debate regarding the proposed mechanism underlying perceptual learning is an ongoing issue. Nevertheless, generalization of a trained task to other functions is an important key, for both understanding the neural mechanisms and the practical value of the training. This manuscript describes a structured perceptual learning method that previously used (amblyopia, myopia) and a novel technique and results that were applied for presbyopia. In general, subjects were trained for contrast detection of Gabor targets under lateral masking conditions. Training improved contrast sensitivity and diminished the lateral suppression when it existed (amblyopia). The improvement was transferred to unrelated functions such as visual acuity. The new results of presbyopia show substantial improvement of the spatial and temporal contrast sensitivity, leading to improved processing speed of target detection as well as reaction time. Consequently, the subjects, who were able to eliminate the need for reading glasses, benefited. Thus, here we show that the transfer of functions indicates that the specificity of improvement in the trained task can be generalized by repetitive practice of target detection, covering a sufficient range of spatial frequencies and orientations, leading to an improvement in unrelated visual functions. Thus, perceptual learning can be a practical method to improve visual functions in people with impaired or blurred vision.
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Affiliation(s)
- Uri Polat
- Goldschleger Eye Research Institute, Tel Aviv University, Sheba Medical Center, Ramat Gan, 52621 Tel Hashomer, Israel.
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Abstract
Most studies on people with age-related macular degeneration (AMD) have been focused on investigations of low-level processes with simple stimuli like gratings, letters, and in perception of isolated faces or objects. We investigated the ability of people with low vision to analyze more complex stimuli like photographs of natural scenes. Fifteen participants with AMD and low vision (acuity on the better eye <20/200) and 11 normally sighted age-matched controls took part in the study. They were presented with photographs of either colored or achromatic gray level scenes in one condition and with photographs of natural scenes versus isolated objects extracted from these scenes in another condition. The photographs were centrally displayed for 300 ms. In both conditions, observers were instructed to press a key when they saw a predefined target (a face or an animal). The target was present in half of the trials. Color facilitated performance in people with low vision, while equivalent performance was found for colored and achromatic pictures in normally sighted participants. Isolated objects were categorized more accurately than objects in scenes in people with low vision. No difference was found for normally sighted observers. The results suggest that spatial properties that facilitate image segmentation (e.g., color and reduced crowding) help object perception in people with low vision.
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Chung STL, Li RW, Levi DM. Learning to identify near-threshold luminance-defined and contrast-defined letters in observers with amblyopia. Vision Res 2008; 48:2739-50. [PMID: 18824189 PMCID: PMC2642955 DOI: 10.1016/j.visres.2008.09.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 09/03/2008] [Accepted: 09/08/2008] [Indexed: 11/24/2022]
Abstract
We assessed whether or not the sensitivity for identifying luminance-defined and contrast-defined letters improved with training in a group of amblyopic observers who have passed the critical period of development. In Experiment 1, we tracked the contrast threshold for identifying luminance-defined letters with training in a group of 11 amblyopic observers. Following training, six observers showed a reduction in thresholds, averaging 20%, for identifying luminance-defined letters. This improvement transferred extremely well to the untrained task of identifying contrast-defined letters (average improvement=38%) but did not transfer to an acuity measurement. Seven of the 11 observers were subsequently trained on identifying contrast-defined letters in Experiment 2. Following training, five of these seven observers demonstrated a further improvement, averaging 17%, for identifying contrast-defined letters. This improvement did not transfer to the untrained task of identifying luminance-defined letters. Our findings are consistent with predictions based on the locus of learning for first- and second-order stimuli according to the filter-rectifier-filter model for second-order visual processing.
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Affiliation(s)
- Susana T L Chung
- School of Optometry, University of California, 360 Minor Hall, Berkeley, CA 94720-2020, USA.
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36
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Crowding between first- and second-order letters in amblyopia. Vision Res 2008; 48:788-98. [PMID: 18241910 DOI: 10.1016/j.visres.2007.12.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Revised: 12/07/2007] [Accepted: 12/14/2007] [Indexed: 11/20/2022]
Abstract
To test whether first- and second-order stimuli are processed independently in amblyopic vision, we measured thresholds for identifying a target letter flanked by two letters for all combinations of first- and second-order targets and flankers. We found that (1) the magnitude of crowding is greater for second- than for first-order letters for target and flankers of the same order type; (2) substantial but asymmetric cross-over crowding occurs such that stronger crowding is found for a second-order letter flanked by first-order letters than for the converse; (3) the spatial extent of crowding is independent of the order type of the letters. Our findings are consistent with the hypothesis that crowding results from an abnormal integration of target and flankers beyond the stage of feature detection, which takes place over a large distance in amblyopic vision.
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37
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Levi DM. Crowding--an essential bottleneck for object recognition: a mini-review. Vision Res 2008; 48:635-54. [PMID: 18226828 DOI: 10.1016/j.visres.2007.12.009] [Citation(s) in RCA: 556] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2007] [Revised: 11/30/2007] [Accepted: 12/11/2007] [Indexed: 11/19/2022]
Abstract
Crowding, generally defined as the deleterious influence of nearby contours on visual discrimination, is ubiquitous in spatial vision. Crowding impairs the ability to recognize objects in clutter. It has been extensively studied over the last 80 years or so, and much of the renewed interest is the hope that studying crowding may lead to a better understanding of the processes involved in object recognition. Crowding also has important clinical implications for patients with macular degeneration, amblyopia and dyslexia. There is no shortage of theories for crowding-from low-level receptive field models to high-level attention. The current picture is that crowding represents an essential bottleneck for object perception, impairing object perception in peripheral, amblyopic and possibly developing vision. Crowding is neither masking nor surround suppression. We can localize crowding to the cortex, perhaps as early as V1; however, there is a growing consensus for a two-stage model of crowding in which the first stage involves the detection of simple features (perhaps in V1), and a second stage is required for the integration or interpretation of the features as an object beyond V1. There is evidence for top-down effects in crowding, but the role of attention in this process remains unclear. The strong effect of learning in shrinking the spatial extent of crowding places strong constraints on possible models for crowding and for object recognition. The goal of this review is to try to provide a broad, balanced and succinct review that organizes and summarizes the diverse and scattered studies of crowding, and also helps to explain it to the non-specialist. A full understanding of crowding may allow us to understand this bottleneck to object recognition and the rules that govern the integration of features into objects.
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Affiliation(s)
- Dennis M Levi
- University of California at Berkeley, School of Optometry and The Helen Wills Neuroscience Institute, Berkeley, CA 94720-2020, USA.
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Bonneh YS, Sagi D, Polat U. Spatial and temporal crowding in amblyopia. Vision Res 2007; 47:1950-62. [PMID: 17502115 DOI: 10.1016/j.visres.2007.02.015] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 02/06/2007] [Accepted: 02/06/2007] [Indexed: 10/23/2022]
Abstract
Spatial crowding is a well-known deficit in amblyopia. We have previously reported evidence suggesting that the inability to isolate stimuli in space in crowded displays (spatial crowding) is a largely independent component of the amblyopic deficit in visual acuity, which is typically found in strabismic amblyopia [Bonneh, Y., Sagi, D., & Polat, U. (2004a). Local and non-local deficits in amblyopia: Acuity and spatial interactions. Vision Research, 44, 3009-3110]. Here, we extend this result to the temporal domain by measuring visual acuity (VA) for a single pattern in a rapid serial visual presentation (RSVP-VA, N=15) for fast ("crowded") and slow ("uncrowded") presentations. We found that strabismic amblyopes but not anisometropic amblyopes or normal controls exhibited a significant difference between VA under the fast and slow conditions. We further compared the "temporal crowding" measure to two measures of spatial crowding: (1) static Tumbling-E acuity in multi-pattern crowded displays (N=26) and (2) Gabor alignment with lateral flankers (N=20). We found that all three measures of crowding (one temporal and two spatial) were highly correlated across subjects while being largely independent of the visual acuity for a single isolated pattern, with both spatial and temporal crowding being high and correlated in strabismus and low in anisometropia. This suggests that time and space are related in crowding, at least in amblyopia.
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Affiliation(s)
- Yoram S Bonneh
- Department of Neurobiology, Brain Research, The Weizmann Institute of Science, Rehovot 76100, Israel.
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Levi DM, Yu C, Kuai SG, Rislove E. Global contour processing in amblyopia. Vision Res 2007; 47:512-24. [PMID: 17223155 PMCID: PMC1851910 DOI: 10.1016/j.visres.2006.10.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Revised: 10/19/2006] [Accepted: 10/23/2006] [Indexed: 11/19/2022]
Abstract
The purpose of the experiments described here was to investigate global image processing using methods that require global processing while eliminating or compensating for low level abnormalities: visibility, shape perception and positional uncertainty. In order to accomplish this we used a closed figure made up of Gabor patches either in noise or on a blank field. The stimuli were circular or elliptical contours, formed by N equally spaced Gabor patches. We performed two separate experiments: In one experiment we fixed N and varied the aspect ratio using a staircase to determine the threshold aspect ratio; in the second experiment we held the aspect ratio constant (at twice the threshold aspect ratio) and varied N in order to measure the threshold number of elements required to judge the shape. Our results confirm and extend previous studies showing that humans with naturally occurring amblyopia show deficits in contour processing. Our results show that the deficits depend strongly on spatial scale (target size and spatial frequency). The deficit in global contour processing is substantially greater in noise (where contour-linking is required) than on a blank field. The magnitude of the deficits is modest when low-level deficits (reduced visibility, increased positional uncertainty, and abnormal shape perception) are minimized, and does not seem to depend much on acuity, crowding or stereoacuity. The residual deficits reported here cannot be simply ascribed to reduced visibility or increased positional uncertainty, and we therefore conclude that these are genuine deficits in global contour segregation and integration.
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Affiliation(s)
- Dennis M Levi
- School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720-2020, USA.
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Abstract
Playing action video games enhances several different aspects of visual processing; however, the mechanisms underlying this improvement remain unclear. Here we show that playing action video games can alter fundamental characteristics of the visual system, such as the spatial resolution of visual processing across the visual field. To determine the spatial resolution of visual processing, we measured the smallest distance a distractor could be from a target without compromising target identification. This approach exploits the fact that visual processing is hindered as distractors are brought close to the target, a phenomenon known as crowding. Compared with nonplayers, action-video-game players could tolerate smaller target-distractor distances. Thus, the spatial resolution of visual processing is enhanced in this population. Critically, similar effects were observed in non-video-game players who were trained on an action video game; this result verifies a causative relationship between video-game play and augmented spatial resolution.
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Affiliation(s)
- C S Green
- Department of Brain and Cognitive Sciences, University of Rochester, NY 14627-0268, USA.
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Ho CS, Paul PS, Asirvatham A, Cavanagh P, Cline R, Giaschi DE. Abnormal spatial selection and tracking in children with amblyopia. Vision Res 2006; 46:3274-83. [PMID: 16774773 DOI: 10.1016/j.visres.2006.03.029] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 02/22/2006] [Accepted: 03/06/2006] [Indexed: 11/24/2022]
Abstract
We assessed 18 children with unilateral amblyopia and 30 age-matched controls on one low-level and three high-level motion tasks. Children with amblyopia showed similar performance to controls in both amblyopic and fellow eyes on a low-level global motion task and on a high-level 2-dot apparent motion task. Performance on both single-object and multiple-object attentive tracking tasks was significantly depressed in both amblyopic and fellow eyes relative to controls. These findings suggest that binocular regions of posterior parietal cortex likely contribute to a deficit in voluntary, spatial attention that is a component of amblyopia.
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Affiliation(s)
- C S Ho
- Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, BC, Canada
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Lerner Y, Hendler T, Malach R, Harel M, Leiba H, Stolovitch C, Pianka P. Selective fovea-related deprived activation in retinotopic and high-order visual cortex of human amblyopes. Neuroimage 2006; 33:169-79. [PMID: 16919483 DOI: 10.1016/j.neuroimage.2006.06.026] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 06/20/2006] [Accepted: 06/22/2006] [Indexed: 11/23/2022] Open
Abstract
Amblyopia is a visual disorder starting at early childhood and characterized by reduced visual acuity not of optical origin or due to any eye disease. One expression of such an anomalous early visual experience is abnormal foveal vision. In a previous fMRI study, faces that were presented to amblyopic eyes evoked little response compared to houses in high-order visual areas. Patients also demonstrated reduced recognition of facial expression, raising the possibility that these face-selective abnormalities are related to foveal vision deficit. Whether this deficit originates in low-level processing or is mediated by compromised activation in high-order visual areas is unresolved. In the present functional magnetic resonance imaging (fMRI) study, we explored the impact of amblyopia on the representation of object images presented in foveally biased central versus peripheral retinotopic eccentricities through manipulation of object size. Small and large pictures were correlated to visual acuities of 6/6 and 6/60, respectively. In low-level visual areas, the amblyopic eye showed significantly reduced activation for centrally placed, small pictures than the sound eye, while activation to large pictures was only slightly reduced. Similarly, in high-order visual areas, the amblyopic eye showed marked reduction in activation in the fusiform gyrus, with normal activation in the collateral sulcus. The center/periphery size-related amblyopic outcomes of this study support a "bottom-up" nature of the center-periphery effect observed in high-order visual areas. Taken together, these findings point to the regional extent and functional selectivity of fovea-related cortical reorganization that is related to abnormal visual development of one eye.
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Affiliation(s)
- Y Lerner
- Weizmann Institute of Science, Rehovot 76100, Israel
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Abstract
In the past five years, substantial progress has been made in our knowledge of the neural basis of amblyopia. Recent advances based on animal models are described, along with new psychophysical data showing perceptual deficits in amblyopic animals that are not explained by simple losses in contrast sensitivity. Studies of contour integration and integration of motion and form signals in the presence of noise show that 1) there are fundamental losses in temporal as well as spatial vision, 2) the losses extend to the fellow eye in many cases, 3) amblyopic animals are especially impaired in the presence of background noise, and 4) these losses must depend on a process downstream from area V1 in the extrastriate cortex.
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Affiliation(s)
- Lynne Kiorpes
- Center for Neural Science, New York University, New York, NY 10003, USA.
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Vlaskamp BNS, Hooge ITC. Crowding degrades saccadic search performance. Vision Res 2006; 46:417-25. [PMID: 15893785 DOI: 10.1016/j.visres.2005.04.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2005] [Revised: 04/05/2005] [Accepted: 04/07/2005] [Indexed: 11/17/2022]
Abstract
The identity of a target is more difficult to acquire when it is surrounded by distracters. The purpose of the present experiments was to investigate the implications of this crowding phenomenon for performance and eye movements in a real-life task as search with eye movements. The participants searched for a target in a one dimensional search strip. Above and below this search strip additional elements were added. In three conditions, the similarity of these mask elements to the search elements was varied. The spatial extent of crowding is known to increase with target-mask similarity [Nazir, T. A. (1992). Effects of lateral masking and spatial precueing on gap-resolution in central and peripheral vision. Vision Research, 32, 771-777, Kooi, F. L., Toet, A., Tripathy, S. P., & Levi, D. M. (1994). The effect of similarity and duration on spatial interaction in peripheral vision. Spatial Vision, 8(2), 255-279]. One condition did not contain masks. In a visibility experiment, we firstly validated this crowding manipulation. In the search experiment, we subsequently found that with increasing crowding search times were up to 76% longer. Eye movements were also affected. The number of fixations and fixation duration increased and saccade amplitude decreased with increasing crowding. We conclude that in order to understand eye movements in (everyday) tasks that require active exploration of the visual scene, crowding should be taken into account.
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Affiliation(s)
- Björn N S Vlaskamp
- Psychonomics, Helmholtz Institute, Universiteit Utrecht, Heidelberglaan 2, NL-3584 CS Utrecht, The Netherlands.
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