Visual backward masking: Modeling spatial and temporal aspects

In modeling visual backward masking, the focus has been on temporal effects. More specifically, an explanation has been sought as to why strongest masking can occur when the mask is delayed with respect to the target. Although interesting effects of the spatial layout of the mask have been found, only a few attempts have been made to model these phenomena. Here, we elaborate a structurally simple model which employs lateral excitation and inhibition together with different neural time scales to explain many spatial and temporal aspects of backward masking. We argue that for better understanding of visual masking, it is vitally important to consider the interplay of spatial and temporal factors together in one single model

Rio-Konferenz - was war, was bleibt?

Die United Conference on Environment and Development (UNCED) im Juni diesen Jahres in Rio de Janeiro war im Vorfeld mit großen Erwartungen konfrontiert worden, da von ihr wesentliche Verein-barungen und Impulse für die Lösung der globalen Umweltprobleme erwartet worden waren. Nach Abschluß der Konferenz mehrten sich dann die Stimmen, die ihr ein schlechtes Zeugnis ausstellten. Die dort erreichten Ergebnisse wurden als weitestgehend unzureichend bezeichnet und der Stellenwert der Rio-Konferenz relativiert: nicht mehr größter Gipfel aller Zeiten, sondern Einstieg in den glo-balen Dialog, den sogenannten Rio-Prozess. Dies kommt auch in einigen der Tagungsberichte von der VÖW-Tagung " Umwelt und Entwicklung ", die in diesem INFORMATIONSDIENST abgedruckt sind, zum Ausdruck. Udo Ernst Simonis, Professor für Umweltpolitik am Wissenschaftszentrum Berlin, analysiert in seinem Artikel die • tatsächlichen Ergebnisse der Rio-Konferenz und kommt zu der Einschätzung, daß dort durchaus auch beachtenswerte Abschlüsse und nicht nur der Einstieg in einen Verständigungsprozeß gelungen sind

Industrieller Metabolismus

Die industrielle Wirtschaftsweise gefährdet das globale ökologische System in doppelter Weise: Die anthropogen verursachten Stoffflüsse liegen durchwegs weit über den natürlichen, und die indu-striell bedingten Schadstoffemissionen übersteigen die Absorptionskapazität der natürlichen Senken. Das Konzept des " industriellen Metabolismus " eröffnet eine neue Perspektive für das Ver-stehen dieser Prozesse und den Umgang mit ihnen

Self-Organized Critical Noise Amplification in Human Closed Loop Control

When humans perform closed loop control tasks like in upright standing or while balancing a stick, their behavior exhibits non-Gaussian fluctuations with long-tailed distributions. The origin of these fluctuations is not known. Here, we investigate if they are caused by self-organized critical noise amplification which emerges in control systems when an unstable dynamics becomes stabilized by an adaptive controller that has finite memory. Starting from this theory, we formulate a realistic model of adaptive closed loop control by including constraints on memory and delays. To test this model, we performed psychophysical experiments where humans balanced an unstable target on a screen. It turned out that the model reproduces the long tails of the distributions together with other characteristic features of the human control dynamics. Fine-tuning the model to match the experimental dynamics identifies parameters characterizing a subject's control system which can be independently tested. Our results suggest that the nervous system involved in closed loop motor control nearly optimally estimates system parameters on-line from very short epochs of past observations

Eine Folge von Eem und 4 Weichsel-Interstadialen in Oerel/Niedersachsen und ihr Vegetationsablauf

An dem Interstadialvorkommen von Oerel im niedersächsischen Tiefland wurden umfangreiche geologische und vegetationsgeschichtliche Untersuchungen durchgeführt. Die Lokalität liegt in einer buchtförmigen Niederung am Osthang der Eisrandlage Lamstedter Staffel (Drenthe-2-Vorstoß der Saale-Kaltzeit). Sondierungen und Bohrungen ergaben ein ausgedehntes Eem-Vorkommen und darüber bis zu 4 durch Sande getrennte Weichsel-Interstadiale, die flächig ausgebildet sind. In der Umgebung des pollenanalytisch bearbeiteten Standardprofils OE 61 verlief die Entwicklung wie folgt: An der Basis liegen wahrscheinlich elster- sowie saalezeitliche Bildungen. Das Eem beginnt mit Abschnitt IV und ist bis VI limnisch, anschließend bis E VII sowie teilweise im Abschnitt WF I des Weichselfrüh-glazials als Torf ausgebildet. In den verschiedenen Stadialen wurde überwiegend reiner Sand abgelagert, dem Brörup -und Odderade-Interstadial gehen jedoch noch längere limnische Phasen voraus. Beide Interstadiale sind ebenso wie die jüngeren Interstadiale Oerel und Glinde als Torf ausgebildet. Die organogene Schichtenfolge im Bereich von OE 61 wird wie folgt eingeordnet bzw. neu benannt: Glinde-Interstadial, Oerel-Interstadial, Odderade-Interstadial, Brörup-Interstadial, Eem-Interglazial. Nach den pollenanalytischen Untersuchungen ist das Eem normal ausgebildet; Brörup und Odderade stellen zwei große bewaldete Interstadiale dar. Oerel und Glinde waren waldfrei mit Strauchtundra und gehören dem frühen Weichsel-Pleniglazial an, liegen also vor den niederländischen pleniglazialen Interstadialen. Vielleicht reicht das Glinde noch in den Beginn des Moershoofd-Komplexes.researc

Causally Investigating Cortical Dynamics and Signal Processing by Targeting Natural System Attractors With Precisely Timed (Electrical) Stimulation

Electrical stimulation is a promising tool for interacting with neuronal dynamics to identify neural mechanisms that underlie cognitive function. Since effects of a single short stimulation pulse typically vary greatly and depend on the current network state, many experimental paradigms have rather resorted to continuous or periodic stimulation in order to establish and maintain a desired effect. However, such an approach explicitly leads to forced and “unnatural” brain activity. Further, continuous stimulation can make it hard to parse the recorded activity and separate neural signal from stimulation artifacts. In this study we propose an alternate strategy: by monitoring a system in realtime, we use the existing preferred states or attractors of the network and apply short and precise pulses in order to switch between those states. When pushed into one of its attractors, one can use the natural tendency of the system to remain in such a state to prolong the effect of a stimulation pulse, opening a larger window of opportunity to observe the consequences on cognitive processing. To elaborate on this idea, we consider flexible information routing in the visual cortex as a prototypical example. When processing a stimulus, neural populations in the visual cortex have been found to engage in synchronized gamma activity. In this context, selective signal routing is achieved by changing the relative phase between oscillatory activity in sending and receiving populations (communication through coherence, CTC). In order to explore how perturbations interact with CTC, we investigate a network of interneuronal gamma (ING) oscillators composed of integrate-and-fire neurons exhibiting similar synchronization and signal routing phenomena. We develop a closed-loop stimulation paradigm based on the phase-response characteristics of the network and demonstrate its ability to establish desired synchronization states. By measuring information content throughout the model, we evaluate the effect of signal contamination caused by the stimulation in relation to the magnitude of the injected pulses and intrinsic noise in the system. Finally, we demonstrate that, up to a critical noise level, precisely timed perturbations can be used to artificially induce the effect of attention by selectively routing visual signals to higher cortical areas

Standardized Integrally Geared Turbomachines - Tailor Made For The Process Industry.

LecturePg. 131-144For more than 40 years, integrally geared centrifugal compressors have been in use worldwide, in the plant air sector first, and increasingly in the process industry. Apart from reliability, efficiency and operating range, the most striking features of this compressor concept, particular when used in the process industry, are the versatility and configurability of the machine. Today, all sorts of process gases, including toxic and flammable ones, can be compressed or expanded using integrally geared centrifugal compressor and expander units. The high level of modular construction employed in integrally geared turbomachines (IGTMs) allows for a high degree of standardization; the resulting building block system makes it possible to adapt the machine concept to each field of application and, in particular, to the customer's own requirements. Of prime importance here are the definition and geometry of the interfaces between the individual modules and equipment units, such as compressor and expansion stages, gear case, pinion shafts, seal systems, etc. The integrally geared centrifugal compressor has conquered many ranges of application in the process industry starting with compressors operated purely on air, followed by nitrogen and then carbon monoxide, carbon dioxide, chlorine, hydrocarbons, acetylenexide, and isobutyric aldehyde, and so forth. A recent success involving the compressing of high purity oxygen to high discharge pressures using integrally geared centrifugal compressors deserves special mention. It had been thought that this could only be achieved using single shaft compressors. This means that for oxygen, too, the advantages of integrally geared centrifugal compressors such as efficiency and very broad operating ranges can be used, as in the case of variable oxygen supply systems (varox) in air separation plants. Energy recovery in the process industry has presented integrally geared centrifugal compressors with a new task. Tail gases often have high energy contents which can be returned directly to a compression process in the same machine through addition of expander stages. In its original concept, the integrally geared centrifugal compressor is primarily suitable for the use of low-speed drive units. By using "free" pinion shaft extensions or additional pinion shafts, high speed drive units without an external intermediate gear can also be used. This aspect, together with the integration of expander stages already mentioned, leads to a very interesting and economical application of integrally geared centrifugal compressors: alongside compression and expansion functions, IGTMs can be used for mechanical output power distribution in sophisticated process equipment such as dimethylterephthalate (DMT) and pure terephthalic acid (PTA systems)

Visual backward masking: Modeling spatial and temporal aspects

In modeling visual backward masking, the focus has been on temporal effects. More specifically, an explanation has been sought as to why strongest masking can occur when the mask is delayed with respect to the target. Although interesting effects of the spatial layout of the mask have been found, only a few attempts have been made to model these phenomena. Here, we elaborate a structurally simple model which employs lateral excitation and inhibition together with different neural time scales to explain many spatial and temporal aspects of backward masking. We argue that for better understanding of visual masking, it is vitally important to consider the interplay of spatial and temporal factors together in one single model