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Li Y, Dai W, Wang T, Wu Y, Dou F, Xing D. Visual surround suppression at the neural and perceptual levels. Cogn Neurodyn 2024; 18:741-756. [PMID: 38699623 PMCID: PMC11061091 DOI: 10.1007/s11571-023-10027-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2023] [Revised: 10/10/2023] [Accepted: 10/23/2023] [Indexed: 05/05/2024] Open
Abstract
Surround suppression was initially identified as a phenomenon at the neural level in which stimuli outside the neuron's receptive field alone cannot activate responses but can modulate neural responses to stimuli covered inside the receptive field. Subsequent studies showed that surround suppression is not only a critical property of neurons across species and brain areas but also has been found in visual perceptions. More importantly, surround suppression varies across individuals and shows significant differences between normal controls and patients with certain mental disorders. Here, we combined results from related literature and summarized the findings derived from physiological and psychophysical evidence. We first outline the basic properties of surround suppression in the visual system and perceptions. Then, we mainly summarize the differences in perceptual surround suppression among different human subjects. Our review suggests that there is no consensus regarding whether the strength of perceptual surround suppression could be used as an effective index to distinguish particular populations. Then, we summarized the similar mechanisms for surround suppression and cognitive impairments to further explore the potential clinical applications of surround suppression. A clearer understanding of the mechanisms of surround suppression in neural responses and perceptions is necessary for facilitating its clinical applications.
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Affiliation(s)
- Yang Li
- School of Criminology, People’s Public Security University of China, Beijing, 100038 China
| | - Weifeng Dai
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing, 100875 China
| | - Tian Wang
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing, 100875 China
- College of Life Sciences, Beijing Normal University, Beijing, 100875 China
| | - Yujie Wu
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing, 100875 China
| | - Fei Dou
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing, 100875 China
- College of Life Sciences, Beijing Normal University, Beijing, 100875 China
| | - Dajun Xing
- State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University, Beijing, 100875 China
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2
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Chen L, Chen G, Gong X, Fang F. Integrating electric field modeling and pre-tDCS behavioral performance to predict the individual tDCS effect on visual crowding. J Neural Eng 2023; 20:056019. [PMID: 37750681 DOI: 10.1088/1741-2552/acfa8c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 09/15/2023] [Indexed: 09/27/2023]
Abstract
Objective.Transcranial direct current stimulation (tDCS) has been broadly used to modulate brain activity with both bipolar and high-definition montages. However, tDCS effects can be highly variable. In this work, we investigated whether the variability in the tDCS effects could be predicted by integrating individualized electric field modeling and individual pre-tDCS behavioral performance.Approach.Here, we first compared the effects of bipolar tDCS and 4 × 1 high-definition tDCS (HD-tDCS) with respect to the alleviation of visual crowding, which is the inability to identify targets in the presence of nearby flankers and considered to be an essential bottleneck of object recognition and visual awareness. We instructed subjects to perform an orientation discrimination task with both isolated and crowded targets in the periphery and measured their orientation discrimination thresholds before and after receiving 20 min of bipolar tDCS, 4 × 1 HD-tDCS, or sham stimulation over the visual cortex. Individual anatomically realistic head models were constructed to simulate tDCS-induced electric field distributions and quantify tDCS focality. Finally, a multiple linear regression model that used pre-tDCS behavioral performance and tDCS focality as factors was used to predict post-tDCS behavioral performance.Main results.We found that HD-tDCS, but not bipolar tDCS, could significantly alleviate visual crowding. Moreover, the variability in the tDCS effect could be reliably predicted by subjects' pre-tDCS behavioral performance and tDCS focality. This prediction model also performed well when generalized to other two tDCS protocols with a different electrode size or a different stimulation intensity.Significance.Our study links the variability in the tDCS-induced electric field and the pre-tDCS behavioral performance in a visual crowding task to the variability in post-tDCS performance. It provides a new approach to predicting individual tDCS effects and highlights the importance of understanding the factors that determine tDCS effectiveness while developing more robust protocols.
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Affiliation(s)
- Luyao Chen
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing 100871, People's Republic of China
- Beijing Academy of Artificial Intelligence, Beijing 100084, People's Republic of China
- IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, People's Republic of China
- Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing 100871, People's Republic of China
| | - Guanpeng Chen
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing 100871, People's Republic of China
- IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, People's Republic of China
- Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing 100871, People's Republic of China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Xizi Gong
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing 100871, People's Republic of China
- IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, People's Republic of China
- Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing 100871, People's Republic of China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Fang Fang
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing 100871, People's Republic of China
- Beijing Academy of Artificial Intelligence, Beijing 100084, People's Republic of China
- IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, People's Republic of China
- Key Laboratory of Machine Perception (Ministry of Education), Peking University, Beijing 100871, People's Republic of China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
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3
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Kurzawski JW, Burchell A, Thapa D, Winawer J, Majaj NJ, Pelli DG. The Bouma law accounts for crowding in 50 observers. J Vis 2023; 23:6. [PMID: 37540179 PMCID: PMC10408772 DOI: 10.1167/jov.23.8.6] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 05/16/2023] [Indexed: 08/05/2023] Open
Abstract
Crowding is the failure to recognize an object due to surrounding clutter. Our visual crowding survey measured 13 crowding distances (or "critical spacings") twice in each of 50 observers. The survey includes three eccentricities (0, 5, and 10 deg), four cardinal meridians, two orientations (radial and tangential), and two fonts (Sloan and Pelli). The survey also tested foveal acuity, twice. Remarkably, fitting a two-parameter model-the well-known Bouma law, where crowding distance grows linearly with eccentricity-explains 82% of the variance for all 13 × 50 measured log crowding distances, cross-validated. An enhanced Bouma law, with factors for meridian, crowding orientation, target kind, and observer, explains 94% of the variance, again cross-validated. These additional factors reveal several asymmetries, consistent with previous reports, which can be expressed as crowding-distance ratios: 0.62 horizontal:vertical, 0.79 lower:upper, 0.78 right:left, 0.55 tangential:radial, and 0.78 Sloan-font:Pelli-font. Across our observers, peripheral crowding is independent of foveal crowding and acuity. Evaluation of the Bouma factor, b (the slope of the Bouma law), as a biomarker of visual health would be easier if there were a way to compare results across crowding studies that use different methods. We define a standardized Bouma factor b' that corrects for differences from Bouma's 25 choice alternatives, 75% threshold criterion, and linearly symmetric flanker placement. For radial crowding on the right meridian, the standardized Bouma factor b' is 0.24 for this study, 0.35 for Bouma (1970), and 0.30 for the geometric mean across five representative modern studies, including this one, showing good agreement across labs, including Bouma's. Simulations, confirmed by data, show that peeking can skew estimates of crowding (e.g., greatly decreasing the mean or doubling the SD of log b). Using gaze tracking to prevent peeking, individual differences are robust, as evidenced by the much larger 0.08 SD of log b across observers than the mere 0.03 test-retest SD of log b measured in half an hour. The ease of measurement of crowding enhances its promise as a biomarker for dyslexia and visual health.
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Affiliation(s)
- Jan W Kurzawski
- Department of Psychology, New York University, New York, NY, USA
| | - Augustin Burchell
- Cognitive Science & Computer Science, Swarthmore College, Swarthmore, PA, USA
| | - Darshan Thapa
- Center for Neural Science, New York University, New York, NY, USA
| | - Jonathan Winawer
- Department of Psychology, New York University, New York, NY, USA
- Center for Neural Science, New York University, New York, NY, USA
| | - Najib J Majaj
- Center for Neural Science, New York University, New York, NY, USA
| | - Denis G Pelli
- Department of Psychology, New York University, New York, NY, USA
- Center for Neural Science, New York University, New York, NY, USA
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4
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Chien SE, Yang YH, Ono Y, Yeh SL. Theta activity in semantic priming under visual crowding as revealed by magnetoencephalography. Neurosci Res 2022; 185:29-39. [PMID: 36113812 DOI: 10.1016/j.neures.2022.09.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2021] [Revised: 08/29/2022] [Accepted: 09/11/2022] [Indexed: 11/27/2022]
Abstract
Crowding refers to impaired object recognition of peripheral visual targets caused by nearby flankers. It has been shown that the response to a word was faster when it was preceded by a semantically related than unrelated crowded prime, demonstrating that semantic priming survives crowding. This study examines neural correlates of semantic priming under visual crowding using magnetoencephalography with four conditions: prime (isolated, crowded) x prime-target relationship (related, unrelated). Participants judged whether the target was a word or a nonword. We found significant differences in θ activity at the left inferior frontal gyrus (IFG) for both isolated and crowded primes when comparing the unrelated and related conditions, although the activation was delayed with the crowded prime compared to the isolated prime. The locations within the IFG were also different: theta-band activation was at BA 45 in the isolated condition and at BA 47 in the crowded condition. Phase-locking-value analysis revealed that bilateral IFG was more synchronized with unrelated prime-target pairs than related pairs regardless of whether the primes were isolated or crowded, indicating the recruitment of the right hemisphere when the prime-target semantic relationship was remote. Finally, the distinct waveform patterns found in the isolated and crowded conditions from both the source localization and PLV analysis suggest different neural mechanisms for processing semantic information with isolated primes versus crowded primes.
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Affiliation(s)
- Sung-En Chien
- Department of Psychology, National Taiwan University, Taipei, Taiwan
| | - Yung-Hao Yang
- Department of Psychology, National Taiwan University, Taipei, Taiwan
| | - Yumie Ono
- School of Science and Technology, Meiji University, Kanagawa, Japan
| | - Su-Ling Yeh
- Department of Psychology, National Taiwan University, Taipei, Taiwan; Graduate Institute of Brain and Mind Sciences, National Taiwan University, Taipei, Taiwan; Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan; Center for Artificial Intelligence and Advanced Robotics, National Taiwan University, Taipei, Taiwan.
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5
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Unraveling brain interactions in vision: The example of crowding. Neuroimage 2021; 240:118390. [PMID: 34271157 DOI: 10.1016/j.neuroimage.2021.118390] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 07/09/2021] [Accepted: 07/12/2021] [Indexed: 11/22/2022] Open
Abstract
Crowding, the impairment of target discrimination in clutter, is the standard situation in vision. Traditionally, crowding is explained with (feedforward) models, in which only neighboring elements interact, leading to a "bottleneck" at the earliest stages of vision. It is with this implicit prior that most functional magnetic resonance imaging (fMRI) studies approach the identification of the "neural locus" of crowding, searching for the earliest visual area in which the blood-oxygenation-level-dependent (BOLD) signal is suppressed under crowded conditions. Using this classic approach, we replicated previous findings of crowding-related BOLD suppression starting in V2 and increasing up the visual hierarchy. Surprisingly, under conditions of uncrowding, in which adding flankers improves performance, the BOLD signal was further suppressed. This suggests an important role for top-down connections, which is in line with global models of crowding. To discriminate between various possible models, we used dynamic causal modeling (DCM). We show that recurrent interactions between all visual areas, including higher-level areas like V4 and the lateral occipital complex (LOC), are crucial in crowding and uncrowding. Our results explain the discrepancies in previous findings: in a recurrent visual hierarchy, the crowding effect can theoretically be detected at any stage. Beyond crowding, we demonstrate the need for models like DCM to understand the complex recurrent processing which most likely underlies human perception in general.
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6
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Chen G, Zhu Z, He Q, Fang F. Offline transcranial direct current stimulation improves the ability to perceive crowded targets. J Vis 2021; 21:1. [PMID: 33533878 PMCID: PMC7862736 DOI: 10.1167/jov.21.2.1] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The deleterious effect of nearby flankers on target identification in the periphery is known as visual crowding. Studying visual crowding can advance our understanding of the mechanisms of visual awareness and object recognition. Alleviating visual crowding is one of the major ways to improve peripheral vision. The aim of the current study was to examine whether transcranial direct current stimulation (tDCS) was capable of alleviating visual crowding at different visual eccentricities and with different visual tasks. In the present single-blind sham-controlled study, subjects were instructed to perform an orientation discrimination task or a letter identification task with isolated and crowded targets in the periphery, before and after applying 20 minutes of 2 mA anodal tDCS to visual cortex of the hemisphere contralateral or ipsilateral to visual stimuli. Contralateral tDCS significantly alleviated the orientation crowding effect at two different eccentricities and the letter crowding effect. This alleviation was absent after sham or ipsilateral stimulation and could not be fully explained by the performance improvement with the isolated targets. These findings demonstrated that offline tDCS was effective in alleviating visual crowding across different visual eccentricities and tasks, therefore providing a promising way to improve spatial vision rapidly in crowded scenes.
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Affiliation(s)
- Guanpeng Chen
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, People's Republic of China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, People's Republic of China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, People's Republic of China.,
| | - Ziyun Zhu
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, People's Republic of China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, People's Republic of China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, People's Republic of China.,
| | - Qing He
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, People's Republic of China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, People's Republic of China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, People's Republic of China.,
| | - Fang Fang
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, People's Republic of China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, People's Republic of China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, People's Republic of China.,
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7
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Strappini F, Martelli M, Cozzo C, di Pace E. Empirical Evidence for Intraspecific Multiple Realization? Front Psychol 2020; 11:1676. [PMID: 32793053 PMCID: PMC7394053 DOI: 10.3389/fpsyg.2020.01676] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Accepted: 06/19/2020] [Indexed: 11/13/2022] Open
Abstract
Despite the remarkable advances in behavioral and brain sciences over the last decades, the mind-body (brain) problem is still an open debate and one of the most intriguing questions for both cognitive neuroscience and philosophy of mind. Traditional approaches have conceived this problem in terms of a contrast between physicalist monism and Cartesian dualism. However, since the late sixties, the landscape of philosophical views on the problem has become more varied and complex. The Multiple Realization Thesis (MRT) claims that mental properties can be (or are) realized, and mental processes can be (or are) implemented by neural correlates of different kinds. Thus, MRT challenges the psychoneural type-identity theory and the corresponding reductionism. Many philosophers have acknowledged the a priori plausibility of MRT. However, the existence of empirical evidence in favor of intraspecific, human multiple realizations of mental processes and properties is still controversial. Here, we illustrate some cases that provide empirical evidence in support of MRT. Recently, it has been proposed that foveal agnosic vision, like peripheral vision, can be restored by increasing object parts’ spacing (Crutch and Warrington, 2007; Strappini et al., 2017b). Agnosic fovea and normal periphery are both limited by crowding, which impairs object recognition, and provides the signature of visual integration. Here, we define a psychological property of restored object identification, and we cross-reference the data of visually impaired patients with different etiologies. In particular, we compare the data of two stroke patients, two patients with posterior cortical atrophy, six cases of strabismic amblyopia, and one case with restored sight. We also compare these patients with unimpaired subjects tested in the periphery. We show that integration (i.e., restored recognition) seems to describe quite accurately the visual performance in all these cases. Whereas the patients have different etiologies and different neural correlates, the unimpaired subjects have no neural damage. Thus, similarity in the psychological property given the differences in the neural substrate can be interpreted in relation to MRT and provide evidence in its support. Finally, we will frame our contribution within the current debate concerning MRT providing new and compelling empirical evidence.
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Affiliation(s)
| | | | - Cesare Cozzo
- Department of Philosophy, Sapienza University of Rome, Rome, Italy
| | - Enrico di Pace
- Department of Psychology, Sapienza University of Rome, Rome, Italy
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8
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Roumani D, Moutoussis K. Invisible Adaptation: The Effect of Awareness on the Strength of the Motion Aftereffect. Perception 2020; 49:835-857. [PMID: 32605425 DOI: 10.1177/0301006620936853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The ability to process information despite the lack of perceptual awareness is one of the most fascinating aspects of the visual system. Such unconscious processing is often investigated using adaptation, where any presence of the former can be traced by its footprint on aftereffects following the latter. We have investigated the mechanisms of the motion aftereffect (MAE) using random dot displays of varying motion coherence as well as crowding to modulate both the physical as well as the perceptual strength of the adaptation stimulus. Perceptual strength was quantitatively measured as the performance in a forced-choice direction-discrimination task. A motion-nulling technique was used to quantitatively measure the strength of the MAE. We show that the strength of the dynamic MAE is independently influenced by both the physical stimulus strength as well as the subjective perceptual strength, with the effect of the former being more prominent than that of the latter. We further show that the MAE still persists under conditions of subthreshold perception. Our results suggest that perceptual awareness can influence the strength of visual processing, but the latter is not fully dependent on the former and can still take place at its partial or even total absence.
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Affiliation(s)
- Daphne Roumani
- Cognitive Science Division, Department of Philosophy and History of Science, National and Kapodistrian University of Athens, Greece
| | - Konstantinos Moutoussis
- Cognitive Science Division, Department of Philosophy and History of Science, National and Kapodistrian University of Athens, Greece
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9
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Henry CA, Kohn A. Spatial contextual effects in primary visual cortex limit feature representation under crowding. Nat Commun 2020; 11:1687. [PMID: 32245941 PMCID: PMC7125172 DOI: 10.1038/s41467-020-15386-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 03/09/2020] [Indexed: 12/25/2022] Open
Abstract
Crowding is a profound loss of discriminability of visual features, when a target stimulus is surrounded by distractors. Numerous studies of human perception have characterized how crowding depends on the properties of a visual display. Yet, there is limited understanding of how and where stimulus information is lost in the visual system under crowding. Here, we show that macaque monkeys exhibit perceptual crowding for target orientation that is similar to humans. We then record from neuronal populations in monkey primary visual cortex (V1). These populations show an appreciable loss of information about target orientation in the presence of distractors, due both to divisive and additive modulation of responses to targets by distractors. Our results show that spatial contextual effects in V1 limit the discriminability of visual features and can contribute substantively to crowding. Visual crowding can strongly limit perceptual discriminability, yet its neural basis remains unclear. Here, the authors show that perceptual crowding is similar in monkeys and humans, and that feature encoding in neuronal populations in primary visual cortex is limited for displays inducing crowding.
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Affiliation(s)
- Christopher A Henry
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, 10461, USA.
| | - Adam Kohn
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, 10461, USA.,Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, NY, 10461, USA.,Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, NY, 10461, USA
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10
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Separation effect of early visual cortex V1 under different crowding conditions: a transcranial magnetic stimulation study. Neuroreport 2019; 30:974-979. [PMID: 31469722 DOI: 10.1097/wnr.0000000000001316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The visual crowding makes it difficult to identify the patterns in peripheral vision, but the neural mechanism for this phenomenon is still unclear because of different opinions. To study the separation effect of early visual cortex V1 under different crowding conditions, single-pulse transcranial magnetic stimulation (TMS) is applied within the right V1. The experimental design includes two factors: TMS intensity (10%, 65%, and 90% of the phosphene threshold) and crowding conditions (high and low). The accuracy results show that there is a strong interaction between crowding and TMS conditions. When the TMS intensity is 65% or 90% of the phosphene threshold, more crowding will be perceived under the high crowding condition, and less crowding under the low crowding condition. We concluded that the high and the low crowding conditions can be separated by TMS. These results support the assumption that the crowding is related to V1 and occurs in the visual coding phase.
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11
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Han Q, Luo H. Visual crowding involves delayed frontoparietal response and enhanced top-down modulation. Eur J Neurosci 2019; 50:2931-2941. [PMID: 30864167 DOI: 10.1111/ejn.14401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 02/15/2019] [Accepted: 03/05/2019] [Indexed: 11/26/2022]
Abstract
Crowding, the disrupted recognition of a peripheral target in the presence of nearby flankers, sets a fundamental limit on peripheral vision perception. Debates persist on whether the limit occurs at early visual cortices or is induced by top-down modulation, leaving the neural mechanism for visual crowding largely unclear. To resolve the debate, it is crucial to extract the neural signals elicited by the target from that by the target-flanker clutter, with high temporal resolution. To achieve this purpose, here we employed a temporal response function (TRF) approach to dissociate target-specific response from the overall electroencephalograph (EEG) recordings when the target was presented with (crowded) or without flankers (uncrowded) while subjects were performing a discrimination task on the peripherally presented target. Our results demonstrated two components in the target-specific contrast-tracking TRF response-an early component (100-170 ms) in occipital channels and a late component (210-450 ms) in frontoparietal channels. The late frontoparietal component, which was delayed in time under the crowded condition, was correlated with target discrimination performance, suggesting its involvement in visual crowding. Granger causality analysis further revealed stronger top-down modulation on the target stimulus under the crowded condition. Taken together, our findings support that crowding is associated with a top-down process which modulates the low-level sensory processing and delays the behavioral-relevant response in the high-level region.
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Affiliation(s)
- Qiming Han
- School of Psychological and Cognitive Sciences, Peking University, Beijing, China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, China.,Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Huan Luo
- School of Psychological and Cognitive Sciences, Peking University, Beijing, China.,IDG/McGovern Institute for Brain Research, Peking University, Beijing, China.,Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, China
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12
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Cortical Reorganization of Peripheral Vision Induced by Simulated Central Vision Loss. J Neurosci 2019; 39:3529-3536. [PMID: 30814310 DOI: 10.1523/jneurosci.2126-18.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 01/29/2019] [Accepted: 02/21/2019] [Indexed: 11/21/2022] Open
Abstract
When one's central vision is deprived, a spared part of the peripheral retina acts as a pseudofovea for fixation. The neural mechanisms underlying this compensatory adjustment remain unclear. Here we report cortical reorganization induced by simulated central vision loss. Human subjects of both sexes learned to place the target at an eccentric retinal locus outside their blocked visual field for object tracking. Before and after training, we measured visual crowding-a bottleneck of object identification in peripheral vision, using psychophysics and fMRI. We found that training led to an axis-specific reduction of crowding. The change of the crowding effect was reflected in the change of BOLD signal, as a release of cortical suppression in multiple visual areas starting as early as V1. Our findings suggest that the adult visual system is capable of reshaping its oculomotor control and sensory coding to adapt to impoverished visual input.SIGNIFICANCE STATEMENT By simulating central vision loss in normally sighted adults, we found that oculomotor training not only induces PRL, but also facilitates form processing in peripheral vision. As subjects learned to place the target at an eccentric retinal locus, "visual crowding"-the detrimental effect of clutter on peripheral object identification-was reduced. The reduction of the crowding effect was accompanied by a release of response suppression in the visual cortex. These findings indicate that the adult visual system is capable of reshaping the peripheral vision to adapt to central vision loss.
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13
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Contextual-Dependent Attention Effect on Crowded Orientation Signals in Human Visual Cortex. J Neurosci 2018; 38:8433-8440. [PMID: 30120209 DOI: 10.1523/jneurosci.0805-18.2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 08/03/2018] [Accepted: 08/07/2018] [Indexed: 11/21/2022] Open
Abstract
A target becomes hard to identify with nearby visual stimuli. This phenomenon, known as crowding, places a fundamental limit on conscious perception and object recognition. To understand the neural representation of crowded stimuli, we used fMRI and a forward encoding model to reconstruct the target-specific feature from multivoxel activation patterns evoked by orientation patches. Orientation-selective response profiles were constructed in V1-V4 for a target embedded in different contexts. Subjects of both sexes either directed their attention over all the orientation patches or selectively to the target. In the context with a weak crowding effect, attending to the target enhanced the orientation selectivity of the response profile; such effect increased along the visual pathway. In the context with a strong crowding effect, attending to the target enhanced the orientation selectivity of the response profile in the earlier visual area, but not in V4. The increase and decrease of orientation selectivity along the visual hierarchy demonstrate a contextual-dependent attention effect on crowded orientation signals: in the context with a weak crowding effect, selective attention gradually resolves the target from nearby distractors along the hierarchy; in the context with a strong crowding effect, while selective attention maintains the target feature in the earlier visual area, its effect decreases in the downstream area. Our findings reveal how the human visual system represents the target-specific feature at multiple stages under the limit of attention selection in a cluttered scene.SIGNIFICANCE STATEMENT Using fMRI and a forward encoding model, we reconstructed orientation-selective response profiles for a target embedded in crowded contexts. In the context with a weak crowding effect, attention gradually resolves the target from nearby distractors along the visual hierarchy. In the context with a strong crowding effect, while the feature of the target is preserved in the early visual cortex, it degrades in the later visual processing stage. The increase and decrease of orientation selectivity along the visual hierarchy reveal how the human visual system strikes to present the target-specific feature under the limit of attention selection in a cluttered scene.
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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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15
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Strappini F, Galati G, Martelli M, Di Pace E, Pitzalis S. Perceptual integration and attention in human extrastriate cortex. Sci Rep 2017; 7:14848. [PMID: 29093537 PMCID: PMC5665925 DOI: 10.1038/s41598-017-13921-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 10/04/2017] [Indexed: 11/29/2022] Open
Abstract
Visual crowding is a perceptual phenomenon with far-reaching implications in both perceptual (e.g., object recognition and reading) and clinical (e.g., developmental dyslexia and visual agnosia) domains. Here, we combined event-related fMRI measurements and wide-field brain mapping methods to investigate whether the BOLD response evoked by visual crowding is modulated by different attentional conditions. Participants underwent two sessions of psychophysical training outside the scanner, and then fMRI BOLD activity was measured simultaneously in early visual areas (including the visual word form area, VWFA), while they viewed strongly-crowded and weakly-crowded Gabor patches in attended and unattended conditions. We found that crowding increased BOLD activity in a network of areas including V1, V2, V3A, V4/V8, and VWFA. In V4/V8 and VWFA we found an increased activity related to attention. The effect of crowding in V1 was recorded only when attention was fully devoted to the target location. Our results provide evidence that some area beyond V1 might be the likely candidate for the site of crowding, thus supporting the view of visual crowding as a mid-level visual phenomenon.
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Affiliation(s)
- Francesca Strappini
- Neurobiology Department, Weizmann Institute of Science, Rehovot, Israel. .,Department of Psychology, Sapienza University, Rome, Italy. .,Neuropsychology Center, Santa Lucia Foundation, Rome, Italy.
| | - Gaspare Galati
- Department of Psychology, Sapienza University, Rome, Italy.,Neuropsychology Center, Santa Lucia Foundation, Rome, Italy
| | - Marialuisa Martelli
- Department of Psychology, Sapienza University, Rome, Italy.,Neuropsychology Center, Santa Lucia Foundation, Rome, Italy
| | - Enrico Di Pace
- Department of Psychology, Sapienza University, Rome, Italy
| | - Sabrina Pitzalis
- Neuropsychology Center, Santa Lucia Foundation, Rome, Italy.,Department of Education in Sport and Human Movement, University of Rome "Foro Italico", Rome, Italy
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16
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Ronconi L, Bellacosa Marotti R. Awareness in the crowd: Beta power and alpha phase of prestimulus oscillations predict object discrimination in visual crowding. Conscious Cogn 2017; 54:36-46. [DOI: 10.1016/j.concog.2017.04.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 04/26/2017] [Accepted: 04/29/2017] [Indexed: 12/23/2022]
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17
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Maniglia M, Cottereau BR, Soler V, Trotter Y. Rehabilitation Approaches in Macular Degeneration Patients. Front Syst Neurosci 2016; 10:107. [PMID: 28082876 PMCID: PMC5187382 DOI: 10.3389/fnsys.2016.00107] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 12/12/2016] [Indexed: 11/13/2022] Open
Abstract
Age related macular degeneration (AMD) is a visual disease that affects elderly population. It entails a progressive loss of central vision whose consequences are dramatic for the patient's quality of life. Current rehabilitation programs are restricted to technical aids based on visual devices. They only temporarily improve specific visual functions such as reading skills. Considering the rapid increase of the aging population worldwide, it is crucial to intensify clinical research on AMD in order to develop simple and efficient methods that improve the patient's visual performances in many different contexts. One very promising approach to face this challenge is based on perceptual learning (PL). Through intensive practice, PL can induce neural plasticity in sensory cortices and result in long-lasting enhancements for various perceptual tasks in both normal and visually impaired populations. A growing number of studies showed how appropriate PL protocols improve visual functions in visual disorders, namely amblyopia, presbyopia or myopia. In order to successfully apply these approaches to more severe conditions such as AMD, numerous challenges have to be overcome. Indeed, the overall elderly age of patients and the reduced cortical surface that is devoted to peripheral vision potentially limit neural plasticity in this population. In addition, ocular fixation becomes much less stable because patients have to rely on peripheral fixation spots outside the scotoma whose size keeps on evolving. The aim of this review article is to discuss the recent literature on this topic and to offer a unified approach for developing new rehabilitation programs of AMD using PL. We argue that with an appropriate experimental and training protocol that is adapted to each patient needs, PL can offer fascinating opportunities for the development of simple, non-expensive rehabilitation approaches a large spectrum of visual functions in AMD patients.
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Affiliation(s)
- Marcello Maniglia
- Centre de Recherche Cerveau et Cognition, Université de Toulouse-UPSToulouse, France; Centre National de la Recherche ScientifiqueToulouse, France; Department of Psychology, University of CaliforniaRiverside, CA, USA
| | - Benoit R Cottereau
- Centre de Recherche Cerveau et Cognition, Université de Toulouse-UPSToulouse, France; Centre National de la Recherche ScientifiqueToulouse, France
| | - Vincent Soler
- Department of Ophthalmology, Hopital CHU Purpan Toulouse, France
| | - Yves Trotter
- Centre de Recherche Cerveau et Cognition, Université de Toulouse-UPSToulouse, France; Centre National de la Recherche ScientifiqueToulouse, France
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18
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Ronconi L, Bertoni S, Bellacosa Marotti R. The neural origins of visual crowding as revealed by event-related potentials and oscillatory dynamics. Cortex 2016; 79:87-98. [DOI: 10.1016/j.cortex.2016.03.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 11/20/2015] [Accepted: 03/02/2016] [Indexed: 10/22/2022]
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19
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Yong K, Rajdev K, Warrington E, Nicholas J, Warren J, Crutch S. A longitudinal investigation of the relationship between crowding and reading: A neurodegenerative approach. Neuropsychologia 2016; 85:127-36. [PMID: 26926579 PMCID: PMC4863520 DOI: 10.1016/j.neuropsychologia.2016.02.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 02/23/2016] [Accepted: 02/26/2016] [Indexed: 11/24/2022]
Abstract
We have previously documented two patients (FOL and CLA) with posterior cortical atrophy who achieved accurate and rapid reading despite deficits in ten measures of visual processing, with two notable exceptions: (1) a measure of visual acuity, (2) a measure of visual crowding. Subsequent longitudinal investigation of these patients was carried out, involving annual tests of early visual, visuoperceptual and visuospatial processing and assessment of reading ability. Follow-up assessments identified the evolution of a particular early visual processing deficit, excessive visual crowding; this deficit has been previously implicated in forms of dyslexia. Consistent with the link between crowding and reading dysfunction, follow-up assessments also revealed deterioration in both patients' reading ability. The current findings demonstrate a neurodegenerative approach towards understanding the relationship between visual crowding and the reading system, and suggest possible mechanisms for how excessive crowding may disrupt word recognition.
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Affiliation(s)
- Keir Yong
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK.
| | - Kishan Rajdev
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK
| | - Elizabeth Warrington
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK
| | - Jennifer Nicholas
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK
| | - Jason Warren
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK
| | - Sebastian Crutch
- Dementia Research Centre, Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, UK
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20
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Does Temporal Integration Occur for Unrecognizable Words in Visual Crowding? PLoS One 2016; 11:e0149355. [PMID: 26890366 PMCID: PMC4758582 DOI: 10.1371/journal.pone.0149355] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Accepted: 01/29/2016] [Indexed: 11/19/2022] Open
Abstract
Visual crowding—the inability to see an object when it is surrounded by flankers in the periphery—does not block semantic activation: unrecognizable words due to visual crowding still generated robust semantic priming in subsequent lexical decision tasks. Based on the previous finding, the current study further explored whether unrecognizable crowded words can be temporally integrated into a phrase. By showing one word at a time, we presented Chinese four-word idioms with either a congruent or incongruent ending word in order to examine whether the three preceding crowded words can be temporally integrated to form a semantic context so as to affect the processing of the ending word. Results from both behavioral (Experiment 1) and Event-Related Potential (Experiment 2 and 3) measures showed congruency effect in only the non-crowded condition, which does not support the existence of unconscious multi-word integration. Aside from four-word idioms, we also found that two-word (modifier + adjective combination) integration—the simplest kind of temporal semantic integration—did not occur in visual crowding (Experiment 4). Our findings suggest that integration of temporally separated words might require conscious awareness, at least under the timing conditions tested in the current study.
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21
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Abstract
Crowding between adjacent letters has been investigated primarily as a spatial effect. The purpose of this study was to investigate the spatio-temporal properties of letter crowding. Specifically, we examined the systematic changes in the degradation effects in letter identification performance when adjacent letters were presented with a temporal asynchrony, as a function of letter separation and between the fovea and the periphery. We measured proportion-correct performance for identifying the middle target letter in strings of three lowercase letters at the fovea and 10° in the inferior visual field, for a range of center-to-center letter separations and a range of stimulus onset asynchronies (SOA) between the target and flanking letters (positive SOAs: target preceded flankers). As expected, the accuracy for identifying the target letters reduces with decreases in letter separation. This crowding effect shows a strong dependency on SOAs, such that crowding is maximal between 0 and ∼100 ms (depending on conditions) and diminishes for larger SOAs (positive or negative). Maximal crowding does not require the target and flanking letters to physically coexist for the entire presentation duration. Most importantly, crowding can be minimized even for closely spaced letters if there is a large temporal asynchrony between the target and flankers. The reliance of letter identification performance on SOAs and how it changes with letter separations imply that the crowding effect can be traded between space and time. Our findings are consistent with the notion that crowding should be considered as a spatio-temporal, and not simply a spatial, effect.
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22
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Abstract
In peripheral vision, objects that are easily discriminated on their own become less discriminable in the presence of surrounding clutter. This phenomenon is known as crowding.The neural mechanisms underlying crowding are not well understood. Better insight might come from single-neuron recording in nonhuman primates, provided they exhibit crowding; however, previous demonstrations of crowding have been confined to humans. In the present study, we set out to determine whether crowding occurs in rhesus macaque monkeys. We found that animals trained to identify a target letter among flankers displayed three hallmarks of crowding as established in humans. First, at a given eccentricity, increasing the spacing between the target and the flankers improved recognition accuracy. Second, the critical spacing, defined as the minimal spacing at which target discrimination was reliable, was proportional to eccentricity. Third, the critical spacing was largely unaffected by object size. We conclude that monkeys, like humans, experience crowding. These findings open the door to studies of crowding at the neuronal level in the monkey visual system.
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23
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Pavan A, Greenlee MW. Effects of crowding and attention on high-levels of motion processing and motion adaptation. PLoS One 2015; 10:e0117233. [PMID: 25615577 PMCID: PMC4304809 DOI: 10.1371/journal.pone.0117233] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Accepted: 12/12/2014] [Indexed: 11/18/2022] Open
Abstract
The motion after-effect (MAE) persists in crowding conditions, i.e., when the adaptation direction cannot be reliably perceived. The MAE originating from complex moving patterns spreads into non-adapted sectors of a multi-sector adapting display (i.e., phantom MAE). In the present study we used global rotating patterns to measure the strength of the conventional and phantom MAEs in crowded and non-crowded conditions, and when attention was directed to the adapting stimulus and when it was diverted away from the adapting stimulus. The results show that: (i) the phantom MAE is weaker than the conventional MAE, for both non-crowded and crowded conditions, and when attention was focused on the adapting stimulus and when it was diverted from it, (ii) conventional and phantom MAEs in the crowded condition are weaker than in the non-crowded condition. Analysis conducted to assess the effect of crowding on high-level of motion adaptation suggests that crowding is likely to affect the awareness of the adapting stimulus rather than degrading its sensory representation, (iii) for high-level of motion processing the attentional manipulation does not affect the strength of either conventional or phantom MAEs, neither in the non-crowded nor in the crowded conditions. These results suggest that high-level MAEs do not depend on attention and that at high-level of motion adaptation the effects of crowding are not modulated by attention.
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Affiliation(s)
- Andrea Pavan
- Universität Regensburg, Institut für Psychologie, Experimental and Clinical Neuroscience Study Programme, Universitätsstr. 31, 93053, Regensburg, Germany
- University of Lincoln, School of Psychology, Brayford Pool, Lincoln, LN6 7TS, United Kingdom
- * E-mail:
| | - Mark W. Greenlee
- Universität Regensburg, Institut für Psychologie, Experimental and Clinical Neuroscience Study Programme, Universitätsstr. 31, 93053, Regensburg, Germany
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24
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Kwon M, Bao P, Millin R, Tjan BS. Radial-tangential anisotropy of crowding in the early visual areas. J Neurophysiol 2014; 112:2413-22. [PMID: 25122703 PMCID: PMC4233277 DOI: 10.1152/jn.00476.2014] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 08/07/2014] [Indexed: 11/22/2022] Open
Abstract
Crowding, the inability to recognize an individual object in clutter (Bouma H. Nature 226: 177-178, 1970), is considered a major impediment to object recognition in peripheral vision. Despite its significance, the cortical loci of crowding are not well understood. In particular, the role of the primary visual cortex (V1) remains unclear. Here we utilize a diagnostic feature of crowding to identify the earliest cortical locus of crowding. Controlling for other factors, radially arranged flankers induce more crowding than tangentially arranged ones (Toet A, Levi DM. Vision Res 32: 1349-1357, 1992). We used functional magnetic resonance imaging (fMRI) to measure the change in mean blood oxygenation level-dependent (BOLD) response due to the addition of a middle letter between a pair of radially or tangentially arranged flankers. Consistent with the previous finding that crowding is associated with a reduced BOLD response [Millin R, Arman AC, Chung ST, Tjan BS. Cereb Cortex (July 5, 2013). doi:10.1093/cercor/bht159], we found that the BOLD signal evoked by the middle letter depended on the arrangement of the flankers: less BOLD response was associated with adding the middle letter between radially arranged flankers compared with adding it between tangentially arranged flankers. This anisotropy in BOLD response was present as early as V1 and remained significant in downstream areas. The effect was observed while subjects' attention was diverted away from the testing stimuli. Contrast detection threshold for the middle letter was unaffected by flanker arrangement, ruling out surround suppression of contrast response as a major factor in the observed BOLD anisotropy. Our findings support the view that V1 contributes to crowding.
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Affiliation(s)
- MiYoung Kwon
- Schepens Eye Research Institute/Massachusetts Eye and Ear Infirmary, Boston, Massachusetts; and Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
| | - Pinglei Bao
- Neuroscience Graduate Program, University of Southern California, Los Angeles, California
| | - Rachel Millin
- Neuroscience Graduate Program, University of Southern California, Los Angeles, California
| | - Bosco S Tjan
- Department of Psychology, University of Southern California, Los Angeles, California; Neuroscience Graduate Program, University of Southern California, Los Angeles, California;
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25
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Yong KXX, Shakespeare TJ, Cash D, Henley SMD, Nicholas JM, Ridgway GR, Golden HL, Warrington EK, Carton AM, Kaski D, Schott JM, Warren JD, Crutch SJ. Prominent effects and neural correlates of visual crowding in a neurodegenerative disease population. ACTA ACUST UNITED AC 2014; 137:3284-99. [PMID: 25351740 PMCID: PMC4240300 DOI: 10.1093/brain/awu293] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Crowding is a breakdown in the ability to identify objects in clutter, and is a major constraint on object recognition. Crowding particularly impairs object perception in peripheral, amblyopic and possibly developing vision. Here we argue that crowding is also a critical factor limiting object perception in central vision of individuals with neurodegeneration of the occipital cortices. In the current study, individuals with posterior cortical atrophy (n=26), typical Alzheimer's disease (n=17) and healthy control subjects (n=14) completed centrally-presented tests of letter identification under six different flanking conditions (unflanked, and with letter, shape, number, same polarity and reverse polarity flankers) with two different target-flanker spacings (condensed, spaced). Patients with posterior cortical atrophy were significantly less accurate and slower to identify targets in the condensed than spaced condition even when the target letters were surrounded by flankers of a different category. Importantly, this spacing effect was observed for same, but not reverse, polarity flankers. The difference in accuracy between spaced and condensed stimuli was significantly associated with lower grey matter volume in the right collateral sulcus, in a region lying between the fusiform and lingual gyri. Detailed error analysis also revealed that similarity between the error response and the averaged target and flanker stimuli (but not individual target or flanker stimuli) was a significant predictor of error rate, more consistent with averaging than substitution accounts of crowding. Our findings suggest that crowding in posterior cortical atrophy can be regarded as a pre-attentive process that uses averaging to regularize the pathologically noisy representation of letter feature position in central vision. These results also help to clarify the cortical localization of feature integration components of crowding. More broadly, we suggest that posterior cortical atrophy provides a neurodegenerative disease model for exploring the basis of crowding. These data have significant implications for patients with, or who will go on to develop, dementia-related visual impairment, in whom acquired excessive crowding likely contributes to deficits in word, object, face and scene perception.
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Affiliation(s)
- Keir X X Yong
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Timothy J Shakespeare
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Dave Cash
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK 2 Centre for Medical Image Computing, University College London, UK
| | - Susie M D Henley
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK 3 University College London Hospitals NHS Foundation Trust, London, UK
| | - Jennifer M Nicholas
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK 4 Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, England, UK
| | - Gerard R Ridgway
- 5 Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK 6 Centre for Functional MRI of the Brain, University of Oxford, Oxford, UK
| | - Hannah L Golden
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Elizabeth K Warrington
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Amelia M Carton
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Diego Kaski
- 7 Division of Brain Sciences, Imperial College London, Charing Cross Hospital, London, UK
| | - Jonathan M Schott
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Jason D Warren
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
| | - Sebastian J Crutch
- 1 Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK
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26
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Abstract
Crowding, the identification difficulty for a target in the presence of nearby flankers, is ubiquitous in spatial vision and is considered a bottleneck of object recognition and visual awareness. Despite its significance, the neural mechanisms of crowding are still unclear. Here, we performed event-related potential and fMRI experiments to measure the cortical interaction between the target and flankers in human subjects. We found that the magnitude of the crowding effect was closely associated with an early suppressive cortical interaction. The cortical suppression was reflected in the earliest event-related potential component (C1), which originated in V1, and in the BOLD signal in V1, but not other higher cortical areas. Intriguingly, spatial attention played a critical role in the manifestation of the suppression. These findings provide direct and converging evidence that attention-dependent V1 suppression contributes to crowding at a very early stage of visual processing.
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27
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Chaney W, Fischer J, Whitney D. The hierarchical sparse selection model of visual crowding. Front Integr Neurosci 2014; 8:73. [PMID: 25309360 PMCID: PMC4174752 DOI: 10.3389/fnint.2014.00073] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Accepted: 08/31/2014] [Indexed: 11/30/2022] Open
Abstract
Because the environment is cluttered, objects rarely appear in isolation. The visual system must therefore attentionally select behaviorally relevant objects from among many irrelevant ones. A limit on our ability to select individual objects is revealed by the phenomenon of visual crowding: an object seen in the periphery, easily recognized in isolation, can become impossible to identify when surrounded by other, similar objects. The neural basis of crowding is hotly debated: while prevailing theories hold that crowded information is irrecoverable - destroyed due to over-integration in early stage visual processing - recent evidence demonstrates otherwise. Crowding can occur between high-level, configural object representations, and crowded objects can contribute with high precision to judgments about the "gist" of a group of objects, even when they are individually unrecognizable. While existing models can account for the basic diagnostic criteria of crowding (e.g., specific critical spacing, spatial anisotropies, and temporal tuning), no present model explains how crowding can operate simultaneously at multiple levels in the visual processing hierarchy, including at the level of whole objects. Here, we present a new model of visual crowding-the hierarchical sparse selection (HSS) model, which accounts for object-level crowding, as well as a number of puzzling findings in the recent literature. Counter to existing theories, we posit that crowding occurs not due to degraded visual representations in the brain, but due to impoverished sampling of visual representations for the sake of perception. The HSS model unifies findings from a disparate array of visual crowding studies and makes testable predictions about how information in crowded scenes can be accessed.
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Affiliation(s)
- Wesley Chaney
- Vision Science Graduate Group, University of California, BerkeleyBerkeley, CA, USA
| | - Jason Fischer
- Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research, Massachusetts Institute of TechnologyCambridge, MA, USA
- Department of Psychology, University of California, BerkeleyBerkeley, CA, USA
| | - David Whitney
- Vision Science Graduate Group, University of California, BerkeleyBerkeley, CA, USA
- Department of Psychology, University of California, BerkeleyBerkeley, CA, USA
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28
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Chicherov V, Plomp G, Herzog MH. Neural correlates of visual crowding. Neuroimage 2014; 93 Pt 1:23-31. [DOI: 10.1016/j.neuroimage.2014.02.021] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 01/18/2014] [Accepted: 02/16/2014] [Indexed: 10/25/2022] Open
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Faivre N, Berthet V, Kouider S. Sustained invisibility through crowding and continuous flash suppression: a comparative review. Front Psychol 2014; 5:475. [PMID: 24904489 PMCID: PMC4034702 DOI: 10.3389/fpsyg.2014.00475] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 05/01/2014] [Indexed: 11/13/2022] Open
Abstract
The study of non-conscious vision benefits from several alternative methods that allow the suppression of an image from awareness. Here, we present and compare two of them that are particularly well-suited for creating sustained periods of invisibility, namely visual crowding and continuous flash suppression (CFS). In visual crowding, a peripheral image surrounded by similar flankers becomes impossible to discriminate. In CFS, an image presented to one eye becomes impossible to detect when rapidly changing patterns are presented to the other eye. After discussing the experimental specificities of each method, we give a comparative overview of the main empirical results derived from them, from the mere analysis of low-level features to the extraction of semantic contents. We conclude by proposing practical guidelines and future directions to obtain more quantitative and systematic measures of non-conscious processes under prolonged stimulation.
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Affiliation(s)
- Nathan Faivre
- Division of Biology, Computation and Neural Systems, California Institute of TechnologyPasadena, CA, USA
- Laboratory of Cognitive Neuroscience, Brain Mind Institute, School of Life Sciences, École Polytechnique Fédérale de LausanneLausanne, Switzerland
| | | | - Sid Kouider
- Laboratoire de Sciences Cognitives et Psycholinguistique, EHESS/CNRS/ENS-DECParis, France
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30
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Joo SJ, Murray SO. Contextual effects in human visual cortex depend on surface structure. J Neurophysiol 2014; 111:1783-91. [PMID: 24523525 DOI: 10.1152/jn.00671.2013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neural responses in early visual cortex depend on stimulus context. One of the most well-established context-dependent effects is orientation-specific surround suppression: the neural response to a stimulus inside the receptive field of a neuron ("target") is suppressed when it is surrounded by iso-oriented compared with orthogonal stimuli ("flankers"). Despite the importance of orientation-specific surround suppression in potentially mediating a number of important perceptual effects, including saliency, contour integration, and orientation discrimination, the underlying neural mechanisms remain unknown. The suppressive signal could be inherited from precortical areas as early as the retina and thalamus, arise from local circuits through horizontal connections, or be fed back from higher visual cortex. Here, we show, using two different methodologies, measurements of scalp-recorded event-related potentials (ERPs) and behavioral contrast adaptation aftereffects in humans, that orientation-specific surround suppression is dependent on the surface structure in an image. When the target and flankers can be grouped on the same surface (independent of their distance), orientation-specific surround suppression occurs. When the target and flankers are on different surfaces (independent of their distance), orientation-specific surround suppression does not occur. Our results demonstrate a surprising role of high-level, global processes such as grouping in determining when contextual effects occur in early visual cortex.
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Affiliation(s)
- Sung Jun Joo
- Department of Psychology, University of Washington, Seattle, Washington
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31
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Abstract
Single-unit recordings demonstrated that the adult mammalian visual cortex is capable of reorganizing after induced retinal lesions. In humans, whether the adult cortex is capable of reorganizing has only been studied using functional magnetic resonance imaging, with equivocal results. Here, we exploited the phenomenon of visual crowding, a major limitation on object recognition, to show that, in humans with long-standing retinal (macular) lesions that afflict the fovea and thus use their peripheral vision exclusively, the signature properties of crowding are distinctly different from those of the normal periphery. Crowding refers to the inability to recognize objects when the object spacing is smaller than the critical spacing. Critical spacing depends only on the retinal location of the object, scales linearly with its distance from the fovea, and is approximately two times larger in the radial than the tangential direction with respect to the fovea, thus demonstrating the signature radial-tangential anisotropy of the crowding zone. Using retinal imaging combined with behavioral measurements, we mapped out the crowding zone at the precise peripheral retinal locations adopted by individuals with macular lesions as the new visual reference loci. At these loci, the critical spacings are substantially smaller along the radial direction than expected based on the normal periphery, resulting in a lower scaling of critical spacing with the eccentricity of the peripheral locus and a loss in the signature radial-tangential anisotropy of the crowding zone. These results imply a fundamental difference in the substrate of cortical processing in object recognition following long-term adaptation to macular lesions.
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32
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Abstract
In peripheral vision, objects in clutter are difficult to identify. The exact cause of this "crowding" effect is unclear. To perceive coherent shapes in clutter, the visual system must integrate certain local features across receptive fields while preventing others from being combined. It is believed that this selective feature integration-segmentation process is impaired in peripheral vision, leading to crowding. We used functional magnetic resonance imaging (fMRI) to investigate the neural origin of crowding. We found that crowding was associated with suppressed fMRI signal as early as V1, regardless of whether attention was directed toward or away from a target stimulus. This suppression in early visual cortex was greatest for stimuli that produced the strongest crowding. In contrast, the pattern of activity was mixed in higher level visual areas, such as the lateral occipital cortex. These results support the view that the deficiency in feature integration and segmentation in peripheral vision is present at the earliest stages of cortical processing.
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Affiliation(s)
| | - A Cyrus Arman
- Neuroscience Graduate Program, Current address: Deallus Group, Los Angeles, CA 90025, USA
| | - Susana T L Chung
- School of Optometry, University of California, Berkeley, CA 94720-2020, USA and
| | - Bosco S Tjan
- Neuroscience Graduate Program, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061, USA
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33
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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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Kosovicheva AA, Sheremata SL, Rokem A, Landau AN, Silver MA. Cholinergic enhancement reduces orientation-specific surround suppression but not visual crowding. Front Behav Neurosci 2012; 6:61. [PMID: 23049505 PMCID: PMC3444757 DOI: 10.3389/fnbeh.2012.00061] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2012] [Accepted: 08/28/2012] [Indexed: 11/13/2022] Open
Abstract
Acetylcholine (ACh) reduces the spatial spread of excitatory fMRI responses in early visual cortex and receptive field size of V1 neurons. We investigated the perceptual consequences of these physiological effects of ACh with surround suppression and crowding, two phenomena that involve spatial interactions between visual field locations. Surround suppression refers to the reduction in perceived stimulus contrast by a high-contrast surround stimulus. For grating stimuli, surround suppression is selective for the relative orientations of the center and surround, suggesting that it results from inhibitory interactions in early visual cortex. Crowding refers to impaired identification of a peripheral stimulus in the presence of flankers and is thought to result from excessive integration of visual features. We increased synaptic ACh levels by administering the cholinesterase inhibitor donepezil to healthy human subjects in a placebo-controlled, double-blind design. In Experiment 1, we measured surround suppression of a central grating using a contrast discrimination task with three conditions: (1) surround grating with the same orientation as the center (parallel), (2) surround orthogonal to the center, or (3) no surround. Contrast discrimination thresholds were higher in the parallel than in the orthogonal condition, demonstrating orientation-specific surround suppression (OSSS). Cholinergic enhancement decreased thresholds only in the parallel condition, thereby reducing OSSS. In Experiment 2, subjects performed a crowding task in which they reported the identity of a peripheral letter flanked by letters on either side. We measured the critical spacing between the targets and flanking letters that allowed reliable identification. Cholinergic enhancement with donepezil had no effect on critical spacing. Our findings suggest that ACh reduces spatial interactions in tasks involving segmentation of visual field locations but that these effects may be limited to early visual cortical processing.
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Affiliation(s)
- Anna A Kosovicheva
- Department of Psychology, University of California, Berkeley Berkeley, CA, USA
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35
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Anderson EJ, Dakin SC, Schwarzkopf DS, Rees G, Greenwood JA. The neural correlates of crowding-induced changes in appearance. Curr Biol 2012; 22:1199-206. [PMID: 22658599 PMCID: PMC3396841 DOI: 10.1016/j.cub.2012.04.063] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 04/10/2012] [Accepted: 04/23/2012] [Indexed: 11/26/2022]
Abstract
Object recognition in the peripheral visual field is limited by crowding: the disruptive influence of nearby clutter. Despite its severity, little is known about the cortical locus of crowding. Here, we examined the neural correlates of crowding by combining event-related fMRI adaptation with a change-detection paradigm. Crowding can change the appearance of objects, such that items become perceptually matched to surrounding objects; we used this change in appearance as a signature of crowding and measured brain activity that correlated with the crowded percept. Observers adapted to a peripheral patch of noise surrounded by four Gabor flankers. When crowded, the noise appears oriented and perceptually indistinguishable from the flankers. Consequently, substitution of the noise for a Gabor identical to the flankers ("change-same") is rarely detected, whereas substitution for an orthogonal Gabor ("change-different") is rarely missed. We predicted that brain areas representing the crowded percept would show repetition suppression in change-same trials but release from adaptation in change-different trials. This predicted pattern was observed throughout cortical visual areas V1-V4, increasing in strength from early to late visual areas. These results depict crowding as a multistage process, involving even the earliest cortical visual areas, with perceptual consequences that are increasingly influenced by later visual areas.
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Affiliation(s)
- Elaine J Anderson
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK.
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36
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Abstract
Background Human object recognition degrades sharply as the target object moves from central vision into peripheral vision. In particular, one's ability to recognize a peripheral target is severely impaired by the presence of flanking objects, a phenomenon known as visual crowding. Recent studies on how visual awareness of flanker existence influences crowding had shown mixed results. More importantly, it is not known whether conscious awareness of the existence of both the target and flankers are necessary for crowding to occur. Methodology/Principal Findings Here we show that crowding persists even when people are completely unaware of the flankers, which are rendered invisible through the continuous flash suppression technique. Contrast threshold for identifying the orientation of a grating pattern was elevated in the flanked condition, even when the subjects reported that they were unaware of the perceptually suppressed flankers. Moreover, we find that orientation-specific adaptation is attenuated by flankers even when both the target and flankers are invisible. Conclusions These findings complement the suggested correlation between crowding and visual awareness. What's more, our results demonstrate that conscious awareness and attention are not prerequisite for crowding.
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Affiliation(s)
- Cristy Ho
- Department of Psychology, The University of Hong Kong, Hong Kong Special Administrative Region, China
| | - Sing-Hang Cheung
- Department of Psychology, The University of Hong Kong, Hong Kong Special Administrative Region, China
- * E-mail:
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37
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Abstract
Crowding occurs when stimuli in the peripheral fields become harder to identify when flanked by other items. This phenomenon has been demonstrated extensively with simple patterns (e.g., Gabors and letters). Here, we characterize crowding for everyday objects. We presented three-item arrays of objects and letters, arranged radially and tangentially in the lower visual field. Observers identified the central target, and we measured contrast energy thresholds as a function of target-to-flanker spacing. Object crowding was similar to letter crowding in spatial extent but was much weaker. The average elevation in threshold contrast energy was in the order of 1 log unit for objects as compared to 2 log units for letters and silhouette objects. Furthermore, we examined whether the exterior and interior features of an object are differentially affected by crowding. We used a circular aperture to present or exclude the object interior. Critical spacings for these aperture and "donut" objects were similar to those of intact objects. Taken together, these findings suggest that crowding between letters and objects are essentially due to the same mechanism, which affects equally the interior and exterior features of an object. However, for objects defined with varying shades of gray, it is much easier to overcome crowding by increasing contrast.
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Affiliation(s)
- Julian M Wallace
- Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061, USA.
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38
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Freeman J, Donner TH, Heeger DJ. Inter-area correlations in the ventral visual pathway reflect feature integration. J Vis 2011; 11:11.4.15. [PMID: 21521832 DOI: 10.1167/11.4.15] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
During object perception, the brain integrates simple features into representations of complex objects. A perceptual phenomenon known as visual crowding selectively interferes with this process. Here, we use crowding to characterize a neural correlate of feature integration. Cortical activity was measured with functional magnetic resonance imaging, simultaneously in multiple areas of the ventral visual pathway (V1-V4 and the visual word form area, VWFA, which responds preferentially to familiar letters), while human subjects viewed crowded and uncrowded letters. Temporal correlations between cortical areas were lower for crowded letters than for uncrowded letters, especially between V1 and VWFA. These differences in correlation were retinotopically specific, and persisted when attention was diverted from the letters. But correlation differences were not evident when we substituted the letters with grating patches that were not crowded under our stimulus conditions. We conclude that inter-area correlations reflect feature integration and are disrupted by crowding. We propose that crowding may perturb the transformations between neural representations along the ventral pathway that underlie the integration of features into objects.
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Affiliation(s)
- Jeremy Freeman
- Center for Neural Science, New York University, New York, NY 10003, USA.
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39
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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: 452] [Impact Index Per Article: 34.8] [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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40
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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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van den Berg R, Roerdink JBTM, Cornelissen FW. A neurophysiologically plausible population code model for feature integration explains visual crowding. PLoS Comput Biol 2010; 6:e1000646. [PMID: 20098499 PMCID: PMC2799670 DOI: 10.1371/journal.pcbi.1000646] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Accepted: 12/15/2009] [Indexed: 11/18/2022] Open
Abstract
An object in the peripheral visual field is more difficult to recognize when surrounded by other objects. This phenomenon is called “crowding”. Crowding places a fundamental constraint on human vision that limits performance on numerous tasks. It has been suggested that crowding results from spatial feature integration necessary for object recognition. However, in the absence of convincing models, this theory has remained controversial. Here, we present a quantitative and physiologically plausible model for spatial integration of orientation signals, based on the principles of population coding. Using simulations, we demonstrate that this model coherently accounts for fundamental properties of crowding, including critical spacing, “compulsory averaging”, and a foveal-peripheral anisotropy. Moreover, we show that the model predicts increased responses to correlated visual stimuli. Altogether, these results suggest that crowding has little immediate bearing on object recognition but is a by-product of a general, elementary integration mechanism in early vision aimed at improving signal quality. Visual crowding refers to the phenomenon that objects become more difficult to recognize when other objects surround them. Recently there has been an explosion of studies on crowding, driven, in part, by the belief that understanding crowding will help to understand a range of visual behaviours, including object recognition, visual search, reading, and texture recognition. Given the long-standing interest in the topic and its relevance for a wide range of research fields, it is quite surprising that after nearly a century of research the mechanisms underlying crowding are still as poorly understood as they are today. A nearly complete lack of quantitative models seems to be one of the main reasons for this. Here, we present a mathematical, biologically motivated model of feature integration at the level of neuron populations. Using simulations, we demonstrate that several fundamental properties of the crowding effect can be explained as the by-product of an integration mechanism that may have a function in contour integration. Altogether, these results help differentiate between earlier theories about both the neural and functional origin of crowding.
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Affiliation(s)
- Ronald van den Berg
- Institute of Mathematics and Computing Science, University of Groningen, Groningen, The Netherlands.
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