Cortical Surround Interactions and Perceptual Salience via Natural Scene Statistics

Spatial context in images induces perceptual phenomena associated with salience and modulates the responses of neurons in primary visual cortex (V1). However, the computational and ecological principles underlying contextual effects are incompletely understood. We introduce a model of natural images that includes grouping and segmentation of neighboring features based on their joint statistics, and we interpret the firing rates of V1 neurons as performing optimal recognition in this model. We show that this leads to a substantial generalization of divisive normalization, a computation that is ubiquitous in many neural areas and systems. A main novelty in our model is that the influence of the context on a target stimulus is determined by their degree of statistical dependence. We optimized the parameters of the model on natural image patches, and then simulated neural and perceptual responses on stimuli used in classical experiments. The model reproduces some rich and complex response patterns observed in V1, such as the contrast dependence, orientation tuning and spatial asymmetry of surround suppression, while also allowing for surround facilitation under conditions of weak stimulation. It also mimics the perceptual salience produced by simple displays, and leads to readily testable predictions. Our results provide a principled account of orientation-based contextual modulation in early vision and its sensitivity to the homogeneity and spatial arrangement of inputs, and lends statistical support to the theory that V1 computes visual salience

Graphene-Enabled Optoelectronics on Paper

The realization of optoelectronic devices on paper has been an outstanding challenge due to the large surface roughness and incompatible nature of paper with optical materials. Here, we demonstrate a new class of optoelectronic devices on a piece of printing paper using graphene as an electrically reconfigurable optical medium. Our approach relies on electro-modulation of optical properties of multilayer graphene on paper via blocking the interband electronic transitions. The paper based devices yield high optical contrast in the visible spectrum with a fast response. Pattering graphene into multiple pixels, folding paper into three-dimensional shapes or printing colored ink on paper substrates enable us to demonstrate novel optoelectronic devices which cannot be realized with wafer-based techniques

Synthesis of Large Area Graphene for High Performance in Flexible Optoelectronic Devices

This work demonstrates an attractive low-cost route to obtain large area and high-quality graphene films by using the ultra-smooth copper foils which are typically used as the negative electrodes in lithium-ion batteries. We first compared the electronic transport properties of our new graphene film with the one synthesized by using commonly used standard copper foils in chemical vapor deposition (CVD). We observed a stark improvement in the electrical performance of the transistors realized on our graphene films. To study the optical properties on large area, we transferred CVD based graphene to transparent flexible substrates using hot lamination method and performed large area optical scanning. We demonstrate the promise of our high quality graphene films for large areas with ∼400 cm 2 flexible optical modulators. We obtained a profound light modulation over a broad spectrum by using the fabricated large area transparent graphene supercapacitors and we compared the performance of our devices with the one based on graphene from standard copper. We propose that the copper foils used in the lithium-ion batteries could be used to obtain high-quality graphene at much lower-cost, with the improved performance of electrical transport and optical properties in the devices made from them

Valvular surgery in Behcet's disease

Background: Behcet's disease is a chronic inflammatory disease with a relapsing course. Behcet's disease affects many systems and causes hypercoagulability, and detection of an intracardiac mass in a Behcet patient should raise the question of an intracardiac thrombus. We analyzed our patients with Behcet's disease operated for valvular disease. Methods: We operated three patients (one male and two females) who had been diagnosed as having Behcet's disease previously. Using mechanical bileaflet valves, aortic valve replacement in two and mitral valve replacement in the other patient were performed. Mechanical valve replacement was performed using pledgetted-interrupted sutures in the mitral procedure. Patients' steroid therapies were not interrupted and in the postoperative course, steroid was continued. No reoperations were needed. Anticoagulation with warfarin was instituted after the operation with the target of an international normalized ratio (INR) between 3 and 3.5. Results:There was no mortality either early or late follow-up. Intraoperative and postoperative courses were uneventful. Two had ventricular arrhythmias. Total follow-up was 23.3 patient/years with a mean of 93.3 +/- 64.7 months. In the late follow-up, patient with the mechanical mitral valve experienced a cerebrovascular accident 40 months after the operation. Her echocardiographic examination gave a functional valve without any pathology. Conclusions:Surgeons should remember the hypercoagulable state in Behcet patients and strict anticoagulation protocols should be utilized. In the operations, bileaflet prostheses should be used

Noise and the Perceptual Filling-in effect

Nearby collinear flankers increase the false alarm rate (reports of the target being present when it is not) in a Yes-No experiment. This effect has been attributed to “filling-in” of the target location due to increased activity induced by the flankers. According to signal detection theory, false alarms are attributed to noise in the visual nervous system. Here we investigated the effect of external noise on the filling-in effect by adding white noise to a low contrast Gabor target presented between two collinear Gabor flankers at a range of target-flanker separations. External noise modulates the filling-in effect, reducing visual sensitivity (d′) and increasing the filling-in effect (False Alarm rate). We estimated the amount of external noise at which the false alarm rate increases by the √2 (which we refer to as N(FA)). Across flank distances, both the false alarm rate and d′ (with no external noise) are correlated with N(FA). These results are consistent with the notion that nearby collinear flankers add both signal and noise to the target location. The increased signal results in higher d′ values; the increased noise to higher false alarm rates (the filling effect)