Distortions in two-dimensional visual space perception in strabismic observers

doi:10.1016/0042-6989(93)90188-3

Vision Research

Volume 33, Issues 5–6, March–April 1993, Pages 677-690

https://doi.org/10.1016/0042-6989(93)90188-3 Get rights and content

Abstract

Amblyopic subjects were asked to memorize circles of different radii (2, 4 and 6°), and then to reconstruct them monocularly with each eye, point by point (12 points per circle). The resulting two-dimensional maps of visual space showed considerable distortions, including expansion, shrinkage and torsion of specific regions of the visual field of the amblyopic eye, but not the normal eye. Based on the differences between the two eyes, we computed complex two-dimensional patterns (gratings, checkerboards, optotypes, written text, natural scenes) as “seen” monocularly with the amblyopic eye. These reconstructed patterns were then compared with drawings of the same patterns observed through the amblyopic eyes of the same subjects. The reconstructed patterns only partially reflected the actual perception for the amblyopic eyes. The compensation of complex, globally-extended scenes in comparison to the distortions obtained by local, punctate settings probably reflects cooperative interactions occurring at higher brain levels.

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People with amblyopia demonstrate a reduced ability to judge depth using stereopsis. Our understanding of this deficit is limited, as standard clinical stereo tests may not be suited to give a quantitative account of the residual stereo ability in amblyopia. In this study we used a stereo test designed specifically for that purpose. Participants identified the location of a disparity-defined odd-one-out target within a random-dot display. We tested 29 amblyopic (3 strabismic, 17 anisometropic, 9 mixed) participants and 17 control participants. We obtained stereoacuity thresholds from 59% of our amblyopic participants. There was a factor of two difference between the median stereoacuity of our amblyopic (103 arcsec) and control (56 arcsec) groups. We used the equivalent noise method to evaluate the role of equivalent internal noise and processing efficiency in amblyopic stereopsis. Using the linear amplifier model (LAM), we determined the threshold difference was due to a greater equivalent internal noise in the amblyopic group (238 vs 135 arcsec), with no significant difference in processing efficiency. A multiple linear regression determined 56% of the stereoacuity variance within the amblyopic group was predicted by the two LAM parameters, with equivalent internal noise predicting 46% alone. Analysis of control group data aligned with our previous work, finding that trade-offs between equivalent internal noise and efficiency play a greater role. Our results allow a better understanding of what is limiting amblyopic performance in our task. We find this to be a reduced quality of disparity signals in the input to the task-specific processing.
Two cortical deficits underlie amblyopia: A multifocal fMRI analysis
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Citation Excerpt :
It is also accepted that the deficit in amblyopia must extend beyond V1 (Barnes et al., 2001; Kiorpes et al., 1998; Kiorpes and McKee, 1999) and also involve more than just contrast coding (Gingras et al., 2005a; Hess and Field, 1994; Tao et al., 2014) because, behaviorally, there are a host of visual sensitivities affected in addition to contrast (Aaen-Stockdale et al., 2007; Bedell and Flom, 1981; Levi and Klein, 1982; Mansouri et al., 2005; Sharma et al., 2000; Simmers et al., 2003). Prime amongst these is a deficit involving global spatial distortions (Hess et al., 1978; Sireteanu et al., 1993) and anomalous coding of local position (Bedell and Flom, 1981; Levi et al., 1985). This has now been demonstrated using a host of different approaches (Bedell and Flom, 1983; Bedell et al., 1985; Hess et al., 1978; Hess and Holliday, 1992; Levi and Klein, 1983; Levi et al., 1985; Mansouri et al., 2009; Sireteanu et al., 1993) and shown to be separate from the contrast coding abnormality (Hess and Field, 1994; Hess and Holliday, 1992) prompting a redefinition of the condition in terms of Tarachopia (distorted sight) rather than Amblyopia (blunt sight) (Hess, 1982).
Amblyopia is a relatively common (incidence 3%) developmental disorder in which there is loss of vision as a consequence of a disruption to normal visual development. Although the deficit is monocular and known to be of cortical origin, the nature of the processing deficit is controversial. Human behavioral studies have identified two main deficits — a loss of contrast sensitivity and perceived spatial distortions. Here we use a multifocal fMRI approach to ascertain, in a group of anisometropic amblyopes, whether these two deficits have a single common cause or whether they are the result of two underlying independent cortical disorders. We found that fMRI magnitudes were attenuated in amblyopic eye stimulation, and that there was poor fidelity for co-localization of the activity clusters between the amblyopic and fellow-fixing eye stimulation. These effects varied across eccentricities and correlate with the degree of amblyopia but not with one another, suggesting two independent cortical deficits: a reduced responsiveness as well as reduced fidelity of spatial representation. These deficits are independent of eccentricity within the central field and consistent across early cortical visual areas.
Differential effects of high-frequency transcranial random noise stimulation (hf-tRNS) on contrast sensitivity and visual acuity when combined with a short perceptual training in adults with amblyopia
2018, Neuropsychologia
Citation Excerpt :
The most common aetiologies of amblyopia are untreated strabismus, which consists of a misalignment of the eyes, anisometropia, which is an unequal refractive error between the two eyes, or both strabismus and anisometropia (Giaschi et al., 2015). Spatial vision abnormalities in amblyopia include reductions in visual acuity (VA), contrast sensitivity function (CSF) (Hess and Howell, 1977), and Vernier acuity as well as spatial distortion (Sireteanu et al., 1993), abnormal spatial interactions (Polat et al., 1997), impaired contour detection (Kovács et al., 2000), deficiencies in stereopsis (Wallace et al., 2011), and more generally, global processing of form and motion (Aaen-Stockdale and Hess, 2008; Constantinescu et al., 2005; Ho et al., 2005; Husk et al., 2012; Simmers et al., 2003, 2005, 2006; Simmers and Bex, 2004). Despite some early indications that the retina may be the primary site of amblyopia (Hess, 2001), the current unanimous opinion is that the primary site of neural loss in amblyopia is found at the level of the primary visual cortex (V1) and it is due to an atypical pattern of functional connectivity among neurones selective for orientation and spatial frequency (Polat, 1999; Polat et al., 1997).
Amblyopia is a neuro-developmental disorder characterised by several functional impairments in spatial vision even with the best optical correction. There is evidence that extensive perceptual training can improve visual acuity (VA) and contrast sensitivity (CS) in adults with amblyopia. In the present study, we assessed the efficacy of a recently developed neuro-modulatory technique (i.e., high-frequency transcranial random noise stimulation; hf-tRNS) combined with a short perceptual training in adults with amblyopia. One group of ten participants underwent a short (8 sessions) monocular training in a contrast detection task with concurrent hf-tRNS, whereas another group of ten participants underwent the same training protocol but with Sham stimulation (control group). The training consisted of a two-interval forced choice (2IFC) contrast detection task in which participants had to detect the presence of a central Gabor patch flanked by two high-contrast collinear Gabors (lateral masking). The results showed a significant and similar improvement of CS for both groups, suggesting that hf-tRNS is not crucial for the improvement of CS. However, for VA, a significant improvement was only observed in the hf-tRNS group with a mean VA improvement of 0.19 LogMAR in the amblyopic eye. Most notably, this improvement was achieved after eight training sessions. The results are discussed in terms of the influence of hf-tRNS on short-term neural plasticity.
Occlusion therapy improves phase-alignment of the cortical response in amblyopia
2015, Vision Research
Citation Excerpt :
For each of these disorders a suboptimal retinal image in one eye, interocular disparity of visual inputs, or both limit the postnatal visual development of one eye resulting in decreased visual acuity. Additional visual deficits include reduced contrast sensitivity, reduced Vernier acuity, temporal instability, motion, and global motion deficits, and abnormal contour interactions (Altmann & Singer, 1986; Giaschi, Regan, Kraft, & Hong, 1992; Hess & Holliday, 1992; Ho et al., 2005; Levi & Klein, 1983; Levi & Klein, 1985; Simmers, Ledgeway, Hess, & McGraw, 2003; Sireteanu, Lagreze, & Constantinescu, 1993). Treatment for amblyopia includes detection and correction of the underlying ocular disorder.
The visual evoked potential (VEP) generated by the amblyopic visual system demonstrates reduced amplitude, prolonged latency, and increased variation in response timing (phase-misalignment). This study examined VEPs before and after occlusion therapy (OT) and whether phase-misalignment can account for the amblyopic VEP deficits. VEPs were recorded to 0.5–4 cycles/degree gratings in 10 amblyopic children (2–6 years age) before and after OT. Phase-misalignment was measured by Fourier analysis across a limited bandwidth. Signal-to-noise ratios (SNRs) were estimated from amplitude and phase synchrony in the Fourier domain. Responses were compared to VEPs corrected for phase-misalignment (individual epochs shifted in time to correct for the misalignment). Before OT, amblyopic eyes (AE) had significantly more phase-misalignment, latency prolongation, and lower SNR relative to the fellow eye. Phase-misalignment contributed significantly to low SNR but less so to latency delay in the AE. After OT, phase-alignment improved, SNR improved and latency shortened in the AE. Raw averaged waveforms from the AE improved after OT, primarily at higher spatial frequencies. Correcting for phase-misalignment in the AE sharpened VEP peak responses primarily at low spatial frequencies, but could not account for VEP waveform improvements in the AE after OT at higher spatial frequencies. In summary, VEP abnormalities from the AE are associated with phase-misalignment and reduced SNR possibly related to desynchronization of neuronal activity. The effect of OT on VEP responses is greater than that accounted for by phase-misalignment and SNR alone.
Linking assumptions in amblyopia
2013, Visual Neuroscience
Low-level processing deficits underlying poor contrast sensitivity for moving plaids in anisometropic amblyopia
2012, Visual Neuroscience

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Distortions in two-dimensional visual space perception in strabismic observers

Abstract

Vision Research

Applications of information theory to psychology

Monocular spatial distortion in strabismic amblyopia

Investigative Ophthalmology and Visual Science

Normal and abnormal space perception

American Journal of Optometry and Physiological Optics

Human cortical magnification factor and its relation to visual acuity

Experimental Brain Research

Identifying amblyopia using associated functions, acuity and nonacuity features

American Journal of Optometry and Physiological Optics

Spatial mechanisms for visual acuity deficits in strabismic and anisometropic amblyopia—developmental failure or adaptation?

Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes

Investigative Ophthalmology and Visual Science