Andrea Pavan

Improvement of uncorrected visual acuity and contrast sensitivity with perceptual learning and transcranial random noise stimulation in individuals with mild myopia

Perceptual learning has been shown to produce an improvement of visual acuity (VA) and contrast sensitivity (CS) both in subjects with amblyopia and refractive defects such as myopia or presbyopia. Transcranial random noise stimulation (tRNS) has proven to be efficacious in accelerating neural plasticity and boosting perceptual learning in healthy participants. In this study, we investigated whether a short behavioral training regime using a contrast detection task combined with online tRNS was as effective in improving visual functions in participants with mild myopia compared to a 2-month behavioral training regime without tRNS (Camilleri et al., 2014). After 2 weeks of perceptual training in combination with tRNS, participants showed an improvement of 0.15 LogMAR in uncorrected VA (UCVA) that was comparable with that obtained after 8 weeks of training with no tRNS, and an improvement in uncorrected CS (UCCS) at various spatial frequencies (whereas no UCCS improvement was seen after 8 weeks of training with no tRNS). On the other hand, a control group that trained for 2 weeks without stimulation did not show any significant UCVA or UCCS improvement. These results suggest that the combination of behavioral and neuromodulatory techniques can be fast and efficacious in improving sight in individuals with mild myopia.

The application of online transcranial random noise stimulation and perceptual learning in the improvement of visual functions in mild myopia

It has recently been demonstrated how perceptual learning, that is an improvement in a sensory/perceptual task upon practice, can be boosted by concurrent high-frequency transcranial random noise stimulation (tRNS). It has also been shown that perceptual learning can generalize and produce an improvement of visual functions in participants with mild refractive defects. By using three different groups of participants (single-blind study), we tested the efficacy of a short training (8 sessions) using a single Gabor contrast-detection task with concurrent hf-tRNS in comparison with the same training with sham stimulation or hf-tRNS with no concurrent training, in improving visual acuity (VA) and contrast sensitivity (CS) of individuals with uncorrected mild myopia. A short training with a contrast detection task is able to improve VA and CS only if coupled with hf-tRNS, whereas no effect on VA and marginal effects on CS are seen with the sole administration of hf-tRNS. Our results support the idea that, by boosting the rate of perceptual learning via the modulation of neuronal plasticity, hf-tRNS can be successfully used to reduce the duration of the perceptual training and/or to increase its efficacy in producing perceptual learning and generalization to improved VA and CS in individuals with uncorrected mild myopia.

The effect of spatial frequency on peripheral collinear facilitation.

The detection of a Gabor patch (target) can be decreased or improved by the presence of co-oriented Gabor patches (flankers) having the same spatial frequency as the target. These phenomena are thought to be mediated by lateral interactions. Depending on the distance between target and flankers, commonly defined as a multiple of the wavelength (λ) of the carrier, flankers can increase or decrease a targets detectability. Studies with foveal presentation showed that for target-to-flankers distances<2λ contrast thresholds for the central target increase, while for target-to-flankers distances>3λ contrast thresholds decrease. Earlier studies on collinear facilitation at the near-periphery of the visual field (4° of eccentricity) showed inconsistent facilitation (Shani & Sagi, 2005, Vision Research, 45, 2009-2024) whereas more recent studies showed consistent facilitation for larger separations (7-8λ) (Maniglia et al., 2011, PLoS ONE, 6, e25568; Lev & Polat, 2011, Vision Research, 51, 2488-2498). However, all of these studies used medium-to-high spatial frequencies (3-8 cpd). In this study we tested lower spatial frequencies (1, 2, and 3 cpd) with different target-to-flankers distances. The rationale was that near-peripheral vision is tuned for lower spatial frequencies and this could be reflected in collinear facilitation. Results show consistent collinear facilitation at 8λ for all the spatial frequencies tested, but also show collinear facilitation at shorter target-to-flanker distance (6λ) for the lowest spatial frequencies tested (1 cpd). Additionally, collinear facilitation decreases as spatial frequency increases; opposite to the findings of Polat (2009, Spatial Vision, 22, 179-193) in the fovea, indicating a different spatial frequency tuning between foveal and peripheral lateral interactions.

Action Video Games Improve Direction Discrimination of Parafoveal Translational Global Motion but Not Reaction Times

Playing action video games enhances visual motion perception. However, there is psychophysical evidence that action video games do not improve motion sensitivity for translational global moving patterns presented in fovea. This study investigates global motion perception in action video game players and compares their performance to that of non-action video game players and non-video game players. Stimuli were random dot kinematograms presented in the parafovea. Observers discriminated the motion direction of a target random dot kinematogram presented in one of the four visual quadrants. Action video game players showed lower motion coherence thresholds than the other groups. However, when the task was performed at threshold, we did not find differences between groups in terms of distributions of reaction times. These results suggest that action video games improve visual motion sensitivity in the near periphery of the visual field, rather than speed response.

Suppressive effects on motion discrimination induced by transient flankers are reduced by perceptual learning.

We investigated spatial suppression of a drifting Gabor target of 0.5 c/° induced by adjacent and iso-oriented stationary Gabors (flankers) whose spatial frequency differed by ±1 and ±2 octaves to that of the drifting target. Stimuli (target and flankers) were presented for 33 ms. Results showed greater spatial suppression when the spatial frequency of the stationary but transient flanking Gabors was either equal or 1-2 octaves lower than when it was 1-2 octaves higher than the targets spatial frequency. This asymmetry was evident only for the drifting target, but not for the stationary target. In addition, we investigated whether perceptual learning (PL) reduced the spatial suppression induced by the flankers. We found that PL increased contrast sensitivity for the target, but only when it was reduced by the lateral masking flankers, and its effect did not transfer to an isolated drifting target of equal or higher spatial frequency. These results suggest that PL selectively affects suppressive interactions rather than contrast gain. We suggest that the suppressive effect of low spatial frequency flankers and the lack of suppression with high spatial frequency flankers may reflect two complementary phenomena: camouflage by the transient flankers (i.e., context) and breaking of camouflage by form-motion segmentation. Camouflage may result because both target and flankers activate the motion (magnocellular) system. Breaking of camouflage instead may occur when target and flankers spatial frequency are more suitable for quasi-independent activation of the form system (by the flankers) and the motion system (by the target).

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

ABSTRACT 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. HIGHLIGHTSPerceptual training improves visual functions in adults with amblyopia.With a short training we improved contrast sensitivity in adults with amblyopia.When the training was coupled with hf‐tRNS improvement transferred to visual acuity.No transfer to visual acuity was observed with Sham stimulation.hf‐tRNS might boost transfer of perceptual learning to untrained visual functions.

The neural basis of form and form-motion integration from static and dynamic translational Glass patterns: A rTMS investigation

&NA; A long‐held view of the visual system is that form and motion are independently analysed. However, there is physiological and psychophysical evidence of early interaction in the processing of form and motion. In this study, we used a combination of Glass patterns (GPs) and repetitive Transcranial Magnetic Stimulation (rTMS) to investigate in human observers the neural mechanisms underlying form‐motion integration. GPs consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented stimulus. GPs can be either static or dynamic. Dynamic GPs have both a form component (i.e., orientation) and a non‐directional motion component along the orientation axis. GPs were presented in two temporal intervals and observers were asked to discriminate the temporal interval containing the most coherent GP. rTMS was delivered over early visual area (V1/V2) and over area V5/MT shortly after the presentation of the GP in each interval. The results showed that rTMS applied over early visual areas affected the perception of static GPs, but the stimulation of area V5/MT did not affect observers performance. On the other hand, rTMS was delivered over either V1/V2 or V5/MT strongly impaired the perception of dynamic GPs. These results suggest that early visual areas seem to be involved in the processing of the spatial structure of GPs, and interfering with the extraction of the global spatial structure also affects the extraction of the motion component, possibly interfering with early form‐motion integration. However, visual area V5/MT is likely to be involved only in the processing of the motion component of dynamic GPs. These results suggest that motion and form cues may interact as early as V1/V2. Graphical abstract Figure. No caption available. HighlightsAssessed impact of rTMS over V1/V2 and V5/MT on perception of Glass patterns (GPs).rTMS over V1/V2 interfered with perception of both static and dynamic GPs.rTMS over V5/MT interfered only with perception of dynamic GPs.Early visual areas encode the global spatial structure of all GPs.Area V5/MT is important for signalling the dynamic properties of GPs.

No priming for global motion in crowding

There is psychophysical evidence that low-level priming, e.g., from oriented gratings, as well as high-level semantic priming, survives crowding. We investigated priming for global translational motion in crowded and noncrowded conditions. The results indicated that reliable motion priming occurs in the noncrowded condition, but motion priming does not survive crowding. Crowding persisted despite variations in the direction of the flankers with respect to the primes direction. Motion priming was still absent under crowding when 85% of the flankers moved in the same direction as the prime. Crowding also persisted despite variations in the speed of the flankers relative to the prime even when the flankers speed was four times slower than the speed of the prime. However, a priming effect was evident when the primes spatial location was precued and its distance to the flankers increased, suggesting a release from crowding. These results suggest that transient attention induced by precueing the spatial location of the prime may improve subjects ability to discriminate its direction. Spatial cueing could act to decrease the integration field, thereby diminishing the influence of nearby distracters. In an additional experiment in which we used fewer flankers, we found a priming effect under conditions in which the interelement distance varied between flankers and prime. Overall, the results suggest that motion priming is strongly affected by crowding, but transient attention can partially retrieve such facilitation.

The effects of high-frequency transcranial random noise stimulation (hf-tRNS) on global motion processing: An equivalent noise approach

BACKGROUNDnHigh frequency transcranial random noise stimulation (hf-tRNS) facilitates performance in several perceptual and cognitive tasks, however, little is known about the underlying modulatory mechanisms.nnnOBJECTIVEnIn this study we compared the effects of hf-tRNS to those of anodal and cathodal tDCS in a global motion direction discrimination task. An equivalent noise (EN) paradigm was used to assess how hf-tRNS modulates the mechanisms underlying local and global motion processing.nnnMETHODnMotion coherence threshold and slope of the psychometric function were estimated using an 8AFC task in which observers had to discriminate the motion direction of a random dot kinematogram presented either in the left or right visual hemi-field. During the task hf-tRNS, anodal and cathodal tDCS were delivered over the left hMT+. In a subsequent experiment we implemented an EN paradigm in order to investigate the effects of hf-tRNS on the mechanisms involved in visual motion integration (i.e., internal noise and sampling).nnnRESULTSnhf-tRNS reduced the motion coherence threshold but did not affect the slope of the psychometric function, suggesting no modulation of stimulus discriminability. Anodal and cathodal tDCS did not produce any modulatory effects. EN analysis in the last experiment found that hf-tRNS modulates sampling but not internal noise, suggesting that hf-tRNS modulates the integration of local motion cues.nnnCONCLUSIONnhf-tRNS interacts with the output neurons tuned to directions near to the directional signal, incrementing the signal-to-noise ratio and the pooling of local motion cues and thus increasing the sensitivity for global moving stimuli.

The spatial range of peripheral collinear facilitation

In visual perception contextual influences on the detection of a target stimulus have been widely investigated. A striking number of studies have shown that detection thresholds for a central Gabor patch (target) can be modulated by the presence of co-oriented and collinear high contrast Gabor stimuli (flankers) with the same phase and spatial frequency. This phenomenon is thought to be mediated by lateral interactions between neurons receptive fields, and depending on the distance between the central target and flankers modulation can be facilitatory or suppressive. More specifically, collinear facilitation can be observed for target-to-flankers distances beyond two times the wavelength (λ) of the Gabors carrier, while for shorter distances (< 2λ) there is a suppressive effect. Collinear facilitation vanishes for target-to-flankers distances larger than 12λ. Recently, a series of studies showed the existence of such effects with stimuli presented at 4° of eccentricity, but only for larger target-to-flankers distances than in the fovea (>7λ). The aim of this study is to assess whether peripheral collinear facilitation extends beyond the limits of foveal presentation, shifting the peak of collinear facilitation towards higher target-to-flankers distances. We measured contrast detection thresholds for different spatial frequencies (1-6 cpd) and target-to-flankers distances (6-16λ), with configuration presented at 4° of eccentricity. Results showed that the range of collinear facilitation extends beyond 14λ for the higher spatial frequencies tested (4 and 6 cpd), while for the lowest spatial frequency (1cpd) it returns to baseline already at 10λ. One of the reasons for this reduced range of facilitation might be that for low spatial frequencies time integration window is a constrain for facilitation when flankers are too far away. Moreover, we found that the peak of collinear facilitation shifts towards larger target-to-flankers distances as the spatial frequency increases, a phenomenon never reported for peripheral or for foveal presentation. Meeting abstract presented at VSS 2015.