Birkbeck College London

London, United Kingdom

Birkbeck College London

London, United Kingdom
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Kiss M.,Birkbeck College London | Grubert A.,Birkbeck College London | Grubert A.,University of Fribourg | Petersen A.,Copenhagen University | Eimer M.,Birkbeck College London
Journal of Cognitive Neuroscience | Year: 2012

The question whether attentional capture by salient but task-irrelevant visual stimuli is triggered in a bottom-up fashion or depends on top-down task settings is still unresolved. Strong support for bottom-up capture was obtained in the additional singleton task, in which search arrays were visible until response onset. Equally strong evidence for top-down control of attentional capture was obtained in spatial cueing experiments in which display durations were very brief. To demonstrate the critical role of temporal task demands on salience-driven attentional capture, we measured ERP indicators of capture by task-irrelevant color singletons in search arrays that could also contain a shape target. In Experiment 1, all displays were visible until response onset. In Experiment 2, display duration was limited to 200 msec. With long display durations, color singleton distractors elicited an N2pc component that was followed by a late Pd component, suggesting that they triggered attentional capture, which was later replaced by location-specific inhibition. When search arrays were visible for only 200 msec, the distractor-elicited N2pc was eliminated and was replaced by a Pd component in the same time range, indicative of rapid suppression of capture. Results show that attentional capture by salient distractors can be inhibited for short-duration search displays, in which it would interfere with target processing. They demonstrate that salience-driven capture is not a purely bottom-up phenomenon but is subject to top-down control. © 2012 Massachusetts Institute of Technology.


Green D.W.,University College London | Wei L.,Birkbeck College London
Language, Cognition and Neuroscience | Year: 2014

Code-switching (CS) is central to many bilingual communities and, though linguistic and sociolinguistic research has characterised different types of code-switches (alternations, insertions, dense CS), the cognitive control processes (CPs) that mediate them are not well understood. A key issue is how during CS speakers produce the right words in the right order. In speech, serial order emerges from a speech plan in which items are represented in parallel. We propose that entry into the mechanism for speech planning (a competitive queuing mechanism) is governed by CPs best suited to the particular types of code-switches. Language task schemas external to the language network govern access. In CS, they are coordinated cooperatively and operate in a coupled or in an open control mode. The former permits alternations and insertions whereas the latter is required for dense CS. We explore predictions of this CP model and its implications for CS research. © 2014 Taylor & Francis.


Tollner T.,Ludwig Maximilians University of Munich | Zehetleitner M.,Ludwig Maximilians University of Munich | Krummenacher J.,University of Fribourg | Muller H.J.,Ludwig Maximilians University of Munich | Muller H.J.,Birkbeck College London
Journal of Cognitive Neuroscience | Year: 2011

The redundant-signals effect (RSE) refers to a speed-up of RT when the response is triggered by two, rather than just one, response-relevant target elements. Although there is agreement that in the visual modality RSEs observed with dimensionally redundant signals originating from the same location are generated by coactive processing architectures, there has been a debate as to the exact stage(s) - preattentive versus postselective - of processing at which coactivation arises. To determine the origin(s) of redundancy gains in visual pop-out search, the present study combined mental chronometry with electrophysiological markers that reflect purely preattentive perceptual (posterior-contralateral negativity [PCN]), preattentive and postselective perceptual plus response selection-related (stimulus-locked lateralized readiness potential [LRP]), or purely response production-related processes (response-locked LRP). As expected, there was an RSE on target detection RTs, with evidence for coactivation. At the electrophysiological level, this pattern was mirrored by an RSE in PCN latencies, whereas stimulus-locked LRP latencies showed no RSE over and above the PCN effect. Also, there was no RSE on the response-locked LRPs. This pattern demonstrates a major contribution of preattentive perceptual processing stages to the RSE in visual pop-out search, consistent with parallel-coactive coding of target signals in multiple visual dimensions [Müller, H. J., Heller, D., & Ziegler, J. Visual search for singleton feature targets within and across feature dimensions. © 2010 Massachusetts Institute of Technology.


Conci M.,Ludwig Maximilians University of Munich | Tollner T.,Ludwig Maximilians University of Munich | Leszczynski M.,Ludwig Maximilians University of Munich | Muller H.J.,Ludwig Maximilians University of Munich | Muller H.J.,Birkbeck College London
Neuropsychologia | Year: 2011

Object configurations can be perceptually represented at various hierarchical levels. For example, in visual search, global Kanizsa figures are detected efficiently, whereas search for local groupings is inefficient, with similarity-dependent nontarget interference arising at the hierarchical level that defines the target (Conci, Müller, & Elliott, 2007). The present study was designed to examine the electrophysiological correlates of this global-local search asymmetry. The results revealed differences between hierarchical object levels to be evident throughout a number of processing stages: search for a global, versus a local, target elicited larger amplitudes in early sensory components (P1, N1). Moreover, the efficiency of attentional orienting towards a target was mirrored in the Posterior Contralateral Negativity (PCN), with PCN latencies being substantially delayed (by ∼70. ms) with local, versus global, targets. Finally, late components (P3 and slow wave-SW) reflected the overall search efficiency, which was determined by both the hierarchical level at which the target was defined and the similarity-based nontarget interference. Taken together, this pattern shows that multiple, sequential processes of object completion contribute to the attentional precedence of a globally bound object over a mere local element grouping. © 2011 Elsevier Ltd.


Olivers C.N.L.,VU University Amsterdam | Eimer M.,Birkbeck College London
Neuropsychologia | Year: 2011

Previous work has shown that distractors present in a visual search display attract attention when they match objects kept in visual working memory. It seems that maintaining an object in working memory is functionally identical to adopting an attentional set for that object. We test this conjecture by asking observers to perform a memory task as well as a visual search task (in which memory-related distractors could return), but to leave the observer uncertain as to which of these tasks would have to be completed first. This way, observers ought to more readily look for the memorized information, rather than just remember it. Memory-related distractor effects were larger than when participants knew the order of the tasks beforehand, consistent with the idea that trying to attend to something involves additional processes or representations beyond those needed for simply storing an item. © 2010 Elsevier Ltd.


Pedersen R.B.,University of Bergen | Searle M.P.,University of Oxford | Carter A.,Birkbeck College London | Bandopadhyay P.C.,Geological Survey of India
Journal of the Geological Society | Year: 2010

The Andaman ophiolites form the basement of the Andaman Islands, which is a part of the outer forearc that links the Indo-Burma accretionary complex to the north with the Java-Sumatra trench-arc system to the SE. Upper mantle harzburgite and dunite are overlain by a cumulate peridotite-gabbro complex, highlevel intrusive rocks and a tholeiitic volcanic series. The upper crust in the South Andaman ophiolite shows also a prominent andesite-dacite volcanic suite, suggesting arc volcanism built onto ocean crust. U-Pb zircon dating of a trondhjemitic rock from Chiriya Tapu in South Andaman Island using laser ablation inductively coupled mass spectrometry reveals an age of crustal formation of 95 ± 2 Ma. The trondhjemites have geochemistry comparable with that of plagiogranites associated with ophiolite complexes, and Nd values around +7 further confirm that they are derived from depleted mantle melts. Basaltic pillow lava and basaltic dykes that cut the trondhjemites have mid-ocean ridge basalt-like trace-element geochemistry. The new data show that the Andaman volcanic arc was built on Cenomanian ophiolite-oceanic crust and that subduction was initiated at this time along Tethys, at least from Cyprus through Oman to the Andaman Islands. © 2010 Geological Society of London.


Kontchakov R.,Birkbeck College London | Wolter F.,University of Liverpool | Zakharyaschev M.,Birkbeck College London
Artificial Intelligence | Year: 2010

We develop a formal framework for comparing different versions of ontologies, and apply it to ontologies formulated in terms of DL-Lite, a family of 'lightweight' description logics designed for data-intensive applications. The main feature of our approach is that we take into account the vocabulary (=signature) with respect to which one wants to compare ontologies. Five variants of difference and inseparability relations between ontologies are introduced and their respective applications for ontology development and maintenance discussed. These variants are obtained by generalising the notion of conservative extension from mathematical logic and by distinguishing between differences that can be observed among concept inclusions, answers to queries over ABoxes, by taking into account additional context ontologies, and by considering a model-theoretic, language-independent notion of difference. We compare these variants, study their meta-properties, determine the computational complexity of the corresponding reasoning tasks, and present decision algorithms. Moreover, we show that checking inseparability can be automated by means of encoding into QBF satisfiability and using off-the-shelf general purpose QBF solvers. Inseparability relations between ontologies are then used to develop a formal framework for (minimal) module extraction. We demonstrate that different types of minimal modules induced by these inseparability relations can be automatically extracted from real-world medium-size DL-Lite ontologies by composing the known tractable syntactic locality-based module extraction algorithm with our non-tractable extraction algorithms and using the multi-engine QBF solver aqme. Finally, we explore the relationship between uniform interpolation (or forgetting) and inseparability. © 2010 Elsevier B.V. All rights reserved.


Crawford I.A.,Birkbeck College London
Astronomy and Geophysics | Year: 2012

Ian Crawford explains why human space exploration will tell us more about the solar system than robotic exploration alone. © 2012 Royal Astronomical Society.


Crawford I.A.,Birkbeck College London
JBIS - Journal of the British Interplanetary Society | Year: 2016

In this paper we outline the range of probes and scientific instruments that will be required for an Icarus-style interstellar mission to fulfill its scientific objectives of exploring a nearby star, its attendant planetary system, and the intervening interstellar medium. Based on this preliminary analysis, we estimate that the minimum total Icarus scientific payload mass will be in the region of 100 tonnes. Of this, approximately 10 tonnes would be allocated for cruise-phase science instruments (not all of which would necessarily need to be decelerated at the target system), and about 35 tonnes would be contributed by the intra-system science payload itself (i.e. the dry mass of the stellar and planetary probes and their instruments). The remaining ∼55 tonnes is allocated for the sub-probe intra-system propulsion requirements (crudely estimated from current Solar System missions; detailed modelling of sub-probe propulsion systems will be needed to refine this figure). However, the overall mass contributed by the science payload to the total that must be decelerated from the interstellar cruise velocity will be significantly more than 100 tonnes, as allowance must be made for the payload structural and infrastructural elements required to support, deploy, and communicate with the science probes and instruments. Based on the earlier Daedalus study, we estimate another factor of two to allow for these components. Pending the outcome of more detailed studies, it therefore appears that an overall science-related payload mass of ∼200 tonnes will be required. This paper is a submission of the Project Icarus Study Group.


Crawford I.A.,Birkbeck College London
JBIS - Journal of the British Interplanetary Society | Year: 2010

In this paper we outline the considerations required in order to select a target star system for the Icarus interstellar mission. It is considered that the maximum likely range for the Icarus vehicle will be 15 light-years, and a list is provided of all known stars within this distance range. As the scientific objectives of Icarus are weighted towards planetary science and astrobiology, a final choice of target star(s) cannot be made until we have a clearer understanding of the prevalence of planetary systems within 15 light-years of the Sun, and we summarise what is currently known regarding planetary systems within this volume. We stress that by the time an interstellar mission such as Icarus is actually undertaken, astronomical observations from the solar system will have provided this information. Finally, given the high proportion of multiple star systems within 15 lightyears (including the closest of all stars to the Sun in the a Centauri system), we stress that a flexible mission architecture, able to visit stars and accompanying planets within multiple systems, is desirable. This paper is a submission of the Project Icarus Study Group.

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