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Hussain Z, McGraw PV. Disruption of Positional Encoding at Small Separations in the Amblyopic Periphery. Invest Ophthalmol Vis Sci 2022; 63:15. [PMID: 35446345 PMCID: PMC9034712 DOI: 10.1167/iovs.63.4.15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Positional judgments in amblyopia are impaired more at the center of the visual field than in the periphery. However, the effects of visual field position frequently are confounded with stimulus separation. The purpose of this experiment was to parse the effects of stimulus separation and eccentricity on the positional deficit in amblyopia. Methods Subjects adjusted the positions of stimuli of varying separations on isoeccentric arcs. The task was simultaneous bisection and alignment of broadband, high-contrast, uncrowded targets with reference to central fixation. Ten strabismic amblyopes and five normally sighted controls performed the task dichoptically; a subset of amblyopes performed the task monocularly with the amblyopic eye. Spread (inverse of precision) and bias were measured at multiple visual field locations comprising two to three separation × four eccentricity conditions in each visual field quadrant. Results In normal controls, both spread and bias increased with eccentricity, and spread (but not bias) increased linearly with separation until 7° eccentricity. Strabismic amblyopes showed a different profile: spread and bias were higher at small separations at all eccentricities, such that performance showed a quadratic trend against separation. Thus, at each eccentricity, the difference in performance between groups was largest at the smallest separation. Conclusions These results are consistent with disruptions in Weber mechanisms of positional encoding in strabismic amblyopia, and indicate that binocular stimulation by proximal targets produces a loss of spatial precision well beyond the fovea.
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Affiliation(s)
- Zahra Hussain
- Department of Psychology, American University of Beirut, Lebanon
| | - Paul V McGraw
- School of Psychology, University of Nottingham, United Kingdom
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2
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The neural basis of spatial vision losses in the dysfunctional visual system. Sci Rep 2017; 7:11376. [PMID: 28900225 PMCID: PMC5595843 DOI: 10.1038/s41598-017-11364-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 08/15/2017] [Indexed: 11/14/2022] Open
Abstract
Human vision relies on correct information processing from the eye to various visual areas. Disturbances in the visual perception of simple features are believed to come from low-level network (e.g., V1) disruptions. In the present study, we modelled monocular losses in spatial vision through plausible multiple network modifications in early visual coding. We investigated perceptual deficits in anisometropic amblyopia and used the monocular tilt illusion as a probe of primary visual cortex orientation coding and inhibitory interactions. The psychophysical results showed that orientation misperception was higher in amblyopic eyes (AE) than in the fellow and neurotypical eyes and was correlated with the subject’s AE peak contrast sensitivity. The model fitted to the experimental results allowed to split these observations between different network characteristics by showing that these observations were explained by broader orientation tuning widths in AEs and stronger lateral inhibition in abnormal amblyopic system that had strong contrast sensitivity losses. Through psychophysics measures and computational modelling of V1, our study links multiple perceptual changes with localized modifications in the primary visual cortex.
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3
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Chung STL, Li RW, Levi DM. Learning to identify near-acuity letters, either with or without flankers, results in improved letter size and spacing limits in adults with amblyopia. PLoS One 2012; 7:e35829. [PMID: 22558234 PMCID: PMC3340394 DOI: 10.1371/journal.pone.0035829] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2011] [Accepted: 03/26/2012] [Indexed: 11/18/2022] Open
Abstract
Amblyopia is a developmental abnormality that results in deficits for a wide range of visual tasks, most notably, the reduced ability to see fine details, the loss in contrast sensitivity especially for small objects and the difficulty in seeing objects in clutter (crowding). The primary goal of this study was to evaluate whether crowding can be ameliorated in adults with amblyopia through perceptual learning using a flanked letter identification task that was designed to reduce crowding, and if so, whether the improvements transfer to untrained visual functions: visual acuity, contrast sensitivity and the size of visual span (the amount of information obtained in one fixation). To evaluate whether the improvements following this training task were specific to training with flankers, we also trained another group of adult observers with amblyopia using a single letter identification task that was designed to improve letter contrast sensitivity, not crowding. Following 10,000 trials of training, both groups of observers showed improvements in the respective training task. The improvements generalized to improved visual acuity, letter contrast sensitivity, size of the visual span, and reduced crowding. The magnitude of the improvement for each of these measurements was similar in the two training groups. Perceptual learning regimens aimed at reducing crowding or improving letter contrast sensitivity are both effective in improving visual acuity, contrast sensitivity for near-acuity objects and reducing the crowding effect, and could be useful as a clinical treatment for amblyopia.
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Affiliation(s)
- Susana T L Chung
- School of Optometry, University of California, Berkeley, California, United States of America.
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4
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Sheth KN, Walker BM, Modestino EJ, Miki A, Terhune KP, Francis EL, Haselgrove JC, Liu GT. Neural Correlate of Vernier Acuity Tasks Assessed by Functional MRI (fMRI). Curr Eye Res 2009; 32:717-28. [PMID: 17852197 DOI: 10.1080/02713680701477815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Vernier acuity refers to the ability to discern a small offset within a line. However, while Vernier acuity has been extensively studied psychophysically, its neural correlates are uncertain. Based upon previous psychophysical and electrophysiologic data, we hypothesized that extrastriate areas of the brain would be involved in Vernier acuity tasks, so we designed event-related functional MRI (fMRI) paradigms to identify cortical regions of the brain involved in this behavior. Normal subjects identified suprathreshold and subthreshold Vernier offsets. The results suggest a cortical network including frontal, parietal, occipital, and cerebellar regions subserves the observation, processing, interpretation, and acknowledgment of briefly presented Vernier offsets.
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Affiliation(s)
- Kevin N Sheth
- The Children's Hospital of Philadelphia Functional MRI Research Unit and the University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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5
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Chung STL, Li RW, Levi DM. Learning to identify near-threshold luminance-defined and contrast-defined letters in observers with amblyopia. Vision Res 2008; 48:2739-50. [PMID: 18824189 PMCID: PMC2642955 DOI: 10.1016/j.visres.2008.09.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 09/03/2008] [Accepted: 09/08/2008] [Indexed: 11/24/2022]
Abstract
We assessed whether or not the sensitivity for identifying luminance-defined and contrast-defined letters improved with training in a group of amblyopic observers who have passed the critical period of development. In Experiment 1, we tracked the contrast threshold for identifying luminance-defined letters with training in a group of 11 amblyopic observers. Following training, six observers showed a reduction in thresholds, averaging 20%, for identifying luminance-defined letters. This improvement transferred extremely well to the untrained task of identifying contrast-defined letters (average improvement=38%) but did not transfer to an acuity measurement. Seven of the 11 observers were subsequently trained on identifying contrast-defined letters in Experiment 2. Following training, five of these seven observers demonstrated a further improvement, averaging 17%, for identifying contrast-defined letters. This improvement did not transfer to the untrained task of identifying luminance-defined letters. Our findings are consistent with predictions based on the locus of learning for first- and second-order stimuli according to the filter-rectifier-filter model for second-order visual processing.
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Affiliation(s)
- Susana T L Chung
- School of Optometry, University of California, 360 Minor Hall, Berkeley, CA 94720-2020, USA.
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6
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Vedamurthy I, Suttle CM, Alexander J, Asper LJ. Interocular interactions during acuity measurement in children and adults, and in adults with amblyopia. Vision Res 2007; 47:179-88. [PMID: 17126872 DOI: 10.1016/j.visres.2006.08.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2006] [Revised: 05/31/2006] [Accepted: 08/14/2006] [Indexed: 11/25/2022]
Abstract
The binocular interactions that occur during dichoptic and binocular viewing were investigated using a letter acuity task in normally sighted children (age range 6-14 years) and adults, and in adults with anisometropic amblyopia. Our aims were to investigate the nature of binocular interactions that occur in each group, and the extent to which the characteristics of binocular interactions differ across the groups. The non-tested eye was occluded during monocular (baseline) viewing, and was allowed to view a uniform stimulus with fusion lock in dichoptic viewing. In adults and children with normal vision, acuity under dichoptic viewing was unchanged relative to monocular baseline in the dominant eyes, while acuity of the non-dominant eye improved under dichoptic viewing relative to baseline. The magnitude of dichoptic change in the non-dominant eyes was similar in the two normally sighted groups, but the dichoptic advantage was found to decrease with increasing age within the children tested. Binocular acuity was better than monocular acuity in normal subjects, and a decrease in binocular summation with age was noted within the age range of the children tested. In contrast, the amblyopic observers showed no change in acuity with viewing conditions. The results demonstrate development of interocular interactions during childhood, and wide inter-individual variation in pattern of interocular interactions among anisometropic amblyopic adults.
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Affiliation(s)
- Indu Vedamurthy
- School of Optometry and Vision Science, The University of New South Wales, Sydney, NSW, Australia.
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7
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Chung STL, Li RW, Levi DM. Identification of contrast-defined letters benefits from perceptual learning in adults with amblyopia. Vision Res 2006; 46:3853-61. [PMID: 16930666 PMCID: PMC1852540 DOI: 10.1016/j.visres.2006.06.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2006] [Revised: 06/22/2006] [Accepted: 06/23/2006] [Indexed: 10/24/2022]
Abstract
Amblyopes show specific deficits in processing second-order spatial information (e.g. Wong, Levi, & McGraw (2001). Is second-order spatial loss in amblyopia explained by the loss of first-order spatial input? Vision Research, 41, 2951-2960). Recent work suggests there is a significant degree of plasticity in the visual pathway that processes first-order spatial information in adults with amblyopia. In this study, we asked whether or not there is similar plasticity in the ability to process second-order spatial information in adults with amblyopia. Ten adult observers with amblyopia (five strabismic, four anisometropic and one mixed) were trained to identify contrast-defined (second-order) letters using their amblyopic eyes. Before and after training, we determined observers' contrast thresholds for identifying luminance-defined (first-order) and contrast-defined letters, separately for the non-amblyopic and amblyopic eyes. Following training, eight of the 10 observers showed a significant reduction in contrast thresholds for identifying contrast-defined letters with the amblyopic eye. Five of these observers also showed a partial transfer of improvement to their fellow untrained non-amblyopic eye for identifying contrast-defined letters. There was a small but statistically significant transfer to the untrained task of identifying luminance-defined letters in the same trained eye. Similar to first-order spatial tasks, adults with amblyopia benefit from perceptual learning for identifying contrast-defined letters in their amblyopic eyes, suggesting a sizeable degree of plasticity in the visual pathway for processing second-order spatial information.
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Affiliation(s)
- Susana T L Chung
- College of Optometry and Center for Neuro-Engineering and Cognitive Science, University of Houston, Houston, TX, USA.
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8
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Mansouri B, Allen HA, Hess RF, Dakin SC, Ehrt O. Integration of orientation information in amblyopia. Vision Res 2005; 44:2955-69. [PMID: 15380999 DOI: 10.1016/j.visres.2004.06.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2003] [Revised: 03/01/2004] [Indexed: 11/17/2022]
Abstract
A recent report suggests that amblyopes are deficient in processing local orientation at supra-threshold contrasts. To determine whether amblyopes are also poor at integrating local orientation signals, we assessed performance for an orientation integration task in which the orientations of static signals are integrated across space. Our results show that amblyopic visual systems can integrate local static oriented signals with the same level of efficiency as normal visual systems. Although internal noise was slightly elevated, there was no indication that fewer samples were used to achieve optimal performance. This finding suggests normal integration of local orientation signals in amblyopia.
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Affiliation(s)
- Behzad Mansouri
- McGill Vision Research Unit, 687 Pine Avenue West, Rm. H4-14, Montreal, Quebec, Canada H3A 1A1.
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9
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Demanins R, Hess RF. Positional loss in strabismic amblyopia: inter-relationship of alignment threshold, bias, spatial scale and eccentricity. Vision Res 1996; 36:2771-94. [PMID: 8917764 DOI: 10.1016/0042-6989(95)00318-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
In order to understand the spatial loss in strabismic amblyopia and its relationship to the contrast sensitivity deficit, we measured alignment performance for a three element vertical alignment task in which the elements were equi-visible, spatial Gabors. We derived the threshold and bias and compared these for stimuli of different spatial scale and eccentricity. Our results suggest that: (1) the deficits for alignment thresholds and bias are uncorrelated; (2) in the majority of strabismic amblyopes, both deficits are scale invariant; (3) the form of the regional distribution depends on the spatial measure used and the scale at which it is measured; and (4) there is a poor correlation between the deficit for either spatial measure and the contrast sensitivity loss.
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Affiliation(s)
- R Demanins
- McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada
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10
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Abstract
Spatio-temporal interpolation reconstructs the (complete) motion path of objects presented discontinuously, e.g. under stroboscopic illumination or in television. Interpolative vernier stimuli were created by presenting two line segments with a temporal delay instead of a spatial offset. Ten amblyopic patients had to indicate whether the lower segment of the moving target was offset to the left or right relative to the upper segment. For five patients we also measured thresholds for a conventional moving vernier. Five normal subjects were measured with sharply focused and blurred interpolative verniers. At low velocities of interpolative vernier targets, results of amblyopic eyes are inferior to those of normal eyes. However, 9 out of 10 patients perform better using their amblyopic than using their normal eye at high velocities. In control subjects, blurred stimuli yield results similar to those of amblyopic eyes, indicating a similarity between (optical) blur and the mechanisms underlying amblyopia. Thresholds for conventional vernier targets of amblyopic observers, on the other hand, are constant over the whole velocity range for both normal and amblyopic eyes, with a better performance of the normal eye at all velocities. The consequences for models of amblyopia are discussed.
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Affiliation(s)
- M Fahle
- Department of Neuroophthalmology, University Eye Clinic, Tübingen, Germany.
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11
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Treutwein B, Rentschler I, Zetzsche C, Scheidler M, Boergen KP. Amblyopic quasi-blindness for image structure. Vision Res 1996; 36:2211-28. [PMID: 8776487 DOI: 10.1016/0042-6989(95)00312-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Human amblyopes display reduced contrast sensitivities, suffer from perceptual distortion, and their letter acuities are worse than is predicted from grating visibility. We sought the origin of these dysfunctions by measuring normal and amblyopic sensitivities to various forms of well-defined image distortion, namely band-limited phase quantization, phase quantization with additional amplitude modulation, and grey-scale modification. Our results prove the existence of an amblyopic quasi-blindness to image structure, that cannot be explained in terms of contrast detection. We discuss these findings within the computational scheme of image decomposition into local amplitude and local phase values. they are consistent with the assumption of amblyopic eyes beings impaired in processing local phase but having the local amplitude (or "energy", possibly at reduced gain) at their disposal. Phrased in physiological terms, we propose a scheme of complex-cells-only vision in amblyopia. We also provide a demonstration of how amblyopic eyes may see the test stimuli and natural images by generating local amplitude and phase representations at limited phase resolution.
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Affiliation(s)
- B Treutwein
- Institute of Medical Psychology, University of Munich, Germany
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12
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Demanins R, Hess RF. Effect of exposure duration on spatial uncertainty in normal and amblyopic eyes. Vision Res 1996; 36:1189-93. [PMID: 8762722 DOI: 10.1016/0042-6989(95)00181-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Previous studies have found that the spatial uncertainty of amblyopes is critically dependent on temporal factors. These studies claim that the spatial uncertainty is much greater at short exposure durations. We have reassessed the effect of exposure duration on the spatial uncertainty of normal and amblyopic eyes using a task in which we can compensate for the loss in contrast sensitivity which inevitably occurs as exposure duration is shortened. Our task involved a three-element alignment task, where each of the elements were spatial Gabors at two different separations. We ensured that our stimuli were always displayed at a fixed ratio above contrast detection thresholds at each exposure duration. Our results show that for normal subjects, for well separated equivisible stimuli, there is only a weak effect of exposure duration. A similar dependence is found for the dominant and amblyopic eyes of a group of strabismic amblyopes. Dominant eyes of strabismic amblyopes show increased spatial uncertainty compared with normal subjects. Amblyopic eyes of strabismic amblyopes show increased spatial uncertainty compared with their dominant fellow eye which is invariant with exposure duration. Some subjects show a larger positional deficit at short durations when the stimuli are almost abutting.
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Affiliation(s)
- R Demanins
- Department of Ophthalmology, Montreal, Quebec, Canada
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13
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Mullen KT, Sankeralli MJ, Hess RF. Color and luminance vision in human amblyopia: shifts in isoluminance, contrast sensitivity losses, and positional deficits. Vision Res 1996; 36:645-53. [PMID: 8762296 DOI: 10.1016/0042-6989(95)00159-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The deficits for contrast detection and positional accuracy were compared for chromatic and luminance mechanisms within a group of strabismic and anisometropic amblyopes. We found that the isoluminant point was shifted towards red in the amblyopic compared to the fellow normal eye. This was not accounted for by eccentric fixation by the amblyopic eye. Contrast sensitivity deficits were similar for luminance and color stimuli in normal and amblyopic visual systems. In the majority of our amblyopic subjects, however, the deficits in positional acuity were greater for the chromatic than the luminance stimuli.
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Affiliation(s)
- K T Mullen
- Department of Ophthalmology, McGill University, Montreal, Canada.
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14
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Hess RF, Field DJ. Is the spatial deficit in strabismic amblyopia due to loss of cells or an uncalibrated disarray of cells? Vision Res 1994; 34:3397-406. [PMID: 7863622 DOI: 10.1016/0042-6989(94)90073-6] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We examine two competing explanations for the spatial localization deficit in human strabismic amblyopia, namely neural undersampling and uncalibrated neural disarray. An undersampling hypothesis would predict an associated deficit for contrast discrimination for which we find no evidence in strabismic amblyopia. A neural disarray hypothesis would predict an associated deficit in the degree to which stimuli appear spatially distorted. We find evidence for such a deficit in strabismic amblyopia. We propose that the spatial deficit in strabismic amblyopia is due to a filter-based distortion which is unable to be re-calibrated by higher visual centres.
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Affiliation(s)
- R F Hess
- McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada
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15
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Swanson WH. Analysis of Rayleigh match data with psychometric functions. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 1993; 10:1807-1817. [PMID: 8350163 DOI: 10.1364/josaa.10.001807] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Color matches have been used for a variety of purposes, yet the psychometric properties of color-matching data have not been thoroughly investigated. A method is given for generating psychometric functions for the two ends of the color-matching range by use of a perceptual dimension for stimulus magnitude based on ratios of cone quantal catches. The analysis was applied to Rayleigh match data gathered from 250 naïve observers with an automated protocol. Slopes of the psychometric functions were significantly shallower for anomalous trichromats than for normal trichromats, consistent with the assumption that stimulus magnitude is based on ratios of cone quantal catches. These results indicate that the tester's criterion for response consistency can strongly affect Rayleigh match widths. The analysis may also be useful for other perceptual tasks, such as contrast matching and spatial alignment.
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Affiliation(s)
- W H Swanson
- Retina Foundation of the Southwest, Dallas, Texas 75231
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16
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Abstract
We used Gaussian blurred stimuli to explore the effect of blur on three tasks: (i) 2-line resolution; (ii) line detection; and (iii) spatial interval discrimination, in observers with amblyopia due to anisometropia, strabismus, or both. The results of our experiments can be summarized as follows. (i) 2-Line resolution: in normal foveal vision, thresholds for unblurred stimuli are approx. 0.5 min arc in the fovea. When the standard deviation (sigma) of the stimulus blur is less than 0.5 min, it has little effect upon 2-line resolution; however, thresholds are degraded when the stimulus blur, sigma, exceeds 0.5 min. We operationally define this transition point, as the equivalent intrinsic blur, or Bi. When the stimulus blur, sigma, is greater than Bi, then the resolution threshold is approximately equal to sigma. In all of the amblyopic eyes, 2-line resolution thresholds for unblurred stimuli were elevated, and the equivalent intrinsic blur was much larger. When the stimulus blur exceeds the equivalent intrinsic blur, resolution thresholds were similar in amblyopic and nonamblyopic eyes. (ii) Line detection: in both normal and amblyopic eyes, when the stimulus blur, sigma, is less than Bi, then the line detection threshold is approximately inversely proportional to sigma; i.e. (it obeys Ricco's law). When sigma is greater than Bi, the equivalent intrinsic blur, then the detection threshold is approximately a fixed contrast. All of the amblyopic eyes showed markedly elevated thresholds for detecting thin lines, but normal or near normal thresholds for detecting very blurred lines. Consequently, Ricco's diameter is larger in amblyopic than in normal eyes. (iii) Spatial interval discrimination: thresholds are proportional to the separation of the lines (i.e. Weber's law). At the optimal separation, spatial interval discrimination thresholds represent a "hyperacuity" (i.e. they are smaller than the resolution threshold). For unblurred lines, the optimal separation is approx. 2-3 times Bi. In the normal fovea, and in the amblyopic eyes of anisometropic amblyopes the optimal spatial interval discrimination threshold is about one-fifth of the resolution threshold (i.e. a hyperacuity); and over a wide range of separations, spatial interval discrimination thresholds begin to rise when the stimulus blur exceeds about one-third of the separation between the lines as long as the contrast is sufficiently high. In contrast, in strabismic amblyopes, like the normal periphery, the optimal spatial interval discrimination thresholds are worse (higher) than would be expected based upon the resolution limit of the strabismic amblyopic eye.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- D M Levi
- University of Houston, College of Optometry, TX 77004
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17
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Hilz R, Rentschler I, Baier M. Segregation of color and form. Intact spatial wavelength discrimination in strabismic amblyopia. THE SCIENCE OF NATURE - NATURWISSENSCHAFTEN 1989; 76:479-80. [PMID: 2586630 DOI: 10.1007/bf00366230] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- R Hilz
- Institut für Medizinische Psychologie der Universität, München
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18
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Abstract
Anisometropic amblyopes were found to have a reduced sensitivity for shape discrimination. The introduction of positional jitter in the elements of the display had a profound effect on the performance of the normal eye, but not on that of the amblyopic eye. On the other hand the introduction of gaussian blur affects the performance of both eyes to the same degree. We conclude that raised spatial uncertainty due to metrical scrambling is a suitable model for anisometropic amblyopia.
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Affiliation(s)
- R J Watt
- MRC Applied Psychology Unit, Cambridge, England
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19
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Abstract
Three experiments were performed to examine positional acuity and the role of spatial sampling in central, peripheral and amblyopic vision. In the first experiment, 3-line bisection acuity was compared to grating acuity. In normal foveal vision bisection acuity represents a hyperacuity. In anisometropic amblyopes, bisection acuity is reduced in rough proportion to their grating acuity. In strabismic amblyopes, and in the normal periphery, bisection acuity is reduced to a greater extent than grating acuity. This result implies that reduced contrast sensitivity of the spatial filters is not sufficient to account for the increased positional uncertainty found in peripheral vision and in strabismic amblyopia. In order to test the hypothesis that the high degree of positional uncertainty evident in these visual systems is a consequence of sparse spatial sampling, bisection thresholds and width discrimination thresholds were measured with stimuli comprised of discrete samples. The results showed that normal foveal vision and the vision of anisometropic amblyopes show little benefit from adding discrete samples to the stimulus. In contrast, the normal periphery, and the central field of strabismic amblyopes demonstrate marked positional uncertainty which can be efficiently reduced in proportion to the square root of the number of samples (up to about 10) comprising the stimulus in the direction orthogonal to the discrimination cue. In aggregate the results suggest that anisometropic and strabismic amblyopia are fundamentally different. The positional uncertainty in anisometropic amblyopia is consistent with the reduced sensitivity of the spatial filters. The data of the normal periphery and of the central field of strabismic amblyopes suggest that the cortical sampling grain imposes a fundamental limit upon their positional acuity.
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Affiliation(s)
- D M Levi
- University of Houston, College of Optometry, Houston, TX 77004
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