Are v1 simple cells optimized for visual occlusions? : A comparative study

Abstract: Simple cells in primary visual cortex were famously found to respond to low-level image components such as edges. Sparse coding and independent component analysis (ICA) emerged as the standard computational models for simple cell coding because they linked their receptive fields to the statistics of visual stimuli. However, a salient feature of image statistics, occlusions of image components, is not considered by these models. Here we ask if occlusions have an effect on the predicted shapes of simple cell receptive fields. We use a comparative approach to answer this question and investigate two models for simple cells: a standard linear model and an occlusive model. For both models we simultaneously estimate optimal receptive fields, sparsity and stimulus noise. The two models are identical except for their component superposition assumption. We find the image encoding and receptive fields predicted by the models to differ significantly. While both models predict many Gabor-like fields, the occlusive model predicts a much sparser encoding and high percentages of ‘globular’ receptive fields. This relatively new center-surround type of simple cell response is observed since reverse correlation is used in experimental studies. While high percentages of ‘globular’ fields can be obtained using specific choices of sparsity and overcompleteness in linear sparse coding, no or only low proportions are reported in the vast majority of studies on linear models (including all ICA models). Likewise, for the here investigated linear model and optimal sparsity, only low proportions of ‘globular’ fields are observed. In comparison, the occlusive model robustly infers high proportions and can match the experimentally observed high proportions of ‘globular’ fields well. Our computational study, therefore, suggests that ‘globular’ fields may be evidence for an optimal encoding of visual occlusions in primary visual cortex. Author Summary: The statistics of our visual world is dominated by occlusions. Almost every image processed by our brain consists of mutually occluding objects, animals and plants. Our visual cortex is optimized through evolution and throughout our lifespan for such stimuli. Yet, the standard computational models of primary visual processing do not consider occlusions. In this study, we ask what effects visual occlusions may have on predicted response properties of simple cells which are the first cortical processing units for images. Our results suggest that recently observed differences between experiments and predictions of the standard simple cell models can be attributed to occlusions. The most significant consequence of occlusions is the prediction of many cells sensitive to center-surround stimuli. Experimentally, large quantities of such cells are observed since new techniques (reverse correlation) are used. Without occlusions, they are only obtained for specific settings and none of the seminal studies (sparse coding, ICA) predicted such fields. In contrast, the new type of response naturally emerges as soon as occlusions are considered. In comparison with recent in vivo experiments we find that occlusive models are consistent with the high percentages of center-surround simple cells observed in macaque monkeys, ferrets and mice

The Importance of Hydration in Wound Healing: Reinvigorating the clinical perspective

Balancing skin hydration levels is important as any disruption in skin integrity will result in disturbance of the dermal water balance. The discovery that a moist wound healing environment actively supports the healing response when compared to a dry environment highlights the importance of water and good hydration levels for optimal wound healing. The benefits of “wet” or “hyper-hydrated” wound healing appears to offer benefits that are similar to those offered by moist wound healing over wounds healing in a dry environment. This suggests that the presence of free water itself during wound healing may not be detrimental to healing but that any adverse effects of wound fluid on tissues is more likely related to the biological components contained within chronic wound exudate (e.g. elevated protease levels). Appropriate dressings applied to wounds must be able to absorb not only the exudate but also retain this excess fluid together with its protease solutes while concurrently preventing desiccation. This is particularly important in the case of chronic wounds where peri-wound skin barrier properties are compromised and there is increased permeation across the injured skin barrier. This review discusses the importance of appropriate levels of hydration in skin with a particular focus on the need for optimal hydration levels for effective healing

Investigation of test methods, material properties and processes for solar cell encapsulants

The goal of the program is to identify, test, evaluate and recommend encapsulation materials and processes for the fabrication of cost-effective and long life solar modules. Of the $18 (1948$) per square meter allocated for the encapsulation components approximately 50% of the cost ($9/sq m) may be taken by the load bearing component. Due to the proportionally high cost of this element, lower costing materials were investigated. Wood based products were found to be the lowest costing structural materials for module construction, however, they require protection from rainwater and humidity in order to acquire dimensional stability. The cost of a wood product based substrate must, therefore, include raw material costs plus the cost of additional processing to impart hygroscopic inertness. This protection is provided by a two step, or split process in which a flexible laminate containing the cell string is prepared, first in a vacuum process and then adhesively attached with a back cover film to the hardboard in a subsequent step

Ultrasonic Doppler measurement of renal artery blood flow

Studies were made of (1) blood flow redistribution during lower body negative pressure (LBNP), (2) the profile of blood flow across the mitral annulus of the heart (both perpendicular and parallel to the commissures), (3) testing and evaluation of a number of pulsed Doppler systems, (4) acute calibration of perivascular Doppler transducers, (5) redesign of the mitral flow transducers to improve reliability and ease of construction, and (6) a frequency offset generator designed for use in distinguishing forward and reverse components of blood flow by producing frequencies above and below the offset frequency. Finally methodology was developed and initial results were obtained from a computer analysis of time-varying Doppler spectra

Impregnant formulation to the preservation, protection and consolidation of wood heritage assets

The protection of cultural heritage is an integral part of the world´s material wealth. The cultural heritage, movable and immovable, together with the natural environment, represents values that contribute to the education and social culture of the community. It also has a significant economic impact because, it represents the basic prerequisite for a tourism industry. Therefore, the modern developing based on non-polluting technological products for the protection of patrimonial is needed. Also, it is necessary to build a bridge between the basic knowledge generated as a product of scientific research and applied science. The knowing of what kind of deterioration occurs and how it impacts the physical-mechanical properties of the materials are important issues and, that must be considered so that the constructions made can be adequately conserved and/or consolidated. Wood was treated with an innovate formulation based on silanes (methyltriethoxysilane, MTES and noctyltryethoxysilane, OTES) to achieve the protection and the consolidation of the heritage assets. The performance of treatment about dimensional stability, fire and biodeterioration/biodegradation resistance was investigated. It was concluded that the treatment resulted effective as a protective and consolidate lasur system based on silanes by surface treatment for wood heritage assets.Fil: Alfieri, Paula Vanesa. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; ArgentinaFil: Lofeudo, Rosana. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; ArgentinaFil: Canosa, Guadalupe. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina. Universidad Tecnológica Nacional; Argentin

Appraisal of patient-reported outcome measures in analogous diseases and recommendations for use in phase II and III clinical trials of pyruvate kinase deficiency

Purpose: Pyruvate kinase deficiency (PKD) is a rare disease and understanding of its epidemiology and associated burden remains limited. With no current curative therapy, clinical manifestations can be life threatening, clinically managed by maintaining adequate hemoglobin levels through transfusion and subsequent support, but with frequent complications. Treatment goals are to maintain/improve the patient’s quality of life. With new therapies, reliable, valid, and relevant patient-reported outcome (PRO) tools are required for use in clinical trials. Methods: Systematic literature search identified no current PRO tools for capturing/measuring the impact of PKD and treatments in clinical trials. Therefore, the search strategy was revised to consider conditions analogous to PKD in terms of symptoms and impacts that might serve as parallels to the experience in PKD; this included sickle cell anemia, thalassemia, and hemolytic anemia. Psychometric properties, strengths, and weakness of selected appropriate PRO instruments were compared, and recommendations made for choice of PRO tools. Results: In adult populations, EORTC QLQ C30 and SF-36v2 are recommended, the former being a basic minimum, covering generic HRQoL, and core symptoms such as fatigue. In pediatric populations, PedsQL Generic Core Scale to measure HRQoL and PedsQL MFS scale to measure fatigue are recommended. Conclusions: Some symptoms/life impacts may be unique to PKD and not observable in analogous conditions. A ‘Physico-Psychosocial Model’ derived from the ‘Medical Model’ is proposed to form the basis for a hypothesized conceptual framework to address the development of PKD-specific PRO instruments.Peer reviewedFinal Published versio

Hybrid Equation/Agent-Based Model of Ischemia-Induced Hyperemia and Pressure Ulcer Formation Predicts Greater Propensity to Ulcerate in Subjects with Spinal Cord Injury

Pressure ulcers are costly and life-threatening complications for people with spinal cord injury (SCI). People with SCI also exhibit differential blood flow properties in non-ulcerated skin. We hypothesized that a computer simulation of the pressure ulcer formation process, informed by data regarding skin blood flow and reactive hyperemia in response to pressure, could provide insights into the pathogenesis and effective treatment of post-SCI pressure ulcers. Agent-Based Models (ABM) are useful in settings such as pressure ulcers, in which spatial realism is important. Ordinary Differential Equation-based (ODE) models are useful when modeling physiological phenomena such as reactive hyperemia. Accordingly, we constructed a hybrid model that combines ODEs related to blood flow along with an ABM of skin injury, inflammation, and ulcer formation. The relationship between pressure and the course of ulcer formation, as well as several other important characteristic patterns of pressure ulcer formation, was demonstrated in this model. The ODE portion of this model was calibrated to data related to blood flow following experimental pressure responses in non-injured human subjects or to data from people with SCI. This model predicted a higher propensity to form ulcers in response to pressure in people with SCI vs. non-injured control subjects, and thus may serve as novel diagnostic platform for post-SCI ulcer formation. © 2013 Solovyev et al