Research Topics
Species | LIMITING FACTORS IN NORMAL AND AMBLYOPIC SPATIAL VISIONSummaryPrincipal Investigator: DENNIS MICHAEL LEVI Affiliation: University of California Country: USA Abstract: Our long-range objective is to understand the mechanisms that limit spatial vision in humans with amblyopia. We propose to test a number of specific hypotheses and predictions about these factors, and to assess the limits and mechanisms of neural plasticity in adults and children with amblyopia. Aim 1. Crowding. Feature binding and positional uncertainty in amblyopic and peripheral vision: We hypothesize that both crowding and anomalous feature binding in peripheral and amblyopic vision can be explained by limits imposed by early processes in cortical area V1. We propose a series of experiments, using novel methods and modeling, to answer the following questions: i) Do feature binding and crowding share the same spatial properties? ii) Is there mis-mapping of retinal location to perceived visual space in amblyopia, and is this the result of mis-wiring within feature maps or mis-registration between them? An Adaptive Optics Scanning Laser Ophthalmoscope allows us to deliver point stimuli to precisely identifiable single cones in the retina, and evaluate their perceived location iii) Does crowding impose a critical limit on reading in peripheral and amblyopic vision? Aim 2. Deficits exist at multiple levels in the amblyopic visual system: Recent results lead to the hypothesis that although dysfunction within the amblyopic visual system first occurs in area V1, it is amplified downstream. We will test the prediction that amblyopes will show deficits in "higher level" tasks that cannot be explained by low level considerations: i) second-order processing, ii) contour integration, and iii) temporal, spatial and/or capacity limits of attention. Aim 3. Neural Plasticity in normal and amblyopic vision: There is a surprising degree of neural plasticity in both normal and amblyopic adults as evidenced by perceptual learning, i) We will test the hypothesis that perceptual learning occurs at a high level and reflects the brain learning to attend to and use the most reliable information for the task, ii) Assess the time course, limits and mechanisms of plasticity in adults and young children with amblyopia undergoing both perceptual learning and clinical treatment. We predict that improvement following the successful treatment of amblyopia involves the same mechanisms that improve normal vision following perceptual learning, iii) We will test the prediction that the successful effects of treatment or perceptual learning in amblyopia will lead to increased foveal activation in the visual cortex, as evidenced by alterations in functional MRI. Funding Period: 1976-05-01 - 2011-11-30 more information: NIH RePORT Top Publications
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Stochastic model for detection of signals in noiseStanley A Klein
School of Optometry, University of California, Berkeley, Berkeley, California 94720, USA
J Opt Soc Am A Opt Image Sci Vis 26:B110-26. 2009..In addition, we modify present models to better handle detection of signals with both noise and pedestal backgrounds...
Temporal dynamics of directional selectivity in human visionPeter Neri
School of Optometry and Helen Wills Neuroscience Institute, University of California at Berkeley, Berkeley, CA 94720, USA
J Vis 8:22.1-11. 2008..We successfully modeled this bimodal behavior using a simple circuit where each directional filter normalizes its own output, with the normalizing signal delayed by approximately 100 ms...- Crowding between first- and second-order letters in amblyopiaSusana T L Chung
College of Optometry and Center for Neuro Engineering and Cognitive Science, University of Houston, Houston, TX, USA
Vision Res 48:788-98. 2008..Our findings are consistent with the hypothesis that crowding results from an abnormal integration of target and flankers beyond the stage of feature detection, which takes place over a large distance in amblyopic vision... - Crowding--an essential bottleneck for object recognition: a mini-reviewDennis M Levi
University of California at Berkeley, School of Optometry and The Helen Wills Neuroscience Institute, Berkeley, CA 94720 2020, USA
Vision Res 48:635-54. 2008..A full understanding of crowding may allow us to understand this bottleneck to object recognition and the rules that govern the integration of features into objects... - Amblyopic reading is crowdedDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA 94720 2020, USA
J Vis 7:21.1-17. 2007..The uncrowded-span model of normal reading fits the amblyopic results well, with a roughly fivefold increase in the critical spacing at fixation. Thus, the entire amblyopic reading deficit is accounted for by crowding... - Crowding and surround suppression: not to be confusedYury Petrov
Psychology Department, Northeastern University, Boston, MA 02115, USA
J Vis 7:12.1-9. 2007..Surround suppression apparently dominates at low contrasts, which would explain some of the reported similarities between the two phenomena... - Crowding between first- and second-order letter stimuli in normal foveal and peripheral visionSusana T L Chung
College of Optometry and Center for Neuro Engineering and Cognitive Science, University of Houston, Houston, TX, USA
J Vis 7:10.1-13. 2007..Our finding of substantial interaction between first- and second-order stimuli suggests that the processing of these stimuli is not independent at the stage of processing at which crowding occurs... - Crowding is directed to the fovea and preserves only feature contrastYury Petrov
Psychology Department, Northeastern University, Boston, MA 02115, USA
J Vis 7:8.1-9. 2007..Thus, crowding appears to spare only the most salient peripheral information, which supports the hypothesis that crowding is caused by limitations of attentional resolution... - The wallpaper illusion explainedSuzanne P McKee
Smith Kettlewell Eye Research Institute, San Francisco, CA 94115, USA
J Vis 7:10.1-11. 2007..We speculate that access to the most sensitive V1 neurons depends on the extrastriate processes that determine perceived depth--in this case, second-order envelope mechanisms... 
Extended perceptual learning results in substantial recovery of positional acuity and visual acuity in juvenile amblyopiaRoger W Li
School of Optometry, University of California Berkeley, Berkeley, CA 94720 2020, USA
Invest Ophthalmol Vis Sci 48:5046-51. 2007..The present study was conducted to determine whether extended training is necessary for optimal treatment of amblyopia...- Attentional blinks as errors in temporal bindingAriella V Popple
School of Optometry and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720 2020, USA
Vision Res 47:2973-81. 2007..We suggest that this disruption occurs within a certain time (approximately 0.5 s) after the first target, during which period salient distractors are as likely as the second target to enter working memory... - Integration across Time Determines Path Deviation Discrimination for Moving ObjectsDavid Whitaker
Department of Optometry, University of Bradford, Bradford, United Kingdom
PLoS ONE 3:e1930. 2008..In this study we characterize our ability to judge changes in the direction of motion of objects-a common task which can allow us either to intercept moving objects, or else avoid them if they pose a threat... - What limits performance in the amblyopic visual system: seeing signals in noise with an amblyopic brainDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA 94720 2020, USA
J Vis 8:1.1-23. 2008..This loss is more or less independent of external noise contrast over a log unit range of external noise... - Amblyopia masks the scale invariance of normal central visionDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA, USA
J Vis 9:22.1-11. 2009.... - The time course of contrast masking reveals two distinct mechanisms of human surround suppressionYury Petrov
Department of Psychology, Northeastern University, Boston, MA, USA
J Vis 9:21.1-11. 2009.... - Perceptual learning as a potential treatment for amblyopia: a mini-reviewDennis M Levi
School of Optometry and The Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720 2020, United States
Vision Res 49:2535-49. 2009..The success of PL raises the question of whether it should become a standard part of the armamentarium for the clinical treatment of amblyopia, and suggests several important principles for effective perceptual learning in amblyopia... - The attentional blink in amblyopiaAriella V Popple
School of Optometry and Helen Wills Neuroscience Institute, University of California at Berkeley, Berkeley, CA, USA
J Vis 8:12.1-9. 2008..These findings highlight the role of early (monocular) visual processes in modulating the attentional blink, as well as the role of attention in amblyopic visual deficits... - Prolonged perceptual learning of positional acuity in adult amblyopia: perceptual template retuning dynamicsRoger W Li
School of Optometry and The Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California 94720 2020, USA
J Neurosci 28:14223-9. 2008..These results show that the mature amblyopic brain is surprisingly malleable, and point to more intensive treatment methods for amblyopia... - Complete transfer of perceptual learning across retinal locations enabled by double trainingLu Qi Xiao
State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, Beijing 100875, China
Curr Biol 18:1922-6. 2008.... - Improving the performance of the amblyopic visual systemDennis M Levi
School of Optometry and The Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720 2020, USA
Philos Trans R Soc Lond B Biol Sci 364:399-407. 2009..These findings, along with the results of new clinical trials, suggest that it might be time to reconsider our notions about neural plasticity in amblyopia... - Evidence for joint encoding of motion and disparity in human visual perceptionPeter Neri
Institute of Medical Sciences, University of Aberdeen, Aberdeen, UK
J Neurophysiol 100:3117-33. 2008..Both components are involved in the perception of stimuli containing motion and disparity information in line with the known existence of corresponding neuronal subpopulations in visual cortex... - Learning to identify near-threshold luminance-defined and contrast-defined letters in observers with amblyopiaSusana T L Chung
School of Optometry, University of California, 360 Minor Hall, Berkeley, CA 94720 2020, USA
Vision Res 48:2739-50. 2008..Our findings are consistent with predictions based on the locus of learning for first- and second-order stimuli according to the filter-rectifier-filter model for second-order visual processing... - On the effective number of tracked trajectories in amblyopic human visionSrimant P Tripathy
Division of Optometry, School of Life Sciences, University of Bradford, Bradford, United Kingdom
J Vis 8:8.1-22. 2008..A comparison with data previously published for normal eyes failed to reveal any deficit in the effective number of trajectories tracked by the non-amblyopic eyes of amblyopic observers for the current task... - The response of the amblyopic visual system to noiseDennis M Levi
University of California, Berkeley, School of Optometry and The Helen Wills Neuroscience Institute, Berkeley, CA 94720 2020, USA
Vision Res 47:2531-42. 2007..However, for the discrimination of suprathreshold white noise contrast, there is surprisingly little additional deficit, after accounting for the visibility of the noise... - Collinearity improves alignment in amblyopia as well as in normal visionAriella V Popple
Optometry, UC Berkeley, CA 94720 2020, USA
Vision Res 47:1968-73. 2007.... - Learning to identify contrast-defined letters in peripheral visionSusana T L Chung
College of Optometry and Center for Neuro Engineering and Cognitive Science, University of Houston, Houston, TX, USA
Vision Res 46:1038-47. 2006..The complete interocular transfer, and the retinotopic (retinal location) and size specificity of the learning effect are consistent with the properties of neurons in early visual area V2... - Perceptual learning improves visual performance in juvenile amblyopiaRoger W Li
School of Optometry and Helen Wills Neuroscience Institute, University of California-Berkeley, Berkeley, CA 94720-2020, USA
Invest Ophthalmol Vis Sci 46:3161-8. 2005..The improvement can be parsed into two important factors: decreased equivalent input noise and increased efficiency. Perceptual learning techniques may add an effective new method to the armamentarium of amblyopia treatments... - Spatial interactions reveal inhibitory cortical networks in human amblyopiaErwin H Wong
School of Optometry, University of California, Berkeley, CA 94720, USA
Vision Res 45:2810-9. 2005..Furthermore, strabismic observers with no loss of visual acuity show a similar pattern of detection suppression. We speculate that amblyopia results in predominantly inhibitory cortical interactions between second-order neurons... - Second-order spatial summation in amblyopiaErwin H Wong
School of Optometry, University of California, Berkeley, CA 94720, USA
Vision Res 45:2799-809. 2005..We conclude that the pooling of second-order contrast across visual space is unaffected by amblyopia... - What is the signal in noise?Dennis M Levi
University of California, Berkeley, School of Optometry and The Helen Wills Neuroscience Institute, Berkeley, CA 94720 2020, USA
Vision Res 45:1835-46. 2005..Surprisingly, we found that the human template is "adaptive"-- its shape depends on the spatial frequency band of the noise-suggesting that sensitivity to spatial noise is not simply determined via passive filtering... - "Phase capture" in amblyopia: the influence function for sampled shapeDennis M Levi
University of California, Berkeley, School of Optometry and Helen Wills Neuroscience Institute, Berkeley, CA 94720 2020, USA
Vision Res 45:1793-805. 2005..We speculate that this may be a consequence of abnormal "crowding" of the inner patches by the outer ones... - Location coding by the human visual system: multiple topological adaptations in a case of strabismic amblyopiaAriella V Popple
School of Optometry, University of California at Berkeley, Berkeley, CA 94720 2020, USA
Perception 34:87-107. 2005..Instead, the observed behavior suggests that multiple adaptations of the underlying cortical topology are possible simultaneously in different parts of the visual field... - Perceptual learning in adults with amblyopia: a reevaluation of critical periods in human visionDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720 2020, USA
Dev Psychobiol 46:222-32. 2005..It is hypothesized that these same mechanisms account for at least some of the improvement that occurs in the treatment of amblyopia... - Learning letter identification in peripheral visionSusana T L Chung
College of Optometry and Center for Neuro Engineering and Cognitive Science, University of Houston, 505 J Davis Armistead Bldg, Houston, TX 77204 2020, USA
Vision Res 45:1399-412. 2005..Results from both the PTM analysis and the double-pass experiment imply that the stimulus-dependent component of the internal noise does not change with learning... - The perception of spatial order at a glanceAriella V Popple
School of Optometry and Helen Wills Neuroscience Institute, Berkeley, University of California at Berkeley, Gayley Road, Berkeley, CA 94720 2020, USA
Vision Res 45:1085-90. 2005..Regardless of spacing and set-size, confusions between neighbors were unexpectedly frequent, suggesting there is positional as well as object uncertainty... - Two sources of error in pop-out localizationAriella V Popple
School of Optometry, Helen Wills Neuroscience Institute, UC Berkeley, CA 94720 2020, USA
Vision Res 46:293-8. 2006.... - Spatial resolution for feature binding is impaired in peripheral and amblyopic visionPeter Neri
School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720 2020, USA
J Neurophysiol 96:142-53. 2006..Our results in persons with amblyopia indicate that the ability of the fovea to compensate for this poor co-registration is consolidated by visual experience during postnatal development... - Image segregation in strabismic amblyopiaDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720 2020, USA
Vision Res 47:1833-8. 2007..I therefore conclude that these deficits are not a consequence of abnormal segregation of figure from background... - Sensitivity to biological motion drops by approximately 1/2 log-unit with inversion, and is unaffected by amblyopiaPeter Neri
School of Optometry, University of California at Berkeley, Berkeley, CA 94720 2020, USA
Vision Res 47:1209-14. 2007..Our data provide a quantitative estimate of the inversion effect for biological motion, and demonstrate that higher-level processing in the motion hierarchy is not affected by amblyopia... - Global contour processing in amblyopiaDennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720 2020, USA
Vision Res 47:512-24. 2007..The residual deficits reported here cannot be simply ascribed to reduced visibility or increased positional uncertainty, and we therefore conclude that these are genuine deficits in global contour segregation and integration... - Is the ability to identify deviations in multiple trajectories compromised by amblyopia?Dennis M Levi
School of Optometry and Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, CA 94720 2020, USA
J Vis 6:1367-79. 2006..We conclude that while amblyopia disrupts static angle discrimination, amblyopic dynamic deviation detection thresholds are normal or very nearly so... - Temporal dynamics of figure-ground segregation in human visionPeter Neri
School of Optometry, University of California at Berkeley, Berkeley, CA, USA
J Neurophysiol 97:951-7. 2007..Figure enhancement within this narrow temporal window was transient rather than sustained as may be expected from measurements in single neurons. These psychophysical results prompt and guide further electrophysiological studies... - Meaningful interactions can enhance visual discrimination of human agentsPeter Neri
School of Optometry, University of California at Berkeley, Berkeley, California 94720 2020, USA
Nat Neurosci 9:1186-92. 2006..Our results demonstrate that action understanding has a pervasive impact on the human ability to extract visual information from the actions of other humans, providing quantitative evidence of its significance for sensory performance... - Identification of contrast-defined letters benefits from perceptual learning in adults with amblyopiaSusana T L Chung
College of Optometry and Center for Neuro Engineering and Cognitive Science, University of Houston, Houston, TX, USA
Vision Res 46:3853-61. 2006.... - The receptive field and internal noise for position acuity change with feature separationRoger W Li
School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA
J Vis 6:311-21. 2006..Although systematic internal noise is thought to be one of the important components limiting detection thresholds, we found that systematic noise is negligible in our position task... - Receptive versus perceptive fields from the reverse-correlation viewpointPeter Neri
School of Optometry, University of California, 360 Minor Hall, Berkeley, CA 94720 2020, USA
Vision Res 46:2465-74. 2006.... - Visual processing in amblyopia: human studiesDennis M Levi
University of California at Berkeley, School of Optometry, Berkeley, CA 94720, USA
Strabismus 14:11-9. 2006..3) There appears to be substantial neural plasticity in the amblyopic brain beyond the "critical period.".. - "Crowding" in normal and amblyopic vision assessed with Gaussian and Gabor C'sSrividhya Hariharan
College of Optometry, University of Houston, Houston, TX 77204-6052, USA
Vision Res 45:617-33. 2005..Instead we suggest that crowding in amblyopic and peripheral vision is a result of extended pooling at a stage following the stage of feature detection...