Development of contrast normalization mechanisms during childhood and adolescence.

Contrast sensitivity is regulated by neural mechanisms that flexibly adjust responsiveness to optimize stimulus encoding across different environments. Here we studied the developmental status of gain control mechanisms in school-age children (5-17years) and adults using a visual masking paradigm. A variable contrast, spatially random 2-D noise test pattern was masked by the presence of a superimposed independent noise pattern presented at 0, 12 and 40% contrast.

Electrophysiological measures of low-level vision reveal spatial processing deficits and hemispheric asymmetry in autism spectrum disorder.

There is accumulating evidence from electrophysiological studies that low-level visual processing is atypical in individuals with autism spectrum disorders (ASDs). Abnormalities in early stages of sensory processing are of interest because they could lead to downstream functional deficits in social or cognitive domains. Using steady-state visual evoked potentials (SSVEPs), we studied how well spatial information is transmitted over a wide range of spatial frequencies (2-30 cycles/deg), including those at the limit of visibility (visual acuity).

The assessment of subjective visual vertical: comparison of two psychophysical paradigms and age-related performance.

Perception of the subjective visual vertical (SVV) is usually assessed by asking to subjects, in complete darkness, to adjust the position of a luminous rod that is variably tilted (i.e., by the method of adjustment [ADJ]).

Spatiotemporal dynamics of perisaccadic remapping in humans revealed by classification images.

We actively scan our environment with fast ballistic movements called saccades, which create large and rapid displacements of the image on the retina. At the time of saccades, vision becomes transiently distorted in many ways: Briefly flashed stimuli are displaced in space and in time, and spatial and temporal intervals appear compressed. Here we apply the psychophysical technique of classification images to study the spatiotemporal dynamics of visual mechanisms during saccades.

Spatio-temporal templates of transient attention revealed by classification images.

Visual attention is captured by transient signals in the periphery of the visual field, allowing enhanced perceptual representations in spatial tasks. However, it has been reported that the same cues impair performance in temporal tasks (e.g.

The subjective visual vertical in patients with pusher behaviour: a pilot study with a psychophysical approach.

Pusher behaviour (PB) reflects some misrepresentation of verticality. However, its neural mechanisms are still unclear. The aim of this pilot study is to assess the perception of the subjective visual vertical in patients with PB using an orientation discrimination task relying on a psychophysical forced-choice procedure.

Acoustic cues to visual detection: a classification image study.

A non-informative sound is known to improve contrast detection thresholds for a synchronous visual target (M. Lippert, N. K.

Reward sharpens orientation coding independently of attention.

It has long been known that rewarding improves performance. However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs? Some recent studies suggest that primary sensory areas, including V1 and A1, may form part of the circuitry of reward-based modulations, but there is no data indicating whether reward can be dissociated from attention or cross-trial forms of perceptual learning. Here we address this issue with a psychophysical dual task, to control attention, while perceptual performance on oriented targets associated with different levels of reward is assessed by measuring both orientation discrimination thresholds and behavioral tuning functions for tilt values near threshold.

Alpha waves: a neural signature of visual suppression.

Alpha waves are traditionally considered a passive consequence of the lack of stimulation of sensory areas. However, recent results have challenged this view by showing a modulation of alpha activity in cortical areas representing unattended information during active tasks. These data have led us to think that alpha waves would support a 'gating function' on sensorial stimulation that actively inhibits unattended information in attentional tasks.

Reported quality of randomized controlled trials in neglect rehabilitation.

The aim of this study is to assess the reported quality of randomized controlled trials (RCTs) on the effectiveness of neglect rehabilitation using a standardized scale. A search of seven electronic databases was carried out. Selected articles were scored using the PEDro scale and classified as high or low quality study both with the original cut off of 6 and a modified cut off of 5.

Search superiority in autism within, but not outside the crowding regime.

Visual cognition of observers with autism spectrum disorder (ASD) seems to show an unbalance between the complementary functions of integration and segregation. This study uses visual search and crowding paradigms to probe the relative ability of children with autism, compared to normal developments children, to extract individual targets from cluttered backgrounds both within and outside the crowding regime. The data show that standard search follows the same pattern in the ASD and control groups with a strong effect of the set size that is substantially weakened by cueing the target location with a synchronous spatial cue.

Neural correlates of texture and contour integration in children with autism spectrum disorders.

In this study, we have used an electrophysiological paradigm to investigate the neural correlates of the visual integration of local signals across space to generate global percepts in a group of low functioning autistic kids. We have analyzed the amplitude of key harmonics of the Visual Evoked Potentials (VEPs) recorded while participants observed orientation-based texture and contour stimuli, forming coherent global patterns, alternating with visual patterns in which the same number of local elements were randomly oriented in order to loose any globally organized feature. Comparing the results of the clinical sample with those obtained in an age-matched control group, we have observed that in the texture conditions the 1st and 3rd harmonics, containing signature of global form processing (Norcia, Pei, Bonneh, Hou, Sampath, & Pettet, 2005), were present in the control group, while in the experimental group only the 1st harmonic was present.

Pooling and segmenting motion signals.

Humans are extremely sensitive to visual motion, largely because local motion signals can be integrated over a large spatial region. On the other hand, summation is often not advantageous, for example when segmenting a moving stimulus against a stationary or oppositely moving background. In this study we show that the spatial extent of motion integration is not compulsory, but is subject to voluntary attentional control.

Non-linear integration of crowded orientation signals.

Crowding of oriented signals has been explained as linear, compulsory averaging of the signals from target and flankers [Parkes, L., Lund, J., Angelucci, A.

Visual clutter causes high-magnitude errors.

Perceptual decisions are often made in cluttered environments, where a target may be confounded with competing "distractor" stimuli. Although many studies and theoretical treatments have highlighted the effect of distractors on performance, it remains unclear how they affect the quality of perceptual decisions. Here we show that perceptual clutter leads not only to an increase in judgment errors, but also to an increase in perceived signal strength and decision confidence on erroneous trials.

Attention to locations and features: different top-down modulation of detector weights.

It is well known that attention improves the visibility of a target. In this study, we examined the effect of attention on the selectivity profile for a target. We used a masking technique to measure the tuning function for detecting a target while cueing either its orientation or its location.

"Pop-out" of targets modulated in luminance or colour: the effect of intrinsic and extrinsic uncertainty.

Targets defined by attributes such as colour or brightness are said to "pop-out" from a cluttered scene, with little or no dependency on the size of the set to be searched, while search for other attributes can depend strongly on set-size. We measured contrast thresholds for increments and decrements in luminance or colour and show that they increase strongly with set-size (as previously observed for orientation). However, in some conditions, where the potential distractors were not salient visual targets, there was no dependency of set-size at all ("pop-out").

Comparing integration rules in visual search.

Search performance for a target tilted in a known direction among vertical distractors is well explained by signal detection theory models. Typically these models use a maximum-of-outputs rule (Max rule) to predict search performance. The Max rule bases its decision on the largest response from a set of independent noisy detectors.