Accurate depth-color scene modeling for 3D contents generation with low cost depth cameras

In this paper, we present a depth-color scene modeling strategy for indoors 3D contents generation. It combines depth and visual information provided by a low-cost active depth camera to improve the accuracy of the acquired depth maps considering the different dynamic nature of the scene elements. Accurate depth and color models of the scene background are iteratively built, and used to detect moving elements in the scene. The acquired depth data is continuously processed with an innovative joint-bilateral filter that efficiently combines depth and visual information thanks to the analysis of an edge-uncertainty map and the detected foreground regions. The main advantages of the proposed approach are: removing depth maps spatial noise and temporal random fluctuations; refining depth data at object boundaries, generating iteratively a robust depth and color background model and an accurate moving object silhouette.

Desarrollo de un proceso de razonamiento visual para la valoración del patrimonio

El tema de la presente tesis es la valoración del patrimonio y en ella se considera que el patrimonio es un proceso cultural interesado en negociar, crear y recrear recuerdos, valores y significados culturales. Actualmente el patrimonio como proceso se está consolidando en la literatura científica, aunque la idea de que es una ‘cosa’ es dominante en el debate internacional y está respaldada tanto por políticas como prácticas de la UNESCO. El considerar el patrimonio como un proceso permite una mirada crítica, que subraya la significación. Es decir, supone el correlato que conlleva definir algo como ‘patrimonio’, o hacer que lo vaya siendo. Esta visión del concepto permite la posibilidad de comprender no sólo lo que se ha valorado, sino también lo que se ha olvidado y el porqué. El principal objetivo de esta investigación es explorar las características de un proceso de razonamiento visual para aplicarlo en el de valoración del patrimonio. Éste que se presenta, implica la creación de representaciones visuales y sus relaciones, además su meta no está centrada en producir un ambiente que sea indiferenciado de la realidad física. Con él se pretende ofrecer la posibilidad de comunicar la dimensión ‘poliédrica’ del patrimonio. Para que este nuevo proceso que propongo sea viable y sostenible, existe la necesidad de tener en cuenta el fin que se quiere lograr: la valoración. Es importante considerar que es un proceso en el cual las dinámicas de aprendizaje, comportamientos y exploración del patrimonio están directamente relacionadas con su valoración. Por lo tanto, hay que saber cómo se genera la valoración del patrimonio, con el fin de ser capaces de desarrollar el proceso adaptado a estas dinámicas. La hipótesis de esta tesis defiende que un proceso de razonamiento visual para la valoración del patrimonio permite que las personas involucradas en el proceso inicien un proceso de interacción con un elemento patrimonial y su imagen mental para llegar a ciertas conclusiones con respecto a su valor y significado. El trabajo describe la metodología que da lugar al proceso de razonamiento visual para el patrimonio, que ha sido concebido sobre un modelado descriptivo de procesos, donde se han caracterizado tres niveles: meta-nivel, de análisis y operacional. En el modelado del proceso los agentes, junto con el patrimonio, son los protagonistas. El enfoque propuesto no es sólo sobre el patrimonio, sino sobre la compleja relación entre las personas y el patrimonio. Los agentes humanos dan valor a los testimonios de la vida pasada y les imbuyen de significado. Por lo tanto, este enfoque de un proceso de razonamiento visual sirve para detectar los cambios en el valor del patrimonio, además de su dimensión poliédrica en términos espaciales y temporales. Además se ha propuesto una nueva tipología de patrimonio necesaria para sustentar un proceso de razonamiento visual para su valoración. Esta tipología está apoyada en la usabilidad del patrimonio y dentro de ella se encuentran los siguientes tipos de patrimonio: accesible, cautivo, contextualizado, descontextualizado, original y vicarial. El desarrollo de un proceso de razonamiento visual para el patrimonio es una propuesta innovadora porque integra el proceso para su valoración, contemplando la dimensión poliédrica del patrimonio y explotando la potencialidad del razonamiento visual. Además, los posibles usuarios del proceso propuesto van a tener interacción de manera directa con el patrimonio e indirecta con la información relativa a él, como por ejemplo, con los metadatos. Por tanto, el proceso propuesto posibilita que los posibles usuarios se impliquen activamente en la propia valoración del patrimonio. ABSTRACT The subject of this thesis is heritage valuation and it argues that heritage is a cultural process that is inherited, transmitted, and transformed by individuals who are interested in negotiating, creating and recreating memories and cultural meanings. Recently heritage as a process has seen a consolidation in the research, although the idea that heritage is a ‘thing’ is dominant in the international debate and is supported by policies and practice of UNESCO. Seeing heritage as a process enables a critical view, underscoring the significance. That is, it is the correlate involved in defining something as ‘heritage’, or converting it into heritage. This view of the concept allows the possibility to understand not only what has been valued, but also what has been forgotten and why. The main objective of this research is to explore the characteristics of a visual reasoning process in order to apply it to a heritage valuation. The goal of the process is not centered on producing an environment that is undifferentiated from physical reality. Thus, the objective of the process is to provide the ability to communicate the ‘polyhedral’ dimension of heritage. For this new process to be viable and sustainable, it is necessary to consider what is to be achieved: heritage valuation. It is important to note that it is a process in which the dynamics of learning, behavior and exploration heritage are directly related to its valuation. Therefore, we need to know how this valuation takes place in order to be able to develop a process that is adapted to these dynamic. The hypothesis of this thesis argues that a visual reasoning process for heritage valuation allows people involved in the process to initiate an interaction with a heritage and to build its mental image to reach certain conclusions regarding its value and meaning. The thesis describes the methodology that results in a visual reasoning process for heritage valuation, which has been based on a descriptive modeling process and have characterized three levels: meta, analysis and operational -level. The agents are the protagonists in the process, along with heritage. The proposed approach is not only about heritage but the complex relationship between people and heritage. Human operators give value to the testimonies of past life and imbue them with meaning. Therefore, this approach of a visual reasoning process is used to detect changes in the value of heritage and its multifaceted dimension in spatial and temporal terms. A new type of heritage required to support a visual reasoning process for heritage valuation has also been proposed. This type is supported by its usability and it covers the following types of heritage: available, captive, contextualized, decontextualized, original and vicarious. The development of a visual reasoning process for heritage valuation is innovative because it integrates the process for valuation of heritage, considering the multifaceted dimension of heritage and exploiting the potential of visual reasoning. In addition, potential users of the proposed process will have direct interaction with heritage and indirectly with the information about it, such as the metadata. Therefore, the proposed process enables potential users to be actively involved in their own heritage valuation.

Statistical Multi-Objective Structural Damage Identification based on Dynamic Parameters

Evolutionary algorithms are suitable to solve damage identification problems in a multi-objective context. However, the performance of these methods can deteriorate quickly with increasing noise intensities originating numerous uncertainties. In this paper, a statistic structural damage detection method formulated in a multi-objective context is proposed. The statistic analysis is implemented to take into account the uncertainties existing in the structural model and measured structural modal parameters. The presented method is verified by a number of simulated damage scenarios. The effects of noise and damage levels on damage detection are investigated.

Color uniformity in spotligths - visual perception and system design

La iluminación con diodos emisores de luz (LED) está reemplazando cada vez en mayor medida a las fuentes de luz tradicionales. La iluminación LED ofrece ventajas en eficiencia, consumo de energía, diseño, tamaño y calidad de la luz. Durante más de 50 años, los investigadores han estado trabajando en mejoras LED. Su principal relevancia para la iluminación está aumentando rápidamente. Esta tesis se centra en un campo de aplicación importante, como son los focos. Se utilizan para enfocar la luz en áreas definidas, en objetos sobresalientes en condiciones profesionales. Esta iluminación de alto rendimiento requiere una calidad de luz definida, que incluya temperaturas ajustables de color correlacionadas (CCT), de alto índice de reproducción cromática (CRI), altas eficiencias, y colores vivos y brillantes. En el paquete LED varios chips de diferentes colores (rojo, azul, fósforo convertido) se combinan para cumplir con la distribución de energía espectral con alto CRI. Para colimar la luz en los puntos concretos deseados con un ángulo de emisión determinado, se utilizan blancos sintonizables y diversos colores de luz y ópticas secundarias. La combinación de una fuente LED de varios colores con elementos ópticos puede causar falta de homogeneidad cromática en la distribución espacial y angular de la luz, que debe resolverse en el diseño óptico. Sin embargo, no hay necesidad de uniformidad perfecta en el punto de luz debido al umbral en la percepción visual del ojo humano. Por lo tanto, se requiere una descripción matemática del nivel de uniformidad del color con respecto a la percepción visual. Esta tesis está organizada en siete capítulos. Después de un capítulo inicial que presenta la motivación que ha guiado la investigación de esta tesis, en el capítulo 2 se presentan los fundamentos científicos de la uniformidad del color en luces concentradas, como son: el espacio de color aplicado CIELAB, la percepción visual del color, los fundamentos de diseño de focos respecto a los motores de luz y ópticas no formadoras de imágenes, y los últimos avances en la evaluación de la uniformidad del color en el campo de los focos. El capítulo 3 desarrolla diferentes métodos para la descripción matemática de la distribución espacial del color en un área definida, como son la diferencia de color máxima, la desviación media del color, el gradiente de la distribución espacial de color, así como la suavidad radial y axial. Cada función se refiere a los diferentes factores que influyen en la visión, los cuales necesitan un tratamiento distinto que el de los datos que se tendrán en cuenta, además de funciones de ponderación que pre- y post-procesan los datos simulados o medidos para la reducción del ruido, la luminancia de corte, la aplicación de la ponderación de luminancia, la función de sensibilidad de contraste, y la función de distribución acumulativa. En el capítulo 4, se obtiene la función de mérito Usl para la estimación de la uniformidad del color percibida en focos. Se basó en los resultados de dos conjuntos de experimentos con factor humano realizados para evaluar la percepción visual de los sujetos de los patrones de focos típicos. El primer experimento con factor humano dio lugar al orden de importancia percibida de los focos. El orden de rango percibido se utilizó para correlacionar las descripciones matemáticas de las funciones básicas y la función ponderada sobre la distribución espacial del color, que condujo a la función Usl. El segundo experimento con factor humano probó la percepción de los focos bajo condiciones ambientales diversas, con el objetivo de proporcionar una escala absoluta para Usl, para poder así sustituir la opinión subjetiva personal de los individuos por una función de mérito estandarizada. La validación de la función Usl se presenta en relación con el alcance de la aplicación y condiciones, así como las limitaciones y restricciones que se realizan en el capítulo 5. Se compararon los datos medidos y simulados de varios sistemas ópticos. Se discuten los campos de aplicación , así como validaciones y restricciones de la función. El capítulo 6 presenta el diseño del sistema de focos y su optimización. Una evaluación muestra el análisis de sistemas basados en el reflector y la lente TIR. Los sistemas ópticos simulados se comparan en la uniformidad del color Usl, sensibilidad a las sombras coloreadas, eficiencia e intensidad luminosa máxima. Se ha comprobado que no hay un sistema único que obtenga los mejores resultados en todas las categorías, y que una excelente uniformidad de color se pudo alcanzar por la conjunción de dos sistemas diferentes. Finalmente, el capítulo 7 presenta el resumen de esta tesis y la perspectiva para investigar otros aspectos. ABSTRACT Illumination with light-emitting diodes (LED) is more and more replacing traditional light sources. They provide advantages in efficiency, energy consumption, design, size and light quality. For more than 50 years, researchers have been working on LED improvements. Their main relevance for illumination is rapidly increasing. This thesis is focused on one important field of application which are spotlights. They are used to focus light on defined areas, outstanding objects in professional conditions. This high performance illumination required a defined light quality including tunable correlated color temperatures (CCT), high color rendering index (CRI), high efficiencies and bright, vivid colors. Several differently colored chips (red, blue, phosphor converted) in the LED package are combined to meet spectral power distribution with high CRI, tunable white and several light colors and secondary optics are used to collimate the light into the desired narrow spots with defined angle of emission. The combination of multi-color LED source and optical elements may cause chromatic inhomogeneities in spatial and angular light distribution which needs to solved at the optical design. However, there is no need for perfect uniformity in the spot light due to threshold in visual perception of human eye. Therefore, a mathematical description of color uniformity level with regard to visual perception is required. This thesis is organized seven seven chapters. After an initial one presenting the motivation that has guided the research of this thesis, Chapter 2 introduces the scientific basics of color uniformity in spot lights including: the applied color space CIELAB, the visual color perception, the spotlight design fundamentals with regards to light engines and nonimaging optics, and the state of the art for the evaluation of color uniformity in the far field of spotlights. Chapter 3 develops different methods for mathematical description of spatial color distribution in a defined area, which are the maximum color difference, the average color deviation, the gradient of spatial color distribution as well as the radial and axial smoothness. Each function refers to different visual influencing factors, and they need different handling of data be taken into account, along with weighting functions which pre- and post-process the simulated or measured data for noise reduction, luminance cutoff, the implementation of luminance weighting, contrast sensitivity function, and cumulative distribution function. In chapter 4, the merit function Usl for the estimation of the perceived color uniformity in spotlights is derived. It was based on the results of two sets of human factor experiments performed to evaluate the visual perception of typical spotlight patterns by subjects. The first human factor experiment resulted in the perceived rank order of the spotlights. The perceived rank order was used to correlate the mathematical descriptions of basic functions and weighted function concerning the spatial color distribution, which lead to the Usl function. The second human factor experiment tested the perception of spotlights under varied environmental conditions, with to objective to provide an absolute scale for Usl, so the subjective personal opinion of individuals could be replaced by a standardized merit function. The validation of the Usl function is presented concerning the application range and conditions as well as limitations and restrictions in carried out in chapter 5. Measured and simulated data of various optical several systems were compared. Fields of applications are discussed as well as validations and restrictions of the function. Chapter 6 presents spotlight system design and their optimization. An evaluation shows the analysis of reflector-based and TIR lens systems. The simulated optical systems are compared in color uniformity Usl , sensitivity to colored shadows, efficiency, and peak luminous intensity. It has been found that no single system which performed best in all categories, and that excellent color uniformity could be reached by two different system assemblies. Finally, chapter 7 summarizes the conclusions of the present thesis and an outlook for further investigation topics.

Toward Visual Autonomous Ship Board Landing of a VTOL UAV

In this paper we tackle the problem of landing a helicopter autonomously on a ship deck, using as the main sensor, an on-board colour camera. To create a test-bed, we first adequately simulate the movement of a ship landing platform on the Sea, for different Sea States, for different ships, randomly and realistically enough. We use a commercial parallel robot to get this movement. Once we had this, we developed an accurate and robust computer vision system to measure the pose of the helipad with respect to the on-board camera. To deal with the noise and the possible fails of the computer vision, a state estimator was created. With all of this, we are now able to develop and test a controller that closes the loop and finish the autonomous landing task.

Luz industrial e imagen tecnificada: de Moholy Nagy al C.A.V.S. (Center for Advanced Visual Studies)

El desarrollo de la tecnología de la luz implicará la transformación de la vida social, cultural y económica. Tanto las consideraciones espaciales del Movimiento Moderno, como los efectos producidos por la segunda Guerra Mundial, tendrán efectos visibles en las nuevas configuraciones espaciales y en la relación simbiótica y recíproca que se dará entre ideología y tecnología. La transformación en la comprensión de la articulación espacial, asociada al desarrollo tecnológico, afectará al modo en que este espacio es experimentado y percibido. El espacio expositivo y el espacio escénico se convertirán en laboratorio práctico donde desarrollar y hacer comprensible todo el potencial ilusorio de la luz, la proyección y la imagen, como parámetros modificadores y dinamizadores del espacio arquitectónico. Esta experimentación espacial estará precedida por la investigación y creación conceptual en el mundo plástico, donde los nuevos medios mecánicos serán responsables de la construcción de una nueva mirada moderna mediatizada por los elementos técnicos. La experimentación óptica, a través de la fotografía, el cine, o el movimiento de la luz y su percepción, vinculada a nuevos modos de representación y comunicación, se convertirá en elemento fundamental en la configuración espacial. Este ámbito de experimentación se hará patente en la Escuela de la Bauhaus, de la mano de Gropius, Schlemmer o Moholy Nagy entre otros; tanto en reflexiones teóricas como en el desarrollo de proyectos expositivos, arquitectónicos o teatrales, que evolucionarán en base a la tecnología y la modificación de la relación con el espectador. El espacio expositivo y el espacio escénico se tomarán como oportunidad de investigación espacial y de análisis de los modos de percepción, convirtiéndose en lugares de experimentación básicos para el aprendizaje. El teatro se postula como punto de encuentro entre el arte y la técnica, cobrando especial importancia la intersección con otras disciplinas en la definición espacial. Las múltiples innovaciones técnicas ligadas a los nuevos fundamentos teatrales en la modificación de la relación con la escena, que se producen a principios del siglo XX, tendrán como consecuencia la transformación del espacio en un espacio dinámico, tanto física como perceptivamente, que dará lugar a nuevas concepciones espaciales, muchas de ellas utópicas. La luz, la proyección y la creación de ilusión en base a estímulos visuales y sonoros, aparecen como elementos proyectuales efímeros e inmateriales, que tendrán una gran incidencia en el espacio y su modo de ser experimentado. La implicación de la tecnología en el arte conllevará modificaciones en la visualización, así como en la configuración espacial de los espacios destinados a esta. Destacaremos como propuesta el Teatro Total de Walter Gropius, en cuyo desarrollo se recogen de algún modo las experiencias espaciales y las investigaciones desarrolladas sobre la estructura formal de la percepción realizadas por Moholy Nagy, además de los conceptos acerca del espacio escénico desarrollados en el taller de Teatro de la Bauhaus por Oskar Schlemmer. En el Teatro Total, Gropius incorporará su propia visión de cuestiones que pertenecen a la tradición de la arquitectura teatral y las innovaciones conceptuales que estaban teniendo lugar desde finales del s.XIX, tales como la participación activa del público o la superación entre escena y auditorio, estableciendo en el proyecto una nueva relación perceptual entre sala, espectáculo y espectador; aumentando la sensación de inmersión, a través del uso de la física, la óptica, y la acústica, creando una energía concéntrica capaz de extenderse en todas direcciones. El Teatro Total será uno de los primeros ejemplos en los que desde el punto de partida del proyecto, se conjuga la imagen como elemento comunicativo con la configuración espacial. Las nuevas configuraciones escénicas tendrán como premisa de desarrollo la capacidad de transformación tanto perceptiva, como física. En la segunda mitad del s.XX, la creación de centros de investigación como el CAVS (The Center for Advanced Visual Studies,1967), o el EAT (Experiments in Art and Technology, 1966), favorecerán la colaboración interdisciplinar entre arte y ciencia, implicando a empresas de carácter tecnológico, como Siemens, HP, IBM o Philips, facilitando soporte técnico y económico para el desarrollo de nuevos sistemas. Esta colaboración interdisciplinar dará lugar a una serie de intervenciones espaciales que tendrán su mayor visibilidad en algunas Exposiciones Universales. El resultado será, en la mayoría de los casos, la creación de espacios de carácter inmersivo, donde se establecerá una relación simbiótica entre espacio, imagen, sonido, y espectador. La colocación del espectador en el centro de la escena y la disposición dinámica de imagen y sonido, crearán una particular narrativa espacial no lineal, concebida para la experiencia. Desde las primeras proyecciones de cine a la pantalla múltiple de los Eames, las técnicas espaciales de difusión del sonido en Stockhausen, o los experimentos con el movimiento físico interactivo, la imagen, la luz en movimiento y el sonido, quedan inevitablemente convertidos en material arquitectónico. ABSTRACT. Light technology development would lead to a social, cultural and economic transformation. Both spatial consideration of “Modern Movement” and Second World War effects on technology, would have a visible aftereffect on spatial configuration and on the symbiotic and mutual relationship between ideology & technology. Comprehension adjustment on the articulation of space together with technology development, would impact on how space is perceived and felt. Exhibition space and scenic space would turn into a laboratory where developing and making comprehensive all illusory potential of light, projection and image. These new parameters would modify and revitalize the architectonic space. as modifying and revitalizing parameters of architectonic space. Spatial experimentation would be preceded by conceptual creation and investigation on the sculptural field, where new mechanic media would be responsible for a fresh and modern look influenced by technical elements. Optical experimentation, through photography, cinema or light movement and its perception, would turn into essential components for spatial arrangement linked to new ways of performance and communication. This experimentation sphere would be clear at The Bauhaus School, by the hand of Gropius, Schlemmer or Moholy Nag among others; in theoretical, theatrical or architectural performance’s projects, that would evolve based on technology and also based on the transformation of the relationship with the observer. Exhibition and perfor-mance areas would be taken as opportunities of spatial investigation and for the analysis of the different ways of perception, thus becoming key places for learning. Theater is postulated as a meeting point between art and technique, taking on a new significance at its intersection with other disciplines working with spatial definition too. The multiple innovation techniques linked to the new foundations for the theater regarding stage relation, would have as a consequence the regeneration of the space. Space would turn dynamic, both physically and perceptibly, bringing innovative spatial conceptions, many of them unrealistic. Light, projection and illusory creation based on sound and visual stimulus would appear as intangible and momentary design components, which would have a great impact on the space and on the way it is experienced. Implication of technology in art would bring changes on the observer as well as on the spatial configuration of the art spaces2. It would stand out as a proposal Walter Groupis Total Theater, whose development would include somehow the spatial experiments and studies about formal structure of perception accomplished by Moholy Nagy besides the concepts regarding stage space enhanced at the Bauhaus Theater Studio by Oskar Schlemmer. Within Total Theater, Groupis would incorporate his own view about traditional theatric architecture and conceptual innovations that were taking place since the end of the nineteenth century, such as active audience participation or the diffusing limits between scene and audience, establishing a new perception relationship between auditorium, performance and audience, improving the feeling of immersion through the use of physics, optics and acoustics, creating a concentric energy capable of spreading in all directions. Total Theater would be one of the first example in which, from the beginning of the Project, image is combined as a communicating element with the spatial configuration. As a premise of development, new stage arrangement would have the capacity of transformation, both perceptive and physically. During the second half or the twentieth century, the creation of investigation centers such as CAVS (Center for Advanced Visual Studies, 1967) or EAT (Experiments in Art and Technology, 1966), would help to the interdisciplinary collaboration between art and science, involving technology companies like Siemens, HP, IBM or Philips, providing technical and economic support to the development of new systems. This interdisciplinary collaboration would give room to a series of spatial interventions which would have visibility in some Universal Exhibitions. The result would be, in most cases, the creation of immersive character spaces, where a symbiotic relationship would be stablished between space, image, sound and audience. The new location of the audience in the middle of the display, together with the dynamic arrangement of sound and image would create a particular, no lineal narrative conceived to be experienced. Since the first cinema projections, the multiple screen of Eames, the spatial techniques for sound dissemination at Stockhausen or the interactive physical movement experimentation, image, motion light and sound would turn inevitably into architectural material.

Design and implementation of an adaptive dashboard and visualization interface for the dynamic optimization and control of Data Centers

Over the last few years, the Data Center market has increased exponentially and this tendency continues today. As a direct consequence of this trend, the industry is pushing the development and implementation of different new technologies that would improve the energy consumption efficiency of data centers. An adaptive dashboard would allow the user to monitor the most important parameters of a data center in real time. For that reason, monitoring companies work with IoT big data filtering tools and cloud computing systems to handle the amounts of data obtained from the sensors placed in a data center.Analyzing the market trends in this field we can affirm that the study of predictive algorithms has become an essential area for competitive IT companies. Complex algorithms are used to forecast risk situations based on historical data and warn the user in case of danger. Considering that several different users will interact with this dashboard from IT experts or maintenance staff to accounting managers, it is vital to personalize it automatically. Following that line of though, the dashboard should only show relevant metrics to the user in different formats like overlapped maps or representative graphs among others. These maps will show all the information needed in a visual and easy-to-evaluate way. To sum up, this dashboard will allow the user to visualize and control a wide range of variables. Monitoring essential factors such as average temperature, gradients or hotspots as well as energy and power consumption and savings by rack or building would allow the client to understand how his equipment is behaving, helping him to optimize the energy consumption and efficiency of the racks. It also would help him to prevent possible damages in the equipment with predictive high-tech algorithms.

Bidirectional, experience-dependent regulation of N-methyl-d-aspartate receptor subunit composition in the rat visual cortex during postnatal development

In the visual cortex, as elsewhere, N-methyl-d-aspartate receptors (NMDARs) play a critical role in triggering long-term, experience-dependent synaptic plasticity. Modifications of NMDAR subunit composition alter receptor function, and could have a large impact on the properties of synaptic plasticity. We have used immunoblot analysis to investigate the effects of age and visual experience on the expression of different NMDAR subunits in synaptoneurosomes prepared from rat visual cortices. NMDARs at birth are comprised of NR2B and NR1 subunits, and, over the first 5 postnatal weeks, there is a progressive inclusion of the NR2A subunit. Dark rearing from birth attenuates the developmental increase in NR2A. Levels of NR2A increase rapidly (in <2 hr) when dark-reared animals are exposed to light, and decrease gradually over the course of 3 to 4 days when animals are deprived of light. These data reveal that NMDAR subunit composition in the visual cortex is remarkably dynamic and bidirectionally regulated by sensory experience. We propose that NMDAR subunit regulation is a mechanism for experience-dependent modulation of synaptic plasticity in the visual cortex, and serves to maintain synaptic strength within an optimal dynamic range.

Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting

To investigate the nature of plasticity in the adult visual system, perceptual learning was measured in a peripheral orientation discrimination task with systematically varying amounts of external (environmental) noise. The signal contrasts required to achieve threshold were reduced by a factor or two or more after training at all levels of external noise. The strong quantitative regularities revealed by this novel paradigm ruled out changes in multiplicative internal noise, changes in transducer nonlinearites, and simple attentional tradeoffs. Instead, the regularities specify the mechanisms of perceptual learning at the behavioral level as a combination of external noise exclusion and stimulus enhancement via additive internal noise reduction. The findings also constrain the neural architecture of perceptual learning. Plasticity in the weights between basic visual channels and decision is sufficient to account for perceptual learning without requiring the retuning of visual mechanisms.

Noise in neurons is message dependent

Neuronal responses are conspicuously variable. We focus on one particular aspect of that variability: the precision of action potential timing. We show that for common models of noisy spike generation, elementary considerations imply that such variability is a function of the input, and can be made arbitrarily large or small by a suitable choice of inputs. Our considerations are expected to extend to virtually any mechanism of spike generation, and we illustrate them with data from the visual pathway. Thus, a simplification usually made in the application of information theory to neural processing is violated: noise is not independent of the message. However, we also show the existence of error-correcting topologies, which can achieve better timing reliability than their components.

Receptive field structure in the visual cortex: does selective stimulation induce plasticity?

Sensory areas of adult cerebral cortex can reorganize in response to long-term alterations in patterns of afferent signals. This long-term plasticity is thought to play a crucial role in recovery from injury and in some forms of learning. However, the degree to which sensory representations in primary cortical areas depend on short-term (i.e., minute to minute) stimulus variations remains unclear. A traditional view is that each neuron in the mature cortex has a fixed receptive field structure. An alternative view, with fundamentally different implications for understanding cortical function, is that each cell's receptive field is highly malleable, changing according to the recent history of the sensory environment. Consistent with the latter view, it has been reported that selective stimulation of regions surrounding the receptive field induces a dramatic short-term increase in receptive field size for neurons in the visual cortex [Pettet, M. W. & Gilbert, C. D. (1992) Proc. Natl. Acad. Sci. USA 89, 8366-8370]. In contrast, we report here that there is no change in either the size or the internal structure of the receptive field following several minutes of surround stimulation. However, for some cells, overall responsiveness increases. These results suggest that dynamic alterations of receptive field structure do not underlie short-term plasticity in the mature primary visual cortex. However, some degree of short-term adaptability could be mediated by changes in responsiveness.

Detection of fruit and the selection of primate visual pigments for color vision

Primates have X chromosome genes for cone photopigments with sensitivity maxima from 535 to 562 nm. Old World monkeys and apes (catarrhines) and the New World ( platyrrhine) genus Alouatta have separate genes for 535-nm ( medium wavelength; M) and 562-nm ( long wavelength; L) pigments. These pigments, together with a 425-nm ( short wavelength) pigment, permit trichromatic color vision. Other platyrrhines and prosimians have a single X chromosome gene but often with alleles for two or three M/L photopigments. Consequently, heterozygote females are trichromats, but males and homozygote females are dichromats. The criteria that affect the evolution of M/L alleles and maintain genetic polymorphism remain a puzzle, but selection for finding food may be important. We compare different types of color vision for detecting more than 100 plant species consumed by tamarins ( Saguinus spp.) in Peru. There is evidence that both frequency-dependent selection on homozygotes and heterozygote advantage favor M/L polymorphism and that trichromatic color vision is most advantageous in dim light. Also, whereas the 562-nm allele is present in all species, the occurrence of 535- to 556-nm alleles varies between species. This variation probably arises because trichromatic color vision favors widely separated pigments and equal frequencies of 535/543- and 562-nm alleles, whereas in dichromats, long-wavelength pigment alleles are fitter.

Neuromuscular adaptation during skill acquisition on a two degree-of-freedom target-acquisition task: Dynamic movement

In this experiment, we examined the extent to which the spatiotemporal reorganization of muscle synergies mediates skill acquisition on a two degree-of-freedom (df) target-acquisition task. Eight participants completed five practice sessions on consecutive days. During each session they practiced movements to eight target positions presented by a visual display. The movements required combinations of flexion/extension and pronation/supination of the elbow joint complex. During practice sessions, eight targets displaced 5.4 cm from the start position ( representing joint excursions of 54) were presented 16 times. During pre- and posttests, participants acquired the targets at two distances (3.6 cm [36 degrees] and 7.2 cm [72 degrees]). EMG data were recorded from eight muscles contributing to the movements during the pre- and posttests. Most targets were acquired more rapidly after the practice period. Performance improvements were, in most target directions, accompanied by increases in the smoothness of the movement trajectories. When target acquisition required movement in both dfs, there were also practice-related decreases in the extent to which the trajectories deviated from a direct path to the target. The contribution of monofunctional muscles ( those producing torque in a single df) increased with practice during movements in which they acted as agonists. The activity in bifunctional muscles ( those contributing torque in both dfs) remained at pretest levels in most movements. The results suggest that performance gains were mediated primarily by changes in the spatial organization of muscles synergies. These changes were expressed most prominently in terms of the magnitude of activation of the monofunctional muscles.

Animal visual systems and the evolution of color patterns: Sensory processing illuminates signal evolution

Animal color pattern phenotypes evolve rapidly. What influences their evolution? Because color patterns are used in communication, selection for signal efficacy, relative to the intended receiver's visual system, may explain and predict the direction of evolution. We investigated this in bowerbirds, whose color patterns consist of plumage, bower structure, and ornaments and whose visual displays are presented under predictable visual conditions. We used data on avian vision, environmental conditions, color pattern properties, and an estimate of the bowerbird phylogeny to test hypotheses about evolutionary effects of visual processing. Different components of the color pattern evolve differently. Plumage sexual dimorphism increased and then decreased, while overall (plumage plus bower) visual contrast increased. The use of bowers allows relative crypsis of the bird but increased efficacy of the signal as a whole. Ornaments do not elaborate existing plumage features but instead are innovations (new color schemes) that increase signal efficacy. Isolation between species could be facilitated by plumage but not ornaments, because we observed character displacement only in plumage. Bowerbird color pattern evolution is at least partially predictable from the function of the visual system and from knowledge of different functions of different components of the color patterns. This provides clues to how more constrained visual signaling systems may evolve.

ADSL transceivers applying DSM and their nonstationary noise robustness

Dynamic spectrum management (DSM) comprises a new set of techniques for multiuser power allocation and/or detection in digital subscriber line (DSL) networks. At the Alcatel Research and Innovation Labs, we have recently developed a DSM test bed, which allows the performance of DSM algorithms to be evaluated in practice. With this test bed, we have evaluated the performance of a DSM level-1 algorithm known as iterative water-filling in an ADSL scenario. This paper describes the results of, on the one hand, the performance gains achieved with iterative water-filling, and, on the other hand, the nonstationary noise robustness of DSM-enabled ADSL modems. It will be shown that DSM trades off nonstationary noise robustness for performance improvements. A new bit swap procedure is then introduced to increase the noise robustness when applying DSM.