Time-locked perceptual fading induced by visual transients

After prolonged fixation, a stationary object placed in the peripheral visual field fades and disappears from our visual awareness, especially at low luminance contrast (the Troxler effect). Here, we report that similar fading can be triggered by visual transients, such as additional visual stimuli flashed near the object, apparent motion, or a brief removal of the object itself (blinking). The fading occurs even without prolonged adaptation and is time-locked to the presentation of the visual transients. Experiments show that the effect of a flashed object decreased monotonically as a function of the distance from the target object. Consistent with this result, when apparent motion, consisting of a sequence of flashes was presented between stationary disks, these target disks perceptually disappeared as if erased by the moving object. Blinking the target disk, instead of flashing an additional visual object, turned out to be sufficient to induce the fading. The effect of blinking peaked around a blink duration of 80 msec. Our findings reveal a unique mechanism that controls the visibility of visual objects in a spatially selective and time-locked manner in response to transient visual inputs. Possible mechanisms underlying this phenomenon will be discussed

The CLIC positron production scheme

The CLIC (Compact Linear Collider) positron source is based on the conventional scheme, using a metal converter target and an Adiabatic Matching Device (AMD) composed of a Flux Concentrator (FC) and a constant magnetic field along the positron Pre-Injector linac. The positrons are accelerated with L-band RF structures. Beam dynamics simulations are described for the positron production in the target and capture section in the AMD. The distribution of the energy deposition in the target is studied with the EGS4 code. The dependence of the positron yield on several parameters is studied and optimised using both EGS4 and analytical calculations. Following this optimisation, a new set of design parameters is proposed and particle tracking simulations are performed to estimate the overall performance

Nonstimulated early visual areas carry information about surrounding context

Even within the early sensory areas, the majority of the input to any given cortical neuron comes from other cortical neurons. To extend our knowledge of the contextual information that is transmitted by such lateral and feedback connections, we investigated how visually nonstimulated regions in primary visual cortex (V1) and visual area V2 are influenced by the surrounding context. We used functional magnetic resonance imaging (fMRI) and pattern-classification methods to show that the cortical representation of a nonstimulated quarter-field carries information that can discriminate the surrounding visual context. We show further that the activity patterns in these regions are significantly related to those observed with feed-forward stimulation and that these effects are driven primarily by V1. These results thus demonstrate that visual context strongly influences early visual areas even in the absence of differential feed-forward thalamic stimulation

Oxidative protein folding in the mitochondrial intermembrane space

Disulfide bond formation is a crucial step for oxidative folding and necessary for the acquisition of a protein's native conformation. Introduction of disulfide bonds is catalyzed in specialized subcellular compartments and requires the coordinated action of specific enzymes. The intermembrane space of mitochondria has recently been found to harbor a dedicated machinery that promotes the oxidative folding of substrate proteins by shuttling disulfide bonds. The newly identified oxidative pathway consists of the redox-regulated receptor Mia40 and the sulfhydryl oxidase Erv1. Proteins destined to the intermembrane space are trapped by a disulfide relay mechanism that involves an electron cascade from the incoming substrate to Mia40, then on to Erv1, and finally to molecular oxygen via cytochrome c. This thiol–disulfide exchange mechanism is essential for the import and for maintaining the structural stability of the incoming precursors. In this review we describe the mechanistic parameters that define the interaction and oxidation of the substrate proteins in light of the recent publications in the mitochondrial oxidative folding field