Monocular Deprivation Research Articles

Monocular deprivation during the critical period alters neuronal tuning and the composition of visual circuitry.

Abnormal visual experience during a developmental critical period degrades cortical responsiveness. Yet how experience-dependent plasticity alters the response properties of individual neurons and composition of visual circuitry is unclear. Here, we measured with calcium imaging in alert mice how monocular deprivation (MD) during the developmental critical period affects tuning for binocularity, orientation, and spatial frequency for neurons in primary visual cortex. MD of the contralateral eye did not uniformly shift ocular dominance (OD) of neurons towards the fellow ipsilateral eye but reduced the number of monocular contralateral neurons and increased the number of monocular ipsilateral neurons. MD also impaired matching of preferred orientation for binocular neurons and reduced the percentage of neurons responsive at most spatial frequencies for the deprived contralateral eye. Tracking the tuning properties for several hundred neurons before and after MD revealed that the shift in OD is complex and dynamic, with many previously monocular neurons becoming binocular and binocular neurons becoming monocular. Binocular neurons that became monocular were more likely to lose responsiveness to the deprived contralateral eye if they were better matched for orientation prior to deprivation. In addition, the composition of visual circuitry changed as population of neurons more responsive to the deprived eye were exchanged for neurons with tuning properties more similar to the network of responsive neurons altered by MD. Thus, plasticity during the critical period adapts to recent experience by both altering the tuning of responsive neurons and recruiting neurons with matching tuning properties.

Microglia enable cross-modal plasticity by removing inhibitory synapses

Cross-modal plasticity is the repurposing of brain regions associated with deprived sensory inputs to improve the capacity of other sensory modalities. The functional mechanisms of cross-modal plasticity can indicate how the brain recovers from various forms of injury and how different sensory modalities are integrated. Here, we demonstrate that rewiring of the microglia-mediated local circuit synapse is crucial for cross-modal plasticity induced by visual deprivation (monocular deprivation [MD]). MD relieves the usual inhibition of functional connectivity between the somatosensory cortex and secondary lateral visual cortex (V2L). This results in enhanced excitatory responses in V2L neurons during whisker stimulation and a greater capacity for vibrissae sensory discrimination. The enhanced cross-modal response is mediated by selective removal of inhibitory synapse terminals on pyramidal neurons by the microglia in the V2L via matrix metalloproteinase 9 signaling. Our results provide insights into how cortical circuits integrate different inputs to functionally compensate for neuronal damage.

The early stage of adult ocular dominance plasticity revealed by near-infrared optical imaging of intrinsic signals

Long term monocular deprivation is considered to be necessary for the induction of significant ocular dominance plasticity in the adult visual cortex. In this study, we subjected adult mice to monocular deprivation for various durations and screened for changes in ocular dominance using dual-wavelength intrinsic signal optical imaging. We found that short-term deprivation was sufficient to cause a shift in ocular dominance and that these early-stage changes were detected only by near-infrared illumination. In addition, single-unit recordings showed that these early-stage changes primarily occurred in deep cortical layers. This early-stage ocular dominance shift was abolished by the blockade of NMDA receptors. In summary, our findings reveal an early phase of adult ocular dominance plasticity and provide the dynamics of adult plasticity.

Enriched binocular experience followed by sleep optimally restores binocular visual cortical responses in a mouse model of amblyopia

Studies of primary visual cortex have furthered our understanding of amblyopia, long-lasting visual impairment caused by imbalanced input from the two eyes during childhood, which is commonly treated by patching the dominant eye. However, the relative impacts of monocular vs. binocular visual experiences on recovery from amblyopia are unclear. Moreover, while sleep promotes visual cortex plasticity following loss of input from one eye, its role in recovering binocular visual function is unknown. Using monocular deprivation in juvenile male mice to model amblyopia, we compared recovery of cortical neurons’ visual responses after identical-duration, identical-quality binocular or monocular visual experiences. We demonstrate that binocular experience is quantitatively superior in restoring binocular responses in visual cortex neurons. However, this recovery was seen only in freely-sleeping mice; post-experience sleep deprivation prevented functional recovery. Thus, both binocular visual experience and subsequent sleep help to optimally renormalize bV1 responses in a mouse model of amblyopia.

NNOS-induced tyrosine nitration of TRKB impairs BDNF signaling and restrains neuronal plasticity.

Nitric oxide (NO) has been long recognized as an important modulator of neural plasticity, but characterization of the molecular mechanisms involved - specially the guanylyl cyclase-independent ones - has been challenging. There is evidence that NO could modify BDNF-TRKB signaling, a key mediator of neuronal plasticity. However, the mechanism underlying the interplay of NO and TRKB remains unclear. Here we show that NO induces nitration of the tyrosine 816 in the TRKB receptor in vivo and in vitro, and that post-translational modification inhibits TRKB phosphorylation and binding of phospholipase Cγ1 (PLCγ1) to this same tyrosine residue. Additionally, nitration triggers clathrin-dependent endocytosis of TRKB through the adaptor protein AP-2 and ubiquitination, thereby increasing translocation of TRKB away from the neuronal surface and directing it towards lysosomal degradation. Accordingly, inhibition of nitric oxide increases TRKB phosphorylation and TRKB-dependent neurite branching in neuronal cultures. In vivo, chronic inhibition of neuronal nitric oxide synthase (nNOS) dramatically reduced TRKB nitration and facilitated TRKB signaling in the visual cortex, and promoted a shift in ocular dominance upon monocular deprivation - an indicator of increased plasticity. Altogether, our data describe and characterize a new molecular brake on plasticity, namely nitration of TRKB receptors.

Experience-dependent functional plasticity and visual response selectivity of surviving subplate neurons in the mouse visual cortex

Subplate neurons are early-born cortical neurons that transiently form neural circuits during perinatal development and guide cortical maturation. Thereafter, most subplate neurons undergo cell death, while some survive and renew their target areas for synaptic connections. However, the functional properties of the surviving subplate neurons remain largely unknown. This study aimed to characterize the visual responses and experience-dependent functional plasticity of layer 6b (L6b) neurons, the remnants of subplate neurons, in the primary visual cortex (V1). Two-photon Ca2+ imaging was performed in V1 of awake juvenile mice. L6b neurons showed broader tunings for orientation, direction, and spatial frequency than did layer 2/3 (L2/3) and L6a neurons. In addition, L6b neurons showed lower matching of preferred orientation between the left and right eyes compared with other layers. Post hoc 3D immunohistochemistry confirmed that the majority of recorded L6b neurons expressed connective tissue growth factor (CTGF), a subplate neuron marker. Moreover, chronic two-photon imaging showed that L6b neurons exhibited ocular dominance (OD) plasticity by monocular deprivation during critical periods. The OD shift to the open eye depended on the response strength to the stimulation of the eye to be deprived before starting monocular deprivation. There were no significant differences in visual response selectivity prior to monocular deprivation between the OD changed and unchanged neuron groups, suggesting that OD plasticity can occur in L6b neurons showing any response features. In conclusion, our results provide strong evidence that surviving subplate neurons exhibit sensory responses and experience-dependent plasticity at a relatively late stage of cortical development.

Ketamine and its metabolite 2R,6R-hydroxynorketamine promote ocular dominance plasticity and release tropomyosin-related kinase B from inhibitory control without reducing perineuronal nets enwrapping parvalbumin interneurons.

Ketamine has been described as a fast-acting antidepressant, exerting effects in depressed patients and in preclinical models with a rapid onset of action. The typical antidepressant fluoxetine is known to induce plasticity in the adult rodent visual cortex, as assessed by a shift in ocular dominance, a classical model of brain plasticity, and a similar effect has been described for ketamine and its metabolite 2R,6R-hydroxynorketamine (R,R-HNK). Here, we demonstrate that ketamine (at 3 or 20 mg/kg) and R,R-HNK facilitated the shift in ocular dominance in monocularly deprived mice, after three injections, throughout the 7-day monocular deprivation regimen. Notably, the comparison between the treatments indicates a higher effect size of R,R-HNK compared with ketamine. Treatment with ketamine or R,R-HNK failed to influence the levels of perineuronal nets (PNNs) surrounding parvalbumin-positive interneurons. However, we observed in vitro that both ketamine and R,R-HNK are able to disrupt the tropomyosin-related kinase B (TRKB) interaction with the protein tyrosine phosphatase sigma (PTPσ), which upon binding to PNNs dephosphorylates TRKB. These results support a model where diverse drugs promote the reinstatement of juvenile-like plasticity by directly binding TRKB and releasing it from PTPσ regulation, without necessarily reducing PNNs deposits.

Up-Regulation of NLRP3 in the Sclera Correlates with Myopia Progression in a Form-Deprivation Myopia Mouse Model.

NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) is a common inflammatory factor that induces inflammation by increasing the expression of related cytokines. Although the NLRP3 inflammasome has been implicated in many ophthalmic diseases, its role in myopia is largely unknown. The aim of this study was to explore the relationship between myopia progression and the NLRP3 pathway. A form-deprivation myopia (FDM) mouse model was used. Different degrees of myopic shift were achieved via monocular form deprivation with 0-, 2-, and 4-week covering, and by 4-week covering followed by 1-week uncovering (the blank, FDM2, FDM4, and FDM5 groups, respectively) in both wild-type and NLRP3 (-/-) C57BL/6J mice. Axial length and refractive power were measured to assess the specific degree of myopic shift. The protein levels of NLRP3 and of related cytokines in the sclera were evaluated by Western blotting and immunohistochemistry. Collagen I and matrix metalloproteinase-2 (MMP-2), which affect extracellular matrix (ECM) remodeling of the sclera, were also examined to clarify the possible underlying mechanism. In wild-type mice, the FDM4 group had the most significant myopic shift. Both the increase in refractive power and the elongation in axial length were significantly different between the experimental and control eyes in the FDM2 group. The protein levels of NLRP3, caspase-1, IL-1β, and IL-18 were significantly up-regulated in the FDM4 group compared to the other groups. The myopic shift was reversed and there was less up-regulation of cytokines in the FDM5 group compared to the FDM4 group. MMP-2 expression showed similar trends to NLRP3, while collagen I expression was inversely correlated. Similar results were found in NLRP3 -/- mice, although there was less myopic shift and less obvious changes in cytokine expression in the treatment groups as compared to the wild-type mice. In the blank group, no significant differences were found in refraction and axial length between wild-type mice and NLRP3 -/- mice of the same age. NLRP3 activation in the sclera could be involved in myopia progression in the FDM mouse model. Activation of the NLRP3 pathway up-regulated MMP-2 expression, which in turn affected collagen I and caused scleral ECM remodeling, eventually affecting myopic shift.

Internal neural states influence the short-term effect of monocular deprivation in human adults.

The adult human visual system maintains the ability to be altered by sensory deprivation. What has not been considered is whether the internal neural states modulate visual sensitivity to short-term monocular deprivation. In this study we manipulated the internal neural state and reported changes in intrinsic neural oscillations with a patched eye open or closed. We investigated the influence of eye open/eye closure on the unpatched eye's contrast sensitivity and ocular dominance (OD) shifts induced by short-term monocular deprivation. The results demonstrate that internal neural states influence not only baseline contrast sensitivity but also the extent to which the adult visual system can undergo changes in ocular dominance.

Rapid synaptic and gamma rhythm signature of mouse critical period plasticity

Early-life experience enduringly sculpts thalamocortical (TC) axons and sensory processing. Here, we identify the very first synaptic targets that initiate critical period plasticity, heralded by altered cortical oscillations. Monocular deprivation (MD) acutely induced a transient (<3 h) peak in EEG γ-power (~40 Hz) specifically within the visual cortex, but only when the critical period was open (juvenile mice or adults after dark-rearing, Lynx1-deletion, or diazepam-rescued GAD65-deficiency). Rapid TC input loss onto parvalbumin-expressing (PV) inhibitory interneurons (but not onto nearby pyramidal cells) was observed within hours of MD in a TC slice preserving the visual pathway - again once critical periods opened. Computational TC modeling of the emergent γ-rhythm in response to MD delineated a cortical interneuronal gamma (ING) rhythm in networks of PV-cells bearing gap junctions at the start of the critical period. The ING rhythm effectively dissociated thalamic input from cortical spiking, leading to rapid loss of previously strong TC-to-PV connections through standard spike-timing-dependent plasticity rules. As a consequence, previously silent TC-to-PV connections could strengthen on a slower timescale, capturing the gradually increasing γ-frequency and eventual fade-out over time. Thus, ING enables cortical dynamics to transition from being dominated by the strongest TC input to one that senses the statistics of population TC input after MD. Taken together, our findings reveal the initialsynaptic events underlying critical period plasticity and suggest that the fleeting ING accompanying a brief sensory perturbation may serve as a robust readout of TC network state with which to probe developmental trajectories.

ARC/Arg3.1 expression in the lateral geniculate body of monocular form deprivation amblyopic kittens

PurposeThe present study compared the expression of activity-regulated cytoskeleton-associated protein (ARC/Arg3.1) in the lateral geniculate body between form deprivation amblyopia kittens and normal kittens to examine the significance of ARC/Arg3.1 in the lateral geniculate body in the pathogenesis of amblyopia.MethodsTwenty kittens were randomly divided into an experimental group (n = 10) and a control group (n = 10). Black opaque covering cloth was used to cover the right eye of kittens in the experimental group. Pattern visual evoked potentials (PVEP) were detected weekly in all kittens. The expression of the ARC/Arg3.1 gene was detected by immunohistochemistry and in situ hybridization, and apoptosis of lateral geniculate body cells was detected by TUNEL.ResultsPVEP detection showed that at the age of 5 and 7 weeks, the latency of P100 in the right eye of the experimental group was higher than that of the other three groups (P < 0.05), and the amplitude of P100 was lower than that of the other three groups (P < 0.05). The expression of ARC/Arg3.1 protein (P < 0.05) and mRNA (P < 0.05) in the lateral geniculate body of the experimental group was significantly lower than that of the control group. The level of neuronal apoptosis in the experimental group was higher than that in the control group (P < 0.05). The expression of the ARC/Arg3.1 gene was negatively correlated with the apoptosis level of lateral geniculate body neurons.ConclusionsThe expression of ARC/Arg3.1 is associated with monocular form deprivation amblyopia and apoptosis of lateral geniculate body cells.

Effect of fasting on short-term visual plasticity in adult humans.

Brain plasticity and function is impaired in conditions of metabolic dysregulation, such as obesity. Less is known on whether brain function is also affected by transient and physiological metabolic changes, such as the alternation between fasting and fed state. Here we asked whether these changes affect the transient shift of ocular dominance that follows short-term monocular deprivation, a form of homeostatic plasticity. We further asked whether variations in three of the main metabolic and hormonal pathways affected in obesity (glucose metabolism, leptin signalling and fatty acid metabolism) correlate with plasticity changes. We measured the effects of 2 h monocular deprivation in three conditions: post-absorptive state (fasting), after ingestion of a standardised meal and during infusion of glucagon-like peptide-1 (GLP-1), an incretin physiologically released upon meal ingestion that plays a key role in glucose metabolism. We found that short-term plasticity was less manifest in fasting than in fed state, whereas GLP-1 infusion did not elicit reliable changes compared to fasting. Although we confirmed a positive association between plasticity and supraphysiological GLP-1 levels, achieved by GLP-1 infusion, we found that none of the parameters linked to glucose metabolism could predict the plasticity reduction in the fasting versus fed state. Instead, this was selectively associated with the increase in plasma beta-hydroxybutyrate (B-OH) levels during fasting, which suggests a link between neural function and energy substrates alternative to glucose. These results reveal a previously unexplored link between homeostatic brain plasticity and the physiological changes associated with the daily fast-fed cycle.

Primate monocular vision is intrinsically unstable: a side-effect of binocular homeostasis

Short-term deprivation of one eye of 1-2 hours in human adults results in reciprocal changes in the interocular balance that last 30-90 minutes, assumed to be the consequence of a change in the contrast gain within the binocular circuitry. What is not known is how these changes emerge and with what dynamic. One possibility is that they are initiated once the patch is removed. The alternative is that they result from a dynamic build-up from the moment the patch is applied. In this study, we measure the monocular dynamics of the non-deprived eye activation during the deprivation of the other eye in humans, using psychophysics, and in awake non-human primates, using functional ultrasound imaging (fUS) of the primary visual cortex (V1). In humans, we show that the contrast threshold increases overtime during the deprivation of the other eye. This observation indicates that the patching effect slowly builds up over the deprivation period at a binocular site. In the awake macaque, we show that during monocular deprivation the cerebral blood volume (CBV) increases in the non-deprived eye ocular-dominance bands, but not the deprived eye bands with similar dynamics as observed in human psychophysics. We show that human behavioral results can be predicted by a simple interocular normalization model that uses non-human primate CBV dynamics as a descriptor of the normalization pool activity. In conclusion, our results highlight a hitherto unknown feature of primate vision: monocular vision per se is intrinsically unstable.

Cofilin 1 Is Dynamically Modulated During Postnatal Development and by Visual Input in the Mouse Visual Cortex

Cofilin 1 is an actin depolymerizing protein playing a fundamental role in the turnover of actin filaments specifically in dendritic spines, where it has been associated with structural and functional plasticity processes. Using a differential proteomic approach, we recently identified cofilin 1 as a potential candidate for controlling plasticity levels in the mouse visual cortex. Here, we focus on analyzing the expression of cofilin 1 and of its serine-3 phosphorylated inactive form in the mouse visual cortex during postnatal development and its modulation by visual input. Western blot experiments showed that cofilin 1 decreases from the critical period to the adult stage, in correlation with the decreasing level of cortical plasticity, and that monocular deprivation increases its expression in the cortex contralateral to the deprived eye during the critical period but not in the adult stage. By immunohistochemistry, we identified that the phospho-cofilin 1 immunopositive signal is homogeneously expressed along the different layers of the mouse visual cortex and that it increases during postnatal development. Furthermore, monocular deprivation increases the phospho-cofilin 1 signal in the contralateral cortex to the deprived eye during the critical period but not in the adult stage. Altogether, these results suggest that cofilin 1 and its modification by phosphorylation are relevant players in the processes controlling experience-dependent plasticity in the mouse visual cortex.

Short-Term Monocular Deprivation in Adult Humans Alters Functional Brain Connectivity Measured With Ultra-High Field Magnetic Resonance Imaging

Short-Term Monocular Deprivation in Adult Humans Alters Functional Brain Connectivity Measured With Ultra-High Field Magnetic Resonance Imaging

Neuromodulation in the developing visual cortex after long-term monocular deprivation.

Neural dynamics are altered in the primary visual cortex (V1) during critical period monocular deprivation (MD). Synchronization of neural oscillations is pertinent to physiological functioning of the brain. Previous studies have reported chronic disruption of V1 functional properties such as ocular dominance, spatial acuity, and binocular matching after long-term monocular deprivation (LTMD). However, the possible neuromodulation and neural synchrony has been less explored. Here, we investigated the difference between juvenile and adult experience-dependent plasticity in mice from intracellular calcium signals with fluorescent indicators. We also studied alterations in local field potentials power bands and phase-amplitude coupling (PAC) of specific brain oscillations. Our results showed that LTMD in juveniles causes higher neuromodulatory changes as seen by high-intensity fluorescent signals from the non-deprived eye (NDE). Meanwhile, adult mice showed a greater response from the deprived eye (DE). LTMD in juvenile mice triggered alterations in the power of delta, theta, and gamma oscillations, followed by enhancement of delta-gamma PAC in the NDE. However, LTMD in adult mice caused alterations in the power of delta oscillations and enhancement of delta-gamma PAC in the DE. These markers are intrinsic to cortical neuronal processing during LTMD and apply to a wide range of nested oscillatory markers.

Fallopia Japonica and Prunella vulgaris inhibit myopia progression by suppressing AKT and NFκB mediated inflammatory reactions

BackgroundThe increased global incidence of myopia requires the establishment of therapeutic approaches. This study aimed to investigate the effect of Fallopia Japonica (FJ) and Prunella vulgaris (PV) extract on myopia caused by monocular form deprivation (MFD).MethodsWe used human retinal pigment epithelial cell to study the molecular mechanisms on how FJ extract (FJE) and PV extract (PVE) lowering the inflammation of the eye. The effect of FJE and PVE in MFD induced hamster model and explore the role of inflammation cytokines in myopia.ResultsFJE + PVE reduced IL-6, IL-8, and TNF-α expression in RPE cells. Furthermore, FJE and PVE inhibited inflammation by attenuating the phosphorylation of protein kinase B (AKT), and nuclear factor kappa-light-chain-enhancer of activated B (NF-κB) pathway. In addition, we report two resveratrol + ursolic acid compounds from FJ and PV and their inhibitory activities against IL-6, IL-8, and TNF-α expression levels in RPE cells treated with IL-6 and TNF-α. FJE, PVE, and FJE + PVE were applied to MFD hamsters and their axial length was measured after 21 days. The axial length showed statistically significant differences between phosphate-buffered saline- and FJE-, PVE-, and FJE + PVE-treated MFD eyes. FJE + PVE suppressed expressions of IL-6, IL-8, and TNF-α. They also inhibited myopia-related transforming growth factor-beta (TGF)-β1, matrix metalloproteinase (MMP)-2, and NF-κB expression while increasing type I collagen expression.ConclusionsOverall, these results suggest that FJE + PVE may have a therapeutic effect on myopia and be used as a potential treatment option.

Exercise does not enhance short-term deprivation-induced ocular dominance plasticity: evidence from dichoptic surround suppression

The input from the two eyes is combined in the brain. In this combination, the relative strength of the input from each eye is determined by the ocular dominance. Recent work has shown that this dominance can be temporarily shifted. Covering one eye with an eye patch for a few hours makes its contribution stronger. It has been proposed that this shift can be enhanced by exercise. Here, we test this hypothesis using a dichoptic surround suppression task, and with exercise performed according to American College of Sport Medicine guidelines. We measured detection thresholds for patches of sinusoidal grating shown to one eye. When an annular mask grating was shown simultaneously to the other eye, thresholds were elevated. The difference in the elevation found in each eye is our measure of relative eye dominance. We made these measurements before and after 120 min of monocular deprivation (with an eye patch). In the control condition, subjects rested during this time. For the exercise condition, 30 min of exercise were performed at the beginning of the patching period. This was followed by 90 min of rest. We find that patching results in a shift in ocular dominance that can be measured using dichoptic surround suppression. However, we find no effect of exercise on the magnitude of this shift. We further performed a meta-analysis on the four studies that have examined the effects of exercise on the dominance shift. Looking across these studies, we find no evidence for such an effect.

Transcranial random noise stimulation and exercise do not modulate ocular dominance plasticity in adults with normal vision.

Short-term deprivation of one eye by monocular patching causes a temporary increase in the contribution of that eye to binocular vision when the eye patch is removed. This effect, known as ocular dominance plasticity, provides a model of neuroplasticity within the human binocular visual system. We investigated whether physical exercise and the non-invasive brain stimulation technique transcranial random noise stimulation (tRNS), two interventions that may increase visual cortex neuroplasticity, enhance ocular dominance plasticity when delivered individually or in combination. Ocular dominance was measured using a grating rivalry test and a dichoptic letter contrast polarity judgment test. We observed robust ocular dominance changes for both outcome measures following 2-hour monocular deprivation; however, the magnitude of the effect was not influenced by exercise or tRNS. Ocular dominance plasticity may already be maximal after 2 hours of monocular deprivation in those with normal vision and therefore cannot be augmented by interventions designed to enhance neuroplasticity.

The shift in sensory eye dominance from short-term monocular deprivation exhibits no dependence on test spatial frequency

BackgroundStudies have shown that short-term monocular deprivation induces a shift in sensory eye dominance in favor of the deprived eye. Yet, how short-term monocular deprivation modulates sensory eye dominance across spatial frequency is not clear. To address this issue, we conducted a study to investigate the dependence of short-term monocular deprivation effect on test spatial frequency.MethodsTen healthy young adults (age: 24.7 ± 1.7 years, four males) with normal vision participated. We deprived their dominant eye with a translucent patch for 2.5 h. The interocular contrast ratio (dominant eye/non-dominant eye, i.e., the balance point [BP]), which indicates the contribution that the two eyes make to binocular combination, was measured using a binocular orientation combination task. We assessed if BPs at 0.5, 4 or 6 cycles/degree (c/d) change as a result of monocular deprivation. Different test spatial frequency conditions were conducted on three separate days in a random fashion.ResultsWe compared the BPs at 0.5, 4 and 6 c/d before and after monocular deprivation. The BPs were found to be significantly affected by deprivation, where sensory eye dominance shift to the deprived eye (F1.86, 16.76 = 33.09, P < 0.001). The changes of BP were consistent at 0.5, 4, and 6 c/d spatial frequencies (F2,18 = 0.15, P = 0.57).ConclusionThe sensory eye dominance plasticity induced by short-term deprivation is not dependent on test spatial frequency, suggesting it could provide a practical solution for amblyopic therapy that was concerned with the binocular outcome.