tRNS boosts visual perceptual learning in participants with bilateral macular degeneration.

Perceptual learning (PL) has shown promise in enhancing residual visual functions in patients with age-related macular degeneration (MD), however it requires prolonged training and evidence of generalization to untrained visual functions is limited. Recent studies suggest that combining transcranial random noise stimulation (tRNS) with perceptual learning produces faster and larger visual improvements in participants with normal vision. Thus, this approach might hold the key to improve PL effects in MD.

Processing of translational, radial and rotational optic flow in older adults.

Aging impacts human observer's performance in a wide range of visual tasks and notably in motion discrimination. Despite numerous studies, we still poorly understand how optic flow processing is impacted in healthy older adults. Here, we estimated motion coherence thresholds in two groups of younger (age: 18-30, n = 42) and older (70-90, n = 42) adult participants for the three components of optic flow (translational, radial and rotational patterns).

Optic Flow Processing in Patients With Macular Degeneration.

Purpose: Optic flow processing was characterized in patients with macular degeneration (MD).

Methods: Twelve patients with dense bilateral scotomas and 12 age- and gender-matched control participants performed psychophysical experiments. Stimuli were dynamic random-dot kinematograms projected on a large screen.

An egocentric straight-ahead bias in primate's vision.

As we plan to reach or manipulate objects, we generally orient our body so as to face them. Other objects occupying the same portion of space will likely represent potential obstacles for the intended action. Thus, either as targets or as obstacles, the objects located straight in front of us are often endowed with a special behavioral status.

Combining fixation and lateral masking training enhances perceptual learning effects in patients with macular degeneration.

Macular degeneration (MD), a retinal disease affecting central vision, represents the leading cause of visual impairment in the Western world, and MD patients face severe limitations in daily activities like reading and face recognition. A common compensation strategy adopted by these patients involves the use of a region in the spared peripheral retina as a new fixation spot and oculomotor reference (preferred retinal locus, or PRL). Still, peripheral vision is characterized by poorer visual acuity, fixation stability, and larger crowding zones that further hinder processes like object recognition, visual search, and reading.

Wide-field retinotopy reveals a new visuotopic cluster in macaque posterior parietal cortex.

We investigated the visuotopic organization of macaque posterior parietal cortex (PPC) by combining functional imaging (fMRI) and wide-field retinotopic mapping in two macaque monkeys. Whole brain blood-oxygen-level-dependent (BOLD) signal was recorded while monkeys maintained central fixation during the presentation of large rotating wedges and expending/contracting annulus of a "shaking" fruit basket, designed to maximize the recruitment of PPC neurons. Results of the surface-based population receptive field (pRF) analysis reveal a new cluster of four visuotopic areas at the confluence of the parieto-occipital and intra-parietal sulci, in a location previously defined histologically and anatomically as the posterior intra-parietal (PIP) region.

Dynamics of the straight-ahead preference in human visual cortex.

The objects located straight-ahead of the body are preferentially processed by the visual system. They are more rapidly detected and evoke stronger BOLD responses in early visual areas than elements that are retinotopically identical but located at eccentric spatial positions. To characterize the dynamics of the underlying neural mechanisms, we recorded in 29 subjects the EEG responses to peripheral targets differing solely by their locations with respect to the body.

TMS reveals inhibitory extrastriate cortico-cortical feedback modulation of V1 activity in humans.

The interaction between the primary visual cortex (V1) and extrastriate visual areas provides the first building blocks in our perception of the world. V2, in particular, seems to play a crucial role in shaping contextual modulation information through feedback projections to V1. However, whether this feedback is inhibitory or excitatory is still unclear.

Asymmetry of pictorial space: A cultural phenomenon.

Art experts have argued that the mirror reversal of pictorial artworks produces an alteration of their spatial content. However, this putative asymmetry of the pictorial space remains to be empirically proved and causally explained. Here, we address these issues with the "corridor illusion," a size illusion triggered by the pictorial space of a receding corridor.

tRNS boosts perceptual learning in peripheral vision.

Visual crowding, the difficulty of recognizing elements when surrounded by similar items, is a widely studied perceptual phenomenon and a trademark characteristic of peripheral vision. Perceptual Learning (PL) has been shown to reduce crowding, although a large number of sessions is required to observe significant improvements. Recently, transcranial random noise stimulation (tRNS) has been successfully used to boost PL in low-level foveal tasks (e.

Spontaneous and training-induced cortical plasticity in MD patients: Hints from lateral masking.

Macular degeneration (MD) affects central vision and represents the leading cause of visual diseases in elderly population worldwide. As a consequence of central vision loss, MD patients develop a preferred retinal locus (PRL), an eccentric fixation point that replaces the fovea. Here, our aim was to determine whether and to what extent spontaneous plasticity takes place in the cortical regions formerly responding to central vision and whether a visual training based on perceptual learning (PL) can boost this plasticity within the PRL area.

Processing of Egomotion-Consistent Optic Flow in the Rhesus Macaque Cortex.

The cortical network that processes visual cues to self-motion was characterized with functional magnetic resonance imaging in 3 awake behaving macaques. The experimental protocol was similar to previous human studies in which the responses to a single large optic flow patch were contrasted with responses to an array of 9 similar flow patches. This distinguishes cortical regions where neurons respond to flow in their receptive fields regardless of surrounding motion from those that are sensitive to whether the overall image arises from self-motion.

Rehabilitation Approaches in Macular Degeneration Patients.

Age related macular degeneration (AMD) is a visual disease that affects elderly population. It entails a progressive loss of central vision whose consequences are dramatic for the patient's quality of life. Current rehabilitation programs are restricted to technical aids based on visual devices.

Visual straight-ahead preference in saccadic eye movements.

Ocular saccades bringing the gaze toward the straight-ahead direction (centripetal) exhibit higher dynamics than those steering the gaze away (centrifugal). This is generally explained by oculomotor determinants: centripetal saccades are more efficient because they pull the eyes back toward their primary orbital position. However, visual determinants might also be invoked: elements located straight-ahead trigger saccades more efficiently because they receive a privileged visual processing.

The spatial range of peripheral collinear facilitation.

Contrast detection thresholds for a central Gabor patch (target) can be modulated by the presence of co-oriented and collinear high contrast Gabors flankers. In foveal vision collinear facilitation can be observed for target-to-flankers relative distances beyond two times the wavelength (λ) of the Gabor's carrier, while for shorter relative distances (<2λ) there is suppression. These modulatory influences seem to disappear after 12λ.

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 target's detectability.

Privileged visual processing of the straight-ahead direction in humans.

At any moment, the objects we face are endowed with a special behavioral status, either as potential obstacles during navigation or as optimal targets for visually guided actions. Yet, the gaze frequently jumps from one location to another when exploring the visual surroundings, so that objects located straight-ahead are often seen from the corner of the eyes. In the present study, we tested the hypothesis that peripheral vision might nevertheless ensure a privileged processing of these behaviorally important objects.

A PET study of photophobia during spontaneous migraine attacks.

Background: Photophobia is an abnormal sensitivity to light experienced by migraineurs during attacks. The pathophysiology of photophobia is poorly understood. Nevertheless, 2 facts appear to have a link with photophobia: visual cortex hyperexcitability on the one hand and interactions between visual pathway and trigeminal nociception on the other.

Photophobia in migraine: an interictal PET study of cortical hyperexcitability and its modulation by pain.

Objective: Photophobia is an abnormal sensitivity to light experienced by migraineurs and is perhaps caused by cortical hyperexcitability. In clinical studies, an inter-relation between light perception and trigeminal nociception has been demonstrated in migraineurs but not in controls. The purpose of the study was to verify this interaction by functional imaging.

Privileged processing of the straight-ahead direction in primate area V1.

Gaze direction modulates the gain of neurons in most of the visual cortex, including the primary visual (V1) area. These gain modulations are thought to support a mechanism involved in the spatial localization of objects. In the present study, we show that part of them may reflect an additional function: enhancing the visual processing of the objects located straight ahead.

Neural correlates of chromostereopsis: an evoked potential study.

Chromostereopsis is an illusion of depth arising from colour contrast: ocular chromatic aberrations usually make red appear closer to the viewer than blue. Whereas this phenomenon is widely documented from the optical and psychophysical point of view, its neural correlates have not been investigated. To determine the cortical processing of this colour-based depth effect, visual evoked potentials (VEPs) to contrasts of colour were recorded in 25 subjects.

Visuo-auditory interactions in the primary visual cortex of the behaving monkey: electrophysiological evidence.

Background: Visual, tactile and auditory information is processed from the periphery to the cortical level through separate channels that target primary sensory cortices, from which it is further distributed to functionally specialized areas. Multisensory integration is classically assigned to higher hierarchical cortical areas, but there is growing electrophysiological evidence in man and monkey of multimodal interactions in areas thought to be unimodal, interactions that can occur at very short latencies. Such fast timing of multisensory interactions rules out the possibility of an origin in the polymodal areas mediated through back projections, but is rather in favor of heteromodal connections such as the direct projections observed in the monkey, from auditory areas (including the primary auditory cortex AI) directly to the primary visual cortex V1.

Neural bases of stereopsis across visual field of the alert macaque monkey.

Left and right retinal images of an object seen by the 2 eyes can occupy slightly disparate horizontal and/or vertical locations. The role of horizontal disparity (HD) in stereoscopic vision is well established, but the functional contribution of vertical disparity (VD) remains unclear. Various psychophysical studies have shown that HD and VD are used differently by the visual system depending on their location in the visual field, whether near the center of gaze or more peripheral.

At what stage of neural processing do perspective depth cues make a difference?

The present study investigated the cortical processing of three-dimensional (3D) perspective cues in humans, to determine how the brain computes depth from a bidimensional retinal image. We recorded visual evoked potentials in 12 subjects in response to flat and in-perspective stimuli, which evoked biphasic potentials over posterior electrodes. The first, positive component (P1, at 90 ms) was not sensitive to perspective, while the second, negative peak (N1 at approximately 150 ms) was significantly larger for 3D stimuli, regardless of attention.