Stereo Sensitivity Research Articles

A Joint Lateral Motion-Stereo Constraint.

PurposeWe developed a stereo task that is based on a motion direction discrimination to examine the role that depth can play in disambiguating motion direction.MethodsIn this study, we quantified normal adults’ static and dynamic (i.e., laterally moving) stereoscopic performance using a psychophysical task, where we dichoptically presented randomly arranged, limited lifetime Gabor elements at two depth planes (one plane was at the fixation plane and the other at an uncrossed disparity relative to the fixation plane). Each plane contained half of the elements. For the dynamic condition, all elements were vertically oriented and moved to the left in one plane and to the right in another plane; for the static condition, the elements were horizontally oriented in one plane and vertically oriented in another plane.ResultsFor the range of motion speed that we measured (from 0.17°/s to 5.33°/s), we observed clear speed tuning of the stereo sensitivity (P = 3.0 × 10−5). The shape of this tuning did not significantly change with different spatial frequencies. We also found a significant difference in stereo sensitivity between stereopsis with static and laterally moving stimuli (speed = 0.67°/s; P = 0.004). Such difference was not evident when we matched the task between the static and moving stimuli.ConclusionsWe report that lateral motion modulates human global depth perception. This motion/stereo constraint is related to motion velocity not stimulus temporal frequency. We speculate that the processing of motion-based stereopsis of the kind reported here occurs in dorsal extrastriate cortex.

Binocular treatment in adult amblyopia is based on parvocellular or magnocellular pathway.

Amblyopia is speculated to be an untreatable disease in the patient, who is beyond the critical period of vision; however, currently, it is treatable in adults. This study aimed to elucidate whether the treatment is useful in both anisometropic amblyopia and strabismic amblyopia. In addition, the differences were detected between anisometropic amblyopia and strabismic amblyopia after the same perceptual treatment and whether the suppression in anisometropic amblyopia or strabismic amblyopia could be decreased before and after the treatment. A binocular perceptual learning was applied for the treatment, the suppression was measured, and the patients were followed up for 2 months after training. Anisometropic amblyopia and strabismic amblyopia groups were subjected to the assessment of stereo, visual acuity, contrast sensitivity, and suppression before and after the training. After 6 weeks of "Diploma Gabor Orientation Coherence" training, in the anisometropic amblyopia group, the outcomes of visual acuity (t = 3.114, p = 0.026) and contrast sensitivity (t = 7.786, p = 0.001) were increased significantly. While in the strabismic amblyopia group, the outcomes of stereo (t = 2.987, p = 0.040) and contrast sensitivity (t = 3.638, p = 0.022) were increased significantly. After Diploma Gabor Orientation Coherence training in the same frequency and in the same duration, the anisometropic amblyopia group got an improvement in visual acuity, but the strabismic amblyopia group got an improvement in stereo. As there are evidences to show that anisometropic amblyopia and strabismic amblyopia were injured in different pathways, we think the diverse results might come from the different pathway injury in anisometropic amblyopia and strabismic amblyopia.

Effects of Reduced Acuity and Stereo Acuity on Saccades and Reaching Movements in Adults With Amblyopia and Strabismus

Our previous work has shown that amblyopia disrupts the planning and execution of visually-guided saccadic and reaching movements. We investigated the association between the clinical features of amblyopia and aspects of visuomotor behavior that are disrupted by amblyopia. A total of 55 adults with amblyopia (22 anisometropic, 18 strabismic, 15 mixed mechanism), 14 adults with strabismus without amblyopia, and 22 visually-normal control participants completed a visuomotor task while their eye and hand movements were recorded. Univariate and multivariate analyses were performed to assess the association between three clinical predictors of amblyopia (amblyopic eye [AE] acuity, stereo sensitivity, and eye deviation) and seven kinematic outcomes, including saccadic and reach latency, interocular saccadic and reach latency difference, saccadic and reach precision, and PA/We ratio (an index of reach control strategy efficacy using online feedback correction). Amblyopic eye acuity explained 28% of the variance in saccadic latency, and 48% of the variance in mean saccadic latency difference between the amblyopic and fellow eyes (i.e., interocular latency difference). In contrast, for reach latency, AE acuity explained only 10% of the variance. Amblyopic eye acuity was associated with reduced endpoint saccadic (23% of variance) and reach (22% of variance) precision in the amblyopic group. In the strabismus without amblyopia group, stereo sensitivity and eye deviation did not explain any significant variance in saccadic and reach latency or precision. Stereo sensitivity was the best clinical predictor of deficits in reach control strategy, explaining 23% of total variance of PA/We ratio in the amblyopic group and 12% of variance in the strabismus without amblyopia group when viewing with the amblyopic/nondominant eye. Deficits in eye and limb movement initiation (latency) and target localization (precision) were associated with amblyopic acuity deficit, whereas changes in the sensorimotor reach strategy were associated with deficits in stereopsis. Importantly, more than 50% of variance was not explained by the measured clinical features. Our findings suggest that other factors, including higher order visual processing and attention, may have an important role in explaining the kinematic deficits observed in amblyopia.

Stereo sensitivity of exchange interactions in NiII and CuII heterospin complexes with 5-formylpyrrolyl-substituted nitroxides

5-Formylpyrrolyl-substituted nitronyl and imino nitroxide radicals HL1 and HL2 were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL1...HL1} pairs, the dominant interaction is the ferromagnetic exchange with J/kB = 8.8 K (Hamiltonian \(H = 2J\left( {\overrightarrow {{s_1}} \overrightarrow {{s_2}} } \right)\)). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L1)2], [Cu(L1)2], and [Ni(L2)2(MeOH)2]. In the complexes [Ni(L1)2] and [Cu(L1)2], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands.

Plasticity in adult amblyopia: a meta-review and analysis

Abstract Amblyopia is a neuro-developmental disorder involving a decrease in visual acuity that cannot be explained by ocular abnormalities. It affects 2-3% of the population and is the prevalent cause of monocular blindness. Patching of the amblyopic eye is a powerful treatment in early childhood but its effectiveness decreases with age, which has been attributed to decreased plasticity in the adult brain. In the last few decades new treatment methods including dichoptic training, perceptual learning and video games, were developed that improved visual acuity and/or stereoacuity in adult amblyopia. To understand the factors involved in adult plasticity in amblyopia, its clinical significance and to compare the treatments, we have used mean and individual participant data (IPD) meta-analyses on 19 studies with close to 200 individual scores. Our analysis showed that the average improvement in visual acuity (0.19 logMAR) was above mean test-retest reliability for acuity tests (0.14 logMAR) with 67% of subjects improving by more than this amount. Moreover, half of the subjects improved their stereo acuity by 2 octaves or more. The most important factor was the severity of amblyopia at the onset of treatment. Subjects with more severe amblyopia improved more on visual acuity and less on stereo sensitivity than those with the milder condition. Better binocularity was a predictor of improvements in stereo sensitivity. The different treatments, though employing very diverse strategies, yielded largely similar degrees of improvement on both measures. This suggests that any task involving sufficient engagement of the amblyopic eye could induce plasticity. We interpret this effect as the result of improvement in visual attention to the input from the amblyopic eye. Interocular suppression, which leads to amblyopia, could occur due to signal modulation by visual attention. Forcing visual attention to favor the amblyopic eye's input might release those suppressive influences, thus improving visual function. Meeting abstract presented at VSS 2015.

Behavioral Training as New Treatment for Adult Amblyopia: A Meta-Analysis and Systematic Review.

New behavioral treatment methods, including dichoptic training, perceptual learning, and video gaming, have been proposed to improve visual function in adult amblyopia. Here, we conducted a meta-analysis of these methods to investigate the factors involved in amblyopia recovery and their clinical significance. Mean and individual participant data meta-analyses were performed on 24 studies using the new behavioral methods in adults. Studies were identified using PubMed, Google Scholar, and published reviews. The new methods yielded a mean improvement in visual acuity of 0.17 logMAR with 32% participants achieving gains ≥ 0.2 logMAR, and a mean improvement in stereo sensitivity of 0.01 arcsec-1 with 42% of participants improving ≥2 octaves. The most significant predictor of treatment outcome was visual acuity at the onset of treatment. Participants with more severe amblyopia improved more on visual acuity and less on stereo sensitivity than those with milder amblyopia. Better initial stereo sensitivity was a predictor of greater gains in stereo sensitivity following treatment. Treatment type, amblyopia type, age, and training duration did not have any significant influence on visual and stereo acuity outcomes. Our analyses showed that some participants may benefit from the new treatments; however, clinical trials are required to confirm these findings. Despite the diverse nature of the new behavioral methods, the lack of significant differences in visual and stereo sensitivity outcomes among them suggests that visual attention-a common element among the varied treatment methods-may play an important role in amblyopia recovery.

Howard–Dolman stereovision test at different opponent colour stimuli

The purpose of this study was to investigate visual depth perception of real physical colour stimuli with red-green and blue-yellow opponency. We modified the Howard–Dolman stereotest where subjects should determine the closer of two bars emitting the light of definite colour placed in front of a CRT monitor served as colour background. Two-alternative forced-choice paradigms were used to determine depth perception threshold values. Thresholds close to 5–10 arcsec for luminance and colour contrast stimuli were revealed both for red-green and blue-yellow stimuli. A term, stereosensitivity – a reciprocal magnitude of the stereothreshold – was introduced to separately analyse luminance and colour contrast contributions in total depth perception. Comparing stereo sensitivity values for different colour stimuli, stereo sensitivity in case of red-green is still better than comparing to blue-yellow colour contrast. The colour and luminance contrast in CIE L*a*b* units (at least in the restricted dynamic range) could be applicable as a psychophysical metric to characterise stereo sensitivity. We suppose the colour and luminance contrast guided stereo mechanisms as two additive contributions in total stereo sense. Stereosense thresholds are more sensitive to luminance contrast changes as compared with colour contrast changes (in L*a*b* metric).

Stereo dynamics are not scale-dependent

The experiments reported here focus on the temporal dynamics of stereopsis in an effort to shed light on how low level mechanisms might contribute to the execution of coarse-to-fine processing in the human stereo system. Because previous studies have used a variety of stimuli and configurations, we assess the effect of exposure duration on stereo thresholds using band-limited Gabor patches for a range of stimulus configurations. In preliminary studies, we found that the best stereo sensitivity–spatial frequency relationship was obtained when using configurations in which the size and target–reference spacing were consistent with spatially scaled stimuli. Sub-optimal stereo sensitivity as a function of spatial frequency was observed when the size and separation were fixed. Further, we found that the temporal properties of stereopsis were consistently sustained in nature irrespective of the stimulus spatial frequency content. This latter finding suggests that if coarse-to-fine stereo processing does occur it does not follow as a consequence of the dynamics of low-level disparity transduction.

Spatial scale interactions in stereo sensitivity and the neural representation of binocular disparity.

How are binocular disparities encoded and represented in the human visual system? An 'encoding cube' diagram is introduced to visualise differences between competing models. To distinguish the models experimentally, the depth-increment-detection function (discriminating disparity d from d +/- delta d) was measured as a function of standing disparity (d) with spatially filtered random-dot stereograms of different centre spatial frequencies. Stereothresholds degraded more quickly as standing disparity was increased with stimuli defined by high rather than low centre spatial frequency. This is consistent with a close correlation between the spatial scale of detection mechanisms and the disparities they process. It is shown that a simple model, where discrimination is limited by the noisy ratio of outputs of three disparity-selective mechanisms at each spatial scale, can account for the data. It is not necessary to invoke a population code for disparity to model the depth-increment-detection function. This type of encoding scheme implies insensitivity to large interocular phase differences. Might the system have developed a strategy to disambiguate or shift the matches made at fine scales with those made at the coarse scales at large standing disparities? In agreement with Rohaly and Wilson, no evidence was found that this is so. Such a scheme would predict that stereothresholds determined with targets composed of compounds of high and low frequency should be superior to those of either component alone. Although a small stereoacuity benefit was found at small disparities, the more striking result was that stereothresholds for compound-frequency targets were actually degraded at large standing disparities. The results argue against neural shifting of the matching range of fine scales by coarse-scale matches posited by certain stereo models.

The suppression effect of simulated anisometropia

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs. As there is evidence that suppression scotomas are induced in the more defocused eye, the presence and approximate size of suppression scotomas induced with uni-ocular defocus was investigated in five binocularly normal subjects. The targets comprised a fusional lock and a suppression check for each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately +/- 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisometropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisometropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.

The suppression effect of simulated anisometropia

Although there is evidence that differential interocular image clarity degrades binocular performance (for example, reducing stereo sensitivity) little is known about how this sensitivity reduction occurs, As there is evidence that suppression scotomas are induced in the more defocused eye. the presence and approximate size of suppression scotomas induced with uni-ocular defocus was investigated in live binocularly normal subjects. The targets comprised a fusional lock and a suppression check For each eye and the task of each subject was to report the presence of the suppression check with varying amount of defocus. There was a range of simulated anisometropia over which suppression did not occur (approximately ± 0.50 DS). Thereafter the probability of suppressing a small foveal target increased approximately linearly until (the target was always suppressed. Greater amounts of simulated anisometropia produced larger suppression scotomas. However, less anisomeiropia was required to produce an equivalent sized suppression scotoma if greater amounts of fusional detail were provided. These results suggest that the decrement in binocular performance which accompanies simulated anisomeiropia may occur because of localized inhibition in the more defocused eye and is not solely due to loss of resolution in that eye.

Depth-increment detection function for individual spatial channels.

We have used stimuli with difference-of-Gaussian (DOG) luminance profiles to measure depth-increment thresholds within postulated spatial channels as functions of depth from the fixation plane. Stereoacuity was best with high-frequency DOG's presented at the fixation plane. Performance was relatively constant for spatial frequency above 2.4 cycles/deg, but it deteriorated as spatial frequency was decreased. Regardless of spatial frequency, stereo sensitivity declined rapidly as stimuli were presented away from the horopter. The falloff occurred more rapidly over the 0-20-arc-min range than over the 20-80-arc-min range. Depth was perceived over a broader range of disparity pedestals with low-spatial-frequency stimuli; however, the lowest thresholds were always obtained with the highest-frequency stimuli. Both the falloff of sensitivity with disparity pedestal and the disparity range of quantitative stereo depth lead to the conclusion that different size-tuned channels process disparity differently.

Disparity range for local stereopsis as a function of luminance spatial frequency

The disparity range for stereo sensitivity was investigated with spatially filtered bars, tuned narrowly over a broad range of spatial frequencies. When measured with narrow (high spatial frequency) bars the disparity range for stereopsis exceeded two orders of magnitude. The range was reduced with broad (low spatial frequency) bars by an elevation of stereothreshold that increased according to a constant 6deg phase disparity. The upper disparity limit also increased at broad spatial periods but at a lower rate. These size disparity correlations illustrate quantitative stereopsis along a continuum from fine to coarse disparities ( ± 2deg). A disparity matching task revealed that greater amounts of uncrossed than crossed disparity were required to match suprathreshold disparities. The ratio of standard/matched disparity was lower in both directions for small suprathreshold disparities subtended by broad than by narrow spatial periods. This selective reduction of stereo-efficiency ratio illustrates tuning to coarse disparities subtended by broad (low spatial frequency) stimuli and accounts for the marked reduction of stereoacuity caused by spectacle blur.

Lifting forces associated with contact lenses.

Measurements of the threshold of stereopsis under conditions in which a difference in monocular retinal illuminance exists indicate a decrease in sensitivity. Delaying one of the two binocular images was used as a means of investigating whether or not the decrease in stereo sensitivity due to differences in monocular retinal illuminances could be equated to changes in latency. The study indicates that a pure latency hypothesis is too simple a concept to account for the results.