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The present thesis deals with the mental representation of numbers in space. Generally it is assumed that numbers are mentally represented on a mental number line along which they ordered in a continuous and analogical manner. Dehaene, Bossini and Giraux (1993) found that the mental number line is spatially oriented from left-to-right. Using a parity-judgment task they observed faster left-hand responses for smaller numbers and faster right-hand responses for larger numbers. This effect has been labelled as Spatial Numerical Association of Response Codes (SNARC) effect. The first study of the present thesis deals with the question whether the spatial orientation of the mental number line derives from the writing system participants are adapted to. According to a strong ontogenetic interpretation the SNARC effect should only obtain for effectors closely related to the comprehension and production of written language (hands and eyes). We asked participants to indicate the parity status of digits by pressing a pedal with their left or right foot. In contrast to the strong ontogenetic view we observed a pedal SNARC effect which did not differ from the manual SNARC effect. In the second study we evaluated whether the SNARC effect reflects an association of numbers and extracorporal space or an association of numbers and hands. To do so we varied the spatial arrangement of the response buttons (vertical vs. horizontal) and the instruction (handrelated vs. button-related). For vertically arranged buttons and a buttonrelated instruction we found a button-related SNARC effect. In contrast, for a hand-related instruction we obtained a hand-related SNARC effect. For horizontally arranged buttons and a handrelated instruction, however, we found a buttonrelated SNARC effect. The results of the first to studies were interpreted in terms of weak ontogenetic view. In the third study we aimed to examine the functional locus of the SNARC effect. We used the psychological refractory period paradigm. In the first experiment participants first indicated the pitch of a tone and then the parity status of a digit (locus-of-slack paradigma). In a second experiment the order of stimulus presentation and thus tasks changed (effect-propagation paradigm). The results led us conclude that the SNARC effect arises while the response is centrally selected. In our fourth study we test for an association of numbers and time. We asked participants to compare two serially presented digits. Participants were faster to compare ascending digit pairs (e.g., 2-3) than descending pairs (e.g., 3-2). The pattern of our results was interpreted in terms of forwardassociations (“1-2-3”) as formed by our ubiquitous cognitive routines to count of objects or events.
I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae. I supplement my {3+1} GR hydrodynamic simulations with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on (1) the late postbounce gravitational wave emission owing to convective overturn, anisotropic neutrino emission and protoneutron star pulsations, and (2) on the gravitational wave signature of accretion-induced collapse of white dwarfs to neutron stars.
The properties of a series of well-defined new surfactant oligomers (dimers to tetramers)were examined. From a molecular point of view, these oligomeric surfactants consist of simple monomeric cationic surfactant fragments coupled via the hydrophilic ammonium chloride head groups by spacer groups (different in nature and length). Properties of these cationic surfactant oligomers in aqueous solution such as solubility, micellization and surface activity, micellar size and aggregation number were discussed with respect to the two new molecular variables introduced, i.e. degree of oligomerization and spacer group, in order to establish structure – property relationships. Thus, increasing the degree of oligomerization results in a pronounced decrease of the critical micellization concentration (CMC). Both reduced spacer length and increased spacer hydrophobicity lead to a decrease of the CMC, but to a lesser extent. For these particular compounds, the formed micelles are relatively small and their aggregation number decreases with increasing the degree of oligomerization, increasing spacer length and sterical hindrance. In addition, pseudo-phase diagrams were established for the dimeric surfactants in more complex systems, namely inverse microemulsions, demonstrating again the important influence of the spacer group on the surfactant behaviour. Furthermore, the influence of additives on the property profile of the dimeric compounds was examined, in order to see if the solution properties can be improved while using less material. Strong synergistic effects were observed by adding special organic salts (e.g. sodium salicylate, sodium vinyl benzoate, etc.) to the surfactant dimers in stoichiometric amounts. For such mixtures, the critical aggregation concentration is strongly shifted to lower concentration, the effect being more pronounced for dimers than for analogous monomers. A sharp decrease of the surface tension can also be attained. Many of the organic anions produce viscoelastic solutions when added to the relatively short-chain dimers in aqueous solution, as evidenced by rheological measurements. This behaviour reflects the formation of entangled wormlike micelles due to strong interactions of the anions with the cationic surfactants, decreasing the curvature of the micellar aggregates. It is found that the associative behaviour is enhanced by dimerization. For a given counterion, the spacer group may also induce a stronger viscosifying effect depending on its length and hydrophobicity. Oppositely charged surfactants were combined with the cationic dimers, too. First, some mixtures with the conventional anionic surfactant SDS revealed vesicular aggregates in solution. Also, in view of these catanionic mixtures, a novel anionic dimeric surfactant based on EDTA was synthesized and studied. The synthesis route is relatively simple and the compound exhibits particularly appealing properties such as low CMC and σCMC values, good solubilization capacity of hydrophobic probes and high tolerance to hard water. Noteworthy, mixtures with particular cationic dimers gave rise to viscous solutions, reflecting the micelle growth.
Die Arbeit untersucht die Annahme einer unterschiedlichen Gewichtung von distinktiven enzyklopädischen, funktionalen und sensorischen Merkmalen innerhalb der Repräsentationen von Objekten der belebten und unbelebten semantischen Domäne. Hierzu wurde ein Reaktionszeitexperiment zur Merkmalsverifikation durchgeführt. Vorab wurden deutsche Normen über das geschätzte Erwerbsalter für 244 Stimuli aus dem Korpus von Snodgrass & Vanderwart (1980) erhoben. Weiterhin wurde eine Datenbank von Merkmalsnormen für 80 konkrete Objektbegriffe erstellt. Insgesamt wurden zwei Reaktionszeitexperimente durchgeführt, die sich lediglich durch die Darbietungsdauer des Konzeptbegriffes unterschieden. Der Konzeptbegriff wurde entweder 1000 ms (lange Darbietung) oder 250 ms (kurze Darbietung) präsentiert, bevor das zu verifizierende semantische Merkmal erschien. Bei langer Präsentationszeit des Objektbegriffes zeigten sich für Objekte der unbelebten Domäne schnellere Reaktionszeiten beim Verifizieren von distinktiven funktionalen Merkmalen als beim Verifizieren von distinktiven enzyklopädischen Merkmalen. Dieser Effekt wurde bei kurzer Darbietungsdauer des Konzeptbegriffes repliziert. Bei kurzer Darbietung konnten für Objekte der unbelebten Domäne zusätzlich kürzere Reaktionszeiten beim Verifizieren distinktiver funktionaler Merkmale als beim Verifizieren distinktiver sensorischer Merkmale beobachtet werden. Für Objekte der belebten Domäne lagen weder nach kurzer noch nach langer Präsentation des Objektbegriffes Unterschiede in den Reaktionszeiten beim Verifizieren der semantischen Merkmale vor. Die Ergebnisse werden vor dem Hintergrund aktueller neurolinguistischer Modelle zur Organisation des semantischen Gedächtnisses diskutiert. Die Ergebnisse deuten darauf hin, dass innerhalb der Objektrepräsentationen belebter Objekte alle drei Merkmalstypen interkorrelieren. Für Objekte der unbelebten Domäne werden starke Interkorrelationen zwischen funktionalen und sensorischen Merkmalen angenommen. Zusätzlich wird davon ausgegangen, dass distinktive funktionale Merkmale innerhalb der Repräsentationen unbelebter Objekte besonders stark gewichtet sind.
Die kumulative Dissertation umfasst dreizehn Beiträge, die zwischen 1994 und 2006 aus je aktuellen Forschungszusammenhängen entstanden sind und in unterschiedlichen Zeitschriften und Sammelwerken publiziert wurden. Sie widmen sich Funktion und Leistung der Bibliothek für Bildungsgeschichtliche Forschung (BBF) als bildungshistorischer Forschungsbibliothek, die in einer Einleitung entlang einer professionstheoretischen Fragestellung systematisch eingeordnet werden. Beiträge und Einleitung gehen zum einen auf die Bestandsgeschichte der Vorgängereinrichtungen der BBF ein, die als Gebrauchsbibliotheken insbesondere eine institutionelle Grundlage zur Verberuflichung und Professionalisierung der Lehrer bildeten. Zum anderen widmen sie sich neueren Angeboten der 1992 in eine Forschungsbibliothek umgewandelten Einrichtung, die sich besonders an dem Bedarf des veränderten Adressatenkreises orientieren. Es handelt sich um Dienstleistungen, die einerseits dem Kontext einer digitalen Bibliothek zuzuordnen sind, andererseits das Konzept einer Forschungsbibliothek zu einer Forschungsstätte erweitern, mit der Aufgabe, zur Unterstützung des interdisziplinären und internationalen Diskurses der an Themen zur historischen Bildungsforschung arbeitenden Science Community beizutragen.
Förster Resonance Energy Transfer (FRET) plays an important role for biochemical applications such as DNA sequencing, intracellular protein-protein interactions, molecular binding studies, in vitro diagnostics and many others. For qualitative and quantitative analysis, FRET systems are usually assembled through molecular recognition of biomolecules conjugated with donor and acceptor luminophores. Lanthanide (Ln) complexes, as well as semiconductor quantum dot nanocrystals (QD), possess unique photophysical properties that make them especially suitable for applied FRET. In this work the possibility of using QD as very efficient FRET acceptors in combination with Ln complexes as donors in biochemical systems is demonstrated. The necessary theoretical and practical background of FRET, Ln complexes, QD and the applied biochemical models is outlined. In addition, scientific as well as commercial applications are presented. FRET can be used to measure structural changes or dynamics at distances ranging from approximately 1 to 10 nm. The very strong and well characterized binding process between streptavidin (Strep) and biotin (Biot) is used as a biomolecular model system. A FRET system is established by Strep conjugation with the Ln complexes and QD biotinylation. Three Ln complexes (one with Tb3+ and two with Eu3+ as central ion) are used as FRET donors. Besides the QD two further acceptors, the luminescent crosslinked protein allophycocyanin (APC) and a commercial fluorescence dye (DY633), are investigated for direct comparison. FRET is demonstrated for all donor-acceptor pairs by acceptor emission sensitization and a more than 1000-fold increase of the luminescence decay time in the case of QD reaching the hundred microsecond regime. Detailed photophysical characterization of donors and acceptors permits analysis of the bioconjugates and calculation of the FRET parameters. Extremely large Förster radii of more than 100 Å are achieved for QD as acceptors, considerably larger than for APC and DY633 (ca. 80 and 60 Å). Special attention is paid to interactions with different additives in aqueous solutions, namely borate buffer, bovine serum albumin (BSA), sodium azide and potassium fluoride (KF). A more than 10-fold limit of detection (LOD) decrease compared to the extensively characterized and frequently used donor-acceptor pair of Europium tris(bipyridine) (Eu-TBP) and APC is demonstrated for the FRET system, consisting of the Tb complex and QD. A sub-picomolar LOD for QD is achieved with this system in azide free borate buffer (pH 8.3) containing 2 % BSA and 0.5 M KF. In order to transfer the Strep-Biot model system to a real-life in vitro diagnostic application, two kinds of imunnoassays are investigated using human chorionic gonadotropin (HCG) as analyte. HCG itself, as well as two monoclonal anti-HCG mouse-IgG (immunoglobulin G) antibodies are labeled with the Tb complex and QD, respectively. Although no sufficient evidence for FRET can be found for a sandwich assay, FRET becomes obvious in a direct HCG-IgG assay showing the feasibility of using the Ln-QD donor-acceptor pair as highly sensitive analytical tool for in vitro diagnostics.
The separation of natural and anthropogenically caused climatic changes is an important task of contemporary climate research. For this purpose, a detailed knowledge of the natural variability of the climate during warm stages is a necessary prerequisite. Beside model simulations and historical documents, this knowledge is mostly derived from analyses of so-called climatic proxy data like tree rings or sediment as well as ice cores. In order to be able to appropriately interpret such sources of palaeoclimatic information, suitable approaches of statistical modelling as well as methods of time series analysis are necessary, which are applicable to short, noisy, and non-stationary uni- and multivariate data sets. Correlations between different climatic proxy data within one or more climatological archives contain significant information about the climatic change on longer time scales. Based on an appropriate statistical decomposition of such multivariate time series, one may estimate dimensions in terms of the number of significant, linear independent components of the considered data set. In the presented work, a corresponding approach is introduced, critically discussed, and extended with respect to the analysis of palaeoclimatic time series. Temporal variations of the resulting measures allow to derive information about climatic changes. For an example of trace element abundances and grain-size distributions obtained near the Cape Roberts (Eastern Antarctica), it is shown that the variability of the dimensions of the investigated data sets clearly correlates with the Oligocene/Miocene transition about 24 million years before present as well as regional deglaciation events. Grain-size distributions in sediments give information about the predominance of different transportation as well as deposition mechanisms. Finite mixture models may be used to approximate the corresponding distribution functions appropriately. In order to give a complete description of the statistical uncertainty of the parameter estimates in such models, the concept of asymptotic uncertainty distributions is introduced. The relationship with the mutual component overlap as well as with the information missing due to grouping and truncation of the measured data is discussed for a particular geological example. An analysis of a sequence of grain-size distributions obtained in Lake Baikal reveals that there are certain problems accompanying the application of finite mixture models, which cause an extended climatological interpretation of the results to fail. As an appropriate alternative, a linear principal component analysis is used to decompose the data set into suitable fractions whose temporal variability correlates well with the variations of the average solar insolation on millenial to multi-millenial time scales. The abundance of coarse-grained material is obviously related to the annual snow cover, whereas a significant fraction of fine-grained sediments is likely transported from the Taklamakan desert via dust storms in the spring season.
The terrestrial biosphere impacts considerably on the global carbon cycle. In particular, ecosystems contribute to set off anthropogenic induced fossil fuel emissions and hence decelerate the rise of the atmospheric CO₂ concentration. However, the future net sink strength of an ecosystem will heavily depend on the response of the individual processes to a changing climate. Understanding the makeup of these processes and their interaction with the environment is, therefore, of major importance to develop long-term climate mitigation strategies. Mathematical models are used to predict the fate of carbon in the soil-plant-atmosphere system under changing environmental conditions. However, the underlying processes giving rise to the net carbon balance of an ecosystem are complex and not entirely understood at the canopy level. Therefore, carbon exchange models are characterised by considerable uncertainty rendering the model-based prediction into the future prone to error. Observations of the carbon exchange at the canopy scale can help learning about the dominant processes and hence contribute to reduce the uncertainty associated with model-based predictions. For this reason, a global network of measurement sites has been established that provides long-term observations of the CO₂ exchange between a canopy and the atmosphere along with micrometeorological conditions. These time series, however, suffer from observation uncertainty that, if not characterised, limits their use in ecosystem studies. The general objective of this work is to develop a modelling methodology that synthesises physical process understanding with the information content in canopy scale data as an attempt to overcome the limitations in both carbon exchange models and observations. Similar hybrid modelling approaches have been successfully applied for signal extraction out of noisy time series in environmental engineering. Here, simple process descriptions are used to identify relationships between the carbon exchange and environmental drivers from noisy data. The functional form of these relationships are not prescribed a priori but rather determined directly from the data, ensuring the model complexity to be commensurate with the observations. Therefore, this data-led analysis results in the identification of the processes dominating carbon exchange at the ecosystem scale as reflected in the data. The description of these processes may then lead to robust carbon exchange models that contribute to a faithful prediction of the ecosystem carbon balance. This work presents a number of studies that make use of the developed data-led modelling approach for the analysis and interpretation of net canopy CO₂ flux observations. Given the limited knowledge about the underlying real system, the evaluation of the derived models with synthetic canopy exchange data is introduced as a standard procedure prior to any real data employment. The derived data-led models prove successful in several different applications. First, the data-based nature of the presented methods makes them particularly useful for replacing missing data in the observed time series. The resulting interpolated CO₂ flux observation series can then be analysed with dynamic modelling techniques, or integrated to coarser temporal resolution series for further use e.g., in model evaluation exercises. However, the noise component in these observations interferes with deterministic flux integration in particular when long time periods are considered. Therefore, a method to characterise the uncertainties in the flux observations that uses a semi-parametric stochastic model is introduced in a second study. As a result, an (uncertain) estimate of the annual net carbon exchange of the observed ecosystem can be inferred directly from a statistically consistent integration of the noisy data. For the forest measurement sites analysed, the relative uncertainty for the annual sum did not exceed 11 percent highlighting the value of the data. Based on the same models, a disaggregation of the net CO₂ flux into carbon assimilation and respiration is presented in a third study that allows for the estimation of annual ecosystem carbon uptake and release. These two components can then be further analysed for their separate response to environmental conditions. Finally, a fourth study demonstrates how the results from data-led analyses can be turned into a simple parametric model that is able to predict the carbon exchange of forest ecosystems. Given the global network of measurements available the derived model can now be tested for generality and transferability to other biomes. In summary, this work particularly highlights the potential of the presented data-led methodologies to identify and describe dominant carbon exchange processes at the canopy level contributing to a better understanding of ecosystem functioning.
Polyelectrolyte microcapsules containing stimuli-responsive polymers have potential applications in the fields of sensors or actuators, stimulable microcontainers and controlled drug delivery. Such capsules were prepared, with the focus on pH-sensitivity and carbohydrate-sensing. First, pH-responsive polyelectrolyte capsules were produced by means of electrostatic layer-by-layer assembly of oppositely charged weak polyelectrolytes onto colloidal templates that were subsequently removed. The capsules were composed of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) or poly(4-vinylpyridine) (P4VP) and PMA and varied considerably in their hydrophobicity and the influence of secondary interactions. These polymers were assembled onto CaCO3 and SiO2 particles with diameters of ~ 5 µm, and a new method for the removal of the silica template under mild conditions was proposed. The pH-dependent stability of PAH/PMA and P4VP/PMA capsules was studied by confocal laser scanning microscopy (CLSM). They were stable over a wide pH-range and exhibited a pronounced swelling at the edges of stability, which was attributed to uncompensated positive or negative charges within the multilayers. The swollen state could be stabilized when the electrostatic repulsion was counteracted by hydrogen-bonding, hydrophobic interactions or polymeric entanglement. This stabilization made it possible to reversibly swell and shrink the capsules by tuning the pH of the solution. The pH-dependent ionization degree of PMA was used to modulate the binding of calcium ions. In addition to the pH-sensitivity, the stability and the swelling degree of these capsules at a given pH could be modified, when the ionic strength of the medium was altered. The reversible swelling was accompanied by reversible permeability changes for low and high molecular weight substances. The permeability for glucose was evaluated by studying the time-dependence of the buckling of the capsule walls in glucose solutions and the reversible permeability modulation was used for the encapsulation of polymeric material. A theoretical model was proposed to explain the pH-dependent size variations that took into account an osmotic expanding force and an elastic restoring force to evaluate the pH-dependent size changes of weak polyelectrolyte capsules. Second, sugar-sensitive multilayers were assembled using the reversible covalent ester formation between the polysaccharide mannan and phenylboronic acid moieties that were grafted onto poly(acrylic acid) (PAA). The resulting multilayer films were sensitive to several carbohydrates, showing the highest sensitivity to fructose. The response to carbohydrates resulted from the competitive binding of small molecular weight sugars and mannan to the boronic acid groups within the film, and was observed as a fast dissolution of the multilayers, when they were brought into contact with the sugar-containing solution above a critical concentration. It was also possible to prepare carbohydrate-sensitive multilayer capsules, and their sugar-dependent stability was investigated by following the release of encapsulated rhodamine-labeled bovine serum albumin (TRITC-BSA).
Semantische Repräsentation, obligatorische Aktivierung und verbale Produktion arithmetischer Fakten
(2006)
Die vorliegende Arbeit widmet sich der Repräsentation und Verarbeitung arithmetischer Fakten. Dieser Bereich semantischen Wissens eignet sich unter anderem deshalb besonders gut als Forschungsgegenstand, weil nicht nur seine einzelne Bestandteile, sondern auch die Beziehungen dieser Bestandteile untereinander außergewöhnlich gut definierbar sind. Kognitive Modelle können also mit einem Grad an Präzision entwickelt werden, der in anderen Bereichen kaum je zu erreichen sein wird. Die meisten aktuellen Modelle stimmen darin überein, die Repräsentation arithmetischer Fakten als eine assoziative, netzwerkartig organisierte Struktur im deklarativen Gedächtnis zu beschreiben. Trotz dieser grundsätzlichen Übereinstimmung bleibt eine Reihe von Fragen offen. In den hier vorgestellten Untersuchungen werden solche offene Fragen in Hinsicht auf drei verschiedene Themenbereiche angegangen: 1) die neuroanatomischen Korrelate 2) Nachbarschaftskonsistenzeffekte bei der verbalen Produktion sowie 3) die automatische Aktivierung arithmetischer Fakten. In einer kombinierten fMRT- und Verhaltensstudie wurde beispielsweise der Frage nachgegangen, welche neurofunktionalen Entsprechungen es für den Erwerb arithmetischer Fakten bei Erwachsenen gibt. Den Ausgangspunkt für diese Untersuchung bildete das Triple-Code-Modell von Dehaene und Cohen, da es als einziges auch Aussagen über neuroanatomische Korrelate numerischer Leistungen macht. Das Triple-Code-Modell geht davon aus, dass zum Abruf arithmetischer Fakten eine „perisylvische“ Region der linken Hemisphäre unter Einbeziehung der Stammganglien sowie des Gyrus angularis nötig ist (Dehaene & Cohen, 1995; Dehaene & Cohen, 1997; Dehaene, Piazza, Pinel, & Cohen, 2003). In der aktuellen Studie sollten gesunde Erwachsene komplexe Multiplikationsaufgaben etwa eine Woche lang intensiv üben, so dass ihre Beantwortung immer mehr automatisiert erfolgt. Die Lösung dieser geübten Aufgaben sollte somit – im Gegensatz zu vergleichbaren ungeübten Aufgaben – immer stärker auf Faktenabruf als auf der Anwendung von Prozeduren und Strategien beruhen. Hingegen sollten ungeübte Aufgaben im Vergleich zu geübten höhere Anforderungen an exekutive Funktionen einschließlich des Arbeitsgedächtnisses stellen. Nach dem Training konnten die Teilnehmer – wie erwartet – geübte Aufgaben deutlich schneller und sicherer beantworten als ungeübte. Zusätzlich wurden sie auch im Magnetresonanztomografen untersucht. Dabei konnte zunächst bestätigt werden, dass das Lösen von Multiplikationsaufgaben allgemein von einem vorwiegend linkshemisphärischen Netzwerk frontaler und parietaler Areale unterstützt wird. Das wohl wichtigste Ergebnis ist jedoch eine Verschiebung der Hirnaktivierungen von eher frontalen Aktivierungsmustern zu einer eher parietalen Aktivierung und innerhalb des Parietallappens vom Sulcus intraparietalis zum Gyrus angularis bei den geübten im Vergleich zu den ungeübten Aufgaben. So wurde die zentrale Bedeutung von Arbeitsgedächtnis- und Planungsleistungen für komplexe ungeübte Rechenaufgaben erneut herausgestellt. Im Sinne des Triple-Code-Modells könnte die Verschiebung innerhalb des Parietallappens auf einen Wechsel von quantitätsbasierten Rechenleistungen (Sulcus intraparietalis) zu automatisiertem Faktenabruf (linker Gyrus angularis) hindeuten. Gibt es bei der verbalen Produktion arithmetischer Fakten Nachbarschaftskonsistenzeffekte ähnlich zu denen, wie sie auch in der Sprachverarbeitung beschrieben werden? Solche Effekte sind nach dem aktuellen „Dreiecksmodell“ von Verguts & Fias (2004) zur Repräsentation von Multiplikationsfakten erwartbar. Demzufolge sollten richtige Antworten leichter gegeben werden können, wenn sie Ziffern mit möglichst vielen semantisch nahen falschen Antworten gemeinsam haben. Möglicherweise sollten demnach aber auch falsche Antworten dann mit größerer Wahrscheinlichkeit produziert werden, wenn sie eine Ziffer mit der richtigen Antwort teilen. Nach dem Dreiecksmodell wäre darüber hinaus sogar der klassische Aufgabengrößeneffekt bei einfachen Multiplikationsaufgaben (Zbrodoff & Logan, 2004) auf die Konsistenzverhältnisse der richtigen Antwort mit semantisch benachbarten falschen Antworten zurückzuführen. In einer Reanalyse der Fehlerdaten von gesunden Probanden (Campbell, 1997) und einem Patienten (Domahs, Bartha, & Delazer, 2003) wurden tatsächlich Belege für das Vorhandensein von Zehnerkonsistenzeffekten beim Lösen einfacher Multiplikationsaufgaben gefunden. Die Versuchspersonen bzw. der Patient hatten solche falschen Antworten signifikant häufiger produziert, welche die gleiche Zehnerziffer wie das richtigen Ergebnisses aufwiesen, als ansonsten vergleichbare andere Fehler. Damit wird die Annahme unterstützt, dass die Zehner- und die Einerziffern zweistelliger Zahlen separate Repräsentationen aufweisen – bei der Multiplikation (Verguts & Fias, 2004) wie auch allgemein bei numerischer Verarbeitung (Nuerk, Weger, & Willmes, 2001; Nuerk & Willmes, 2005). Zusätzlich dazu wurde in einer Regressionsanalyse über die Fehlerzahlen auch erstmalig empirische Evidenz für die Hypothese vorgelegt, dass der klassische Aufgabengrößeneffekt beim Abruf von Multiplikationsfakten auf Zehnerkonsistenzeffekte zurückführbar ist: Obwohl die Aufgabengröße als erster Prädiktor in das Modell einging, wurde diese Variable wieder verworfen, sobald ein Maß für die Nachbarschaftskonsistenz der richtigen Antwort in das Modell aufgenommen wurde. Schließlich wurde in einer weiteren Studie die automatische Aktivierung von Multiplikationsfakten bei gesunden Probanden mit einer Zahlenidentifikationsaufgabe (Galfano, Rusconi, & Umilta, 2003; Lefevre, Bisanz, & Mrkonjic, 1988; Thibodeau, Lefevre, & Bisanz, 1996) untersucht. Dabei sollte erstmals die Frage beantwortet werden, wie sich die automatische Aktivierung der eigentlichen Multiplikationsergebnisse (Thibodeau et al., 1996) zur Aktivierung benachbarter falscher Antworten (Galfano et al., 2003) verhält. Ferner sollte durch die Präsentation mit verschiedenen SOAs der zeitliche Verlauf dieser Aktivierungen aufgeklärt werden. Die Ergebnisse dieser Studie können insgesamt als Evidenz für das Vorhandensein und die automatische, obligatorische Aktivierung eines Netzwerkes arithmetischer Fakten bei gesunden, gebildeten Erwachsenen gewertet werden, in dem die richtigen Produkte stärker mit den Faktoren assoziiert sind als benachbarte Produkte (Operandenfehler). Dabei führen Produkte kleiner Aufgaben zu einer stärkeren Interferenz als Produkte großer Aufgaben und Operandenfehler großer Aufgaben zu einer stärkeren Interferenz als Operandenfehler kleiner Aufgaben. Ein solches Aktivierungsmuster passt gut zu den Vorhersagen des Assoziationsverteilungsmodells von Siegler (Lemaire & Siegler, 1995; Siegler, 1988), bei dem kleine Aufgaben eine schmalgipflige Verteilung der Assoziationen um das richtige Ergebnis herum aufweisen, große Aufgaben jedoch eine breitgipflige Verteilung. Somit sollte die vorliegende Arbeit etwas mehr Licht in bislang weitgehend vernachlässigte Aspekte der Repräsentation und des Abrufs arithmetischer Fakten gebracht haben: Die neuronalen Korrelate ihres Erwerbs, die Konsequenzen ihrer Einbindung in das Stellenwertsystem mit der Basis 10 sowie die spezifischen Auswirkungen ihrer assoziativen semantischen Repräsentation auf ihre automatische Aktivierbarkeit. Literatur Campbell, J. I. (1997). 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