Early cross-modal interactions and adult human visual cortical plasticity revealed by binocular rivalry

In this research binocular rivalry is used as a tool to investigate different aspects of visual and multisensory perception. Several experiments presented here demonstrated that touch specifically interacts with vision during binocular rivalry and that the interaction likely occurs at early stages of visual processing, probably V1 or V2. Another line of research also presented here demonstrated that human adult visual cortex retains an unexpected high degree of experience-dependent plasticity by showing that a brief period of monocular deprivation produced important perceptual consequences on the dynamics of binocular rivalry, reflecting a homeostatic plasticity. In summary, this work shows that binocular rivalry is a powerful tool to investigate different aspects of visual perception and can be used to reveal unexpected properties of early visual cortex

Learning to discriminate the eye‐of‐origin during continuous flash suppression

Helmholtz asked whether one could discriminate which eye is the origin of one's perception merely based on the retinal signals. Studies to date showed that participants' ability to tell the eye‐of‐origin most likely depends on contextual cues. Nevertheless, it has been shown that exogenous attention can enhance performance for monocularly presented stimuli. We questioned whether adults can be trained to discriminate the eye‐of‐origin of their perceptions and if this ability depends on the strength of the monocular channels. We used attentional feed‐forward training to improve the subject's eye‐of‐origin discrimination performance with voluntary attention. During training, participants received a binocular cue to inform them of the eye‐of‐origin of an upcoming target. Using continuous flash suppression, we also measured the signal strength of the monocular targets to see any possible modulations related to the cues. We collected confidence ratings from the participants about their eye‐of‐origin judgements to study in further detail whether metacognition has access to this information. Our results show that, even though voluntary attention did not alter the strength of the monocular channels, eye‐of‐origin discrimination performance improved following the training. A similar pattern was observed for confidence. The results from the feedforward attentional training and the increase in subjective confidence point towards a high‐level decisional mechanism being responsible for the eye‐of‐origin judgements. We propose that this high‐level process is informed by subtle sensory cues such as the differences in luminance or contrast in the two monocular channels

Binocular Rivalry Measured 2 Hours After Occlusion Therapy Predicts the Recovery Rate of the Amblyopic Eye in Anisometropic Children

Recent studies on adults have shown that short-term monocular deprivation boosts the deprived eye signal in binocular rivalry, reflecting homeostatic plasticity. Here we investigate whether homeostatic plasticity is present also during occlusion therapy for moderate amblyopia.PURPOSE. Recent studies on adults have shown that short-term monocular deprivation boosts the deprived eye signal in binocular rivalry, reflecting homeostatic plasticity. Here we investigate whether homeostatic plasticity is present also during occlusion therapy for moderate amblyopia. METHODS. Binocular rivalry and visual acuity (using Snellen charts for children) were measured in 10 children (mean age 6.2±6 1 years) with moderate anisometropic amblyopia before the beginning of treatment and at four intervals during occlusion therapy (2 hours, 1, 2, and 5 months). Visual stimuli were orthogonal gratings presented dichoptically through ferromagnetic goggles and children reported verbally visual rivalrous perception. Bangerter filters were applied on the spectacle lens over the best eye for occlusion therapy. RESULTS. Two hours of occlusion therapy increased the nonamblyopic eye predominance over the amblyopic eye compared with pretreatment measurements, consistent with the results in adults. The boost of the nonamblyopic eye was still present after 1 month of treatment, steadily decreasing afterward to reach pretreatment levels after 2 months of continuous occlusion. Across subjects, the increase in nonamblyopic eye predominance observed after 2 hours of occlusion correlated (rho =-0.65, P =0.04) with the visual acuity improvement of the amblyopic eye measured after 2 months of treatment. CONCLUSIONS. Homeostatic plasticity operates during occlusion therapy for moderate amblyopia and the increase in nonamblyopic eye dominance observed at the beginning of treatment correlates with the amblyopic eye recovery rate. These results suggest that binocular rivalry might be used to monitor visual cortical plasticity during occlusion therapy, although further investigations on larger clinical populations are needed to validate the predictive power of the technique

The duration effect of short-term monocular deprivation measured by binocular rivalry and binocular combination

: The ocular dominance shift observed after short-term monocular deprivation is a widely used measure of visual homeostatic plasticity in adult humans. Binocular rivalry and binocular combination techniques are used interchangeably to characterize homeostatic plasticity, sometimes leading to contradictory results. Here we directly compare the effect of short-term monocular deprivation on ocular dominance measured by either binocular rivalry or binocular combination and its dependence on the duration of deprivation (15 or 120 min) in the same group of participants. Our results show that both binocular rivalry and binocular combination provide reliable estimates of ocular dominance, which are strongly correlated across techniques both before and after deprivation. Moreover, while 15 min of monocular deprivation induce a larger shift of ocular dominance when measured using binocular combination compared to binocular rivalry, for both techniques, the shift in ocular dominance exhibits a strong dependence on the duration of monocular deprivation, with longer deprivation inducing a larger and longer-lasting shift in ocular dominance. Taken together, our results indicate that both binocular rivalry and binocular combination offer very consistent and reliable measurements of both ocular dominance and the effect short-term monocular deprivation

Response to short-term deprivation of the human adult visual cortex measured with 7T BOLD

Sensory deprivation during the post-natal 'critical period' leads to structural reorganization of the developing visual cortex. In adulthood, the visual cortex retains some flexibility and adapts to sensory deprivation. Here we show that short-term (2 hr) monocular deprivation in adult humans boosts the BOLD response to the deprived eye, changing ocular dominance of V1 vertices, consistent with homeostatic plasticity. The boost is strongest in V1, present in V2, V3 and V4 but absent in V3a and hMT+. Assessment of spatial frequency tuning in V1 by a population Receptive-Field technique shows that deprivation primarily boosts high spatial frequencies, consistent with a primary involvement of the parvocellular pathway. Crucially, the V1 deprivation effect correlates across participants with the perceptual increase of the deprived eye dominance assessed with binocular rivalry, suggesting a common origin. Our results demonstrate that visual cortex, particularly the ventral pathway, retains a high potential for homeostatic plasticity in the human adult

Response to short-term deprivation of the human adult visual cortex measured with 7T BOLD

International audienceSensory deprivation during the post-natal 'critical period' leads to structural reorganization of the developing visual cortex. In adulthood, the visual cortex retains some flexibility and adapts to sensory deprivation. Here we show that short-term (2 hr) monocular deprivation in adult humans boosts the BOLD response to the deprived eye, changing ocular dominance of V1 vertices, consistent with homeostatic plasticity. The boost is strongest in V1, present in V2, V3 and V4 but absent in V3a and hMT+. Assessment of spatial frequency tuning in V1 by a population Receptive-Field technique shows that deprivation primarily boosts high spatial frequencies, consistent with a primary involvement of the parvocellular pathway. Crucially, the V1 deprivation effect correlates across participants with the perceptual increase of the deprived eye dominance assessed with binocular rivalry, suggesting a common origin. Our results demonstrate that visual cortex, particularly the ventral pathway, retains a high potential for homeostatic plasticity in the human adult

A new counterintuitive training for adult amblyopia

International audienceObjectives: The aim of this study was to investigate whether short-term inverse occlusion, combined with moderate physical exercise, could promote the recovery of visual acuity and stereopsis in a group of adult anisometropic amblyopes. Methods: Ten adult anisometropic patients underwent six brief (2 h) training sessions over a period of 4 weeks. Each training session consisted in the occlu-sion of the amblyopic eye combined with physical exercise (intermittent cycling on a stationary bike). Visual acuity (measured with ETDRS charts), stereoacuity (measured with the TNO test), and sensory eye dominance (measured with binocular rivalry) were tested before and after each training session, as well as in follow-up visits performed 1 month, 3 months, and 1 year after the end of the training. Results: After six brief (2 h) training sessions, visual acuity improved in all 10 patients (0.15 AE 0.02 LogMar), and six of them also recovered stereopsis. The improvement was preserved for up to 1 year after training. A pilot experiment suggested that physical activity might play an important role for the recovery of visual acuity and stereopsis. Conclusions: Our results suggest a noninvasive training strategy for adult human amblyopia based on an inverse-occlusion procedure combined with physical exercise