Spatio-temporal pattern recognizers using spiking neurons and spike-timing-dependent plasticity.

It has previously been shown that by using spike-timing-dependent plasticity (STDP), neurons can adapt to the beginning of a repeating spatio-temporal firing pattern in their input. In the present work, we demonstrate that this mechanism can be extended to train recognizers for longer spatio-temporal input signals. Using a number of neurons that are mutually connected by plastic synapses and subject to a global winner-takes-all mechanism, chains of neurons can form where each neuron is selective to a different segment of a repeating input pattern, and the neurons are feed-forwardly connected in such a way that both the correct input segment and the firing of the previous neurons are required in order to activate the next neuron in the chain. This is akin to a simple class of finite state automata. We show that nearest-neighbor STDP (where only the pre-synaptic spike most recent to a post-synaptic one is considered) leads to "nearest-neighbor" chains where connections only form between subsequent states in a chain (similar to classic "synfire chains"). In contrast, "all-to-all spike-timing-dependent plasticity" (where all pre- and post-synaptic spike pairs matter) leads to multiple connections that can span several temporal stages in the chain; these connections respect the temporal order of the neurons. It is also demonstrated that previously learnt individual chains can be "stitched together" by repeatedly presenting them in a fixed order. This way longer sequence recognizers can be formed, and potentially also nested structures. Robustness of recognition with respect to speed variations in the input patterns is shown to depend on rise-times of post-synaptic potentials and the membrane noise. It is argued that the memory capacity of the model is high, but could theoretically be increased using sparse codes

A Spiking Self-Organising Map Combining STDP, Oscillations and Continuous Learning

Open Access article EPSRC EP/C010841/1, EP/J004561/

ConversationPiece II: Displaced and Rehacked

Abstract: Conversations are amazing! Although we usually find the experience enjoyable and even relaxing, when one considers the difficulties of simultaneously generating sig- nals that convey an intended message while at the same time trying to understand the messages of another, then the pleasures of conversation may seem rather surprising. We manage to communicate with each other without knowing quite what will happen next. We quickly manufacture precisely timed sounds and gestures on the fly, which we exchange with each other without clashing—even managing to slip in some imita- tions as we go along! Yet usually meaning is all we really notice. In the Conversa- tionPiece project, we aim to transform conversations into musical sounds using neuro-inspired technology to expose the amazing world of sounds people create when talking with others. Sounds from a microphone are separated into different fre- quency bands by a computer-simulated “ear” (more precisely “basilar membrane”) and analyzed for tone onsets using a lateral-inhibition network, similar to some cor- tical neural networks. The detected events are used to generate musical notes played on a synthesizer either instantaneously or delayed. The first option allows for ex- changing timed sound events between two speakers with a speech-like structure, but without conveying (much) meaning. Delayed feedback further allows self-exploration of one’s own speech. We discuss the current setup (ConversationPiece version II), in- sights from first experiments, and options for future applications

Choosing party leaders: Anglophone democracies, British parties and the limits of comparative politics

Since 1965, Britain’s major political parties have radically, and repeatedly, changed the ways in which they choose their leaders. Building on a recent comparative study of party leadership selection in the five principal Anglophone (‘Westminster’) parliamentary democracies (Cross and Blais, 2012a), this article first outlines a theoretical framework that purports to explain why the major parties in three of those countries, including Britain, have adopted such reform. It then examines why five major British parties have done so since 1965. It argues that, while Cross and Blais’ study makes a significant contribution to our knowledge and understanding of processes of party leadership selection reform in Anglophone parliamentary democracies, it has limited explanatory power when applied to changes enacted by the major parties in modern and contemporary Britain. Instead, the adoption of such reform in the British context is ultimately best understood and explained by examining both the internal politics and external circumstances of individual parties

A robust sound perception model suitable for neuromorphic implementation

Coath M, Sheik S, Chicca E, Indiveri G, Denham S, Wennekers T. A robust sound perception model suitable for neuromorphic implementation. Neuromorphic Engineering. 2014;7(278):1-10.We have recently demonstrated the emergence of dynamic feature sensitivity through exposure to formative stimuli in a real-time neuromorphic system implementing a hybrid analog/digital network of spiking neurons. This network, inspired by models of auditory processing in mammals, includes several mutually connected layers with distance-dependent transmission delays and learning in the form of spike timing dependent plasticity, which effects stimulus-driven changes in the network connectivity. Here we present results that demonstrate that the network is robust to a range of variations in the stimulus pattern, such as are found in naturalistic stimuli and neural responses. This robustness is a property critical to the development of realistic, electronic neuromorphic systems. We analyze the variability of the response of the network to “noisy” stimuli which allows us to characterize the acuity in information-theoretic terms. This provides an objective basis for the quantitative comparison of networks, their connectivity patterns, and learning strategies, which can inform future design decisions. We also show, using stimuli derived from speech samples, that the principles are robust to other challenges, such as variable presentation rate, that would have to be met by systems deployed in the real world. Finally we demonstrate the potential applicability of the approach to real sounds

Chamber basis of the Orlik-Solomon algebra and Aomoto complex

We introduce a basis of the Orlik-Solomon algebra labeled by chambers, so called chamber basis. We consider structure constants of the Orlik-Solomon algebra with respect to the chamber basis and prove that these structure constants recover D. Cohen's minimal complex from the Aomoto complex.Comment: 16 page

Tales of the unexpected: the selection of British party leaders since 1963

Jeremy Corbyn’s election as Leader of the Labour Party in 2015 stunned observers and practitioners of British politics alike. In this article, we first outline a theoretical framework that purports to explain why political parties operating in parliamentary systems choose the leaders they do. We then examine 32 leadership successions involving five major British parties since 1963, and note that many of these were unexpected, in that they were triggered by unforeseen circumstances, such as the sudden death or resignation of the incumbent. Examining each party in turn, we briefly explain why the winners won and identify at least eight cases (a quarter of our sample) where a candidate widely expected to prevail at the outset was ultimately defeated by a ‘dark horse’, ‘second favourite’ or even ‘rank outsider’. Of these, Corbyn’s election in 2015 was the most unexpected and, consistent with the findings of studies of party leadership conventions in other parliamentary systems, namely Canada and Spain, suggests that ideological and policy concerns are sometimes more important than considerations of party unity and electability, especially when a leadership contest is dominated by party activists

A state of cities or a city-state? Metro-bound commuters and the distribution of people and employment in a monocentric city-region

This thesis investigates the relationship between metro-bound commuting and regional development; asking whether over time metro-bound commuting results in a redistribution of economic functions and the reorganisation of the city-region into a more functionally polycentric urban structure. There is an increasing number of metropolitan workers living in rural or non-metropolitan areas, referred to as metro-bound commuters in this research. At the same time, there are concerns regarding the concentration of prosperity in major cities and diminishing opportunities for high-quality employment in regional cities and towns. This change has been seen as a consequence of the transition to service- and knowledge-based employment in developed economies. Previous research has indicated that there are consumption-based regional employment benefits from metro-bound commuting. This study extends these findings by assessing the quality of employment generated and the impact on regional communities as a result of metro-bound commuting. The outcome of this assessment indicates whether metro-bound commuting is a precursor to functional polycentrism, which has been promoted as a more equitable and efficient city-region morphology than monocentrism, or solely population-based polycentrism. The research uses mixed methods to investigate the regional employment effects of metro-bound commuting to Melbourne, Australia from its regional hinterlands. Census data and the results of a survey of commuters provide the basis for qualitative analyses. Interviews with commuters and representatives from government provide further insights into metro-bound commuting and its impacts on individuals and regional communities. The survey and interviews also provide new insights into the relationship between metro-bound commuting and regional employment through the effects of commuters' human capital and their households. The outcomes of the qualitative and quantitative analyses inform the analysis of local, state and commonwealth government policy and infrastructure proposals relating to regional economies and population. The results of this investigation demonstrate that the number of metro-bound commuters residing in a regional settlement is correlated with the population of regional settlements and the inverse square of the settlement's distance from the metropolis. Population growth as a result of metro-bound commuting may be increasing expenditure and employment in regional settlements, but the results of the research indicate that there is not redistribution of higher-value knowledge-based employment. Therefore, this research does not find evidence that metro-bound commuting facilitates functional polycentrism. Such travel is more appropriately described as population-based polycentrism or the suburbanisation of regional settlements. Given this finding, the current government focus on population distribution facilitated by large scale infrastructure projects is questioned. The central conclusion of the thesis is that governments should assess policy and infrastructure proposals on their capacity to redistribute economic functions and employment opportunities, not population

Poisson-de Rham homology of hypertoric varieties and nilpotent cones

We prove a conjecture of Etingof and the second author for hypertoric varieties, that the Poisson-de Rham homology of a unimodular hypertoric cone is isomorphic to the de Rham cohomology of its hypertoric resolution. More generally, we prove that this conjecture holds for an arbitrary conical variety admitting a symplectic resolution if and only if it holds in degree zero for all normal slices to symplectic leaves. The Poisson-de Rham homology of a Poisson cone inherits a second grading. In the hypertoric case, we compute the resulting 2-variable Poisson-de Rham-Poincare polynomial, and prove that it is equal to a specialization of an enrichment of the Tutte polynomial of a matroid that was introduced by Denham. We also compute this polynomial for S3-varieties of type A in terms of Kostka polynomials, modulo a previous conjecture of the first author, and we give a conjectural answer for nilpotent cones in arbitrary type, which we prove in rank less than or equal to 2.Comment: 25 page

Definition of the σW regulon of Bacillus subtilis in the absence of stress

Bacteria employ extracytoplasmic function (ECF) sigma factors for their responses to environmental stresses. Despite intensive research, the molecular dissection of ECF sigma factor regulons has remained a major challenge due to overlaps in the ECF sigma factor-regulated genes and the stimuli that activate the different ECF sigma factors. Here we have employed tiling arrays to single out the ECF σW regulon of the Gram-positive bacterium Bacillus subtilis from the overlapping ECF σX, σY, and σM regulons. For this purpose, we profiled the transcriptome of a B. subtilis sigW mutant under non-stress conditions to select candidate genes that are strictly σW-regulated. Under these conditions, σW exhibits a basal level of activity. Subsequently, we verified the σW-dependency of candidate genes by comparing their transcript profiles to transcriptome data obtained with the parental B. subtilis strain 168 grown under 104 different conditions, including relevant stress conditions, such as salt shock. In addition, we investigated the transcriptomes of rasP or prsW mutant strains that lack the proteases involved in the degradation of the σW anti-sigma factor RsiW and subsequent activation of the σW-regulon. Taken together, our studies identify 89 genes as being strictly σW-regulated, including several genes for non-coding RNAs. The effects of rasP or prsW mutations on the expression of σW-dependent genes were relatively mild, which implies that σW-dependent transcription under non-stress conditions is not strictly related to RasP and PrsW. Lastly, we show that the pleiotropic phenotype of rasP mutant cells, which have defects in competence development, protein secretion and membrane protein production, is not mirrored in the transcript profile of these cells. This implies that RasP is not only important for transcriptional regulation via σW, but that this membrane protease also exerts other important post-transcriptional regulatory functions