525 research outputs found
Processing of ultrasound in a bush cricket's brain
No full textThe processing and categorization of conspecific and heterospecific acoustic signals is an important task of the central nervous system. In orthopteran species, carrier frequency (besides temporal cues) is one of the major discriminators. In the bush cricket species Ancistrura nigrovittata Brunner von Wattenwyl (Phaneropteridae, Barbitistini), ultrasound has potentially different meanings and may elicit vastly different behaviours depending on the context it is perceived in. In the present study, data are presented of the morphology and neuronal responses of three local brain neurones (LBNs) that respond best to ultrasound. All neurones show dense arborizations in the lateral protocerebrum, where ascending interneurones terminate. The LBN2 and LBN9 neurones are entirely restricted to one side of the brain, whereas LBN5 crosses the midline, thereby linking both hemispheres. The response maxima for LBN2 overlap closely with the peak carrier frequencies found in a species-specific duet, which consists of sonic (16 kHz, male), as well as ultrasonic (2428 kHz, female) sound. By contrast, LBN9 responds only to ultrasound in the range of the female reply, whereas the male song induces exceptionally long-lasting inhibition. The LBN5 neurone shows strongest spike activity to a broad range of ultrasonic frequencies, as long as the pulse duration remains short. All three brain neurones respond to ultrasound in a unique way and may be involved in the shaping of different behavioural outcomes
Response differences of intersegmental auditory neurons recorded close to or far away from the presumed spike-generating zone
No full textIntracellular recordings may give valuable information about processing of a neuron and possibly its input from the network. Impalement with an electrode causes injury to the cell and depolarization from intrusion of extracellular fluid. Thus, penetration artefacts may contaminate recordings and conceal or even alter relevant information. These penetration artefacts may have the strongest impact close to the spike-generating zone near the dendrites. Recordings in axonal portions might therefore be less vulnerable while providing insufficient information about the synaptic input. In this study, we present data of five previously identified intersegmental auditory neurons of a bushcricket independently recorded in their dendrites (prothorax) and axon (brain). Generally, responses to acoustic pulses of the same parameter combination were similar within a neuronal class at the two recording sites. However, all neuronal classes showed significantly higher response variability and a tendency for higher spike activity when recorded in the dendrites. Unexpectedly, the combined activity of two neurons (Ascending Neurons 1 and 2) recorded in the brain provides a better fit to song recognition than when recorded in the thorax. Axonal recordings of T-shaped Neuron 1 revealed graded potentials originating in the brain and modulating its output in a potentially behaviourally relevant manner.German Science Foundation (DFG) [Stu 189/1-4
Frequency Processing at Consecutive Levels in the Auditory System of Bush Crickets (Tettigoniidae)
No full textWe asked how processing of male signals in the auditory pathway of the bush cricket Ancistrura nigrovittata (Phaneropterinae, Tettigoniidae) changes from the ear to the brain. From 37 sensory neurons in the crista acustica single elements (cells 8 or 9) have frequency tuning corresponding closely to the behavioral tuning of the females. Nevertheless, one-quarter of sensory neurons (approximately cells 9 to 18) excite the ascending neuron 1 (AN 1), which is best tuned to the male's song carrier frequency. AN1 receives frequency-dependent inhibition, reducing sensitivity especially in the ultrasound. When recorded in the brain, AN1 shows slightly lower overall activity than when recorded in the prothoracic ganglion close to the spike-generating zone. This difference is significant in the ultrasonic range. The first identified local brain neuron in a bush cricket (LBN1) is described. Its dendrites overlap with some of AN1-terminations in the brain. Its frequency tuning and intensity dependence strongly suggest a direct postsynaptic connection to AN1. Spiking in LBN1 is only elicited after summation of excitatory postsynaptic potentials evoked by individual AN1-action potentials. This serves a filtering mechanism that reduces the sensitivity of LBN1 and also its responsiveness to ultrasound as compared to AN1. Consequently, spike latencies of LBN1 are long (>30 ms) despite its being a second-order interneuron. Additionally, LBN1 receives frequency-specific inhibition, most likely further reducing its responses to ultrasound. This demonstrates that frequency-specific inhibition is redundant in two directly connected interneurons on subsequent levels in the auditory system. J. Comp. Neurol. 518:3101-3116, 2010. (C) 2010 Wiley-Liss, Inc
Temporal processing properties of auditory DUM neurons in a bush-cricket
No full textInsects with ears process sounds and respond to conspecific signals or predator cues. Axons of auditory sensory cells terminate in mechanosensory neuropils from which auditory interneurons project into (brain-) areas to prepare response behaviors. In the prothoracic ganglion of a bush-cricket, a cluster of local DUM (dorsal unpaired median) neurons has recently been described and constitutes a filter bank for carrier frequency. Here, we demonstrate that these neurons also constitute a filter bank for temporal patterns. The majority of DUM neurons showed pronounced phasic-tonic responses. The transitions from phasic to tonic activation had different time constants in different DUM neurons. Time constants of the membrane potential were shorter in most DUM neurons than in auditory sensory neurons. Patterned stimuli with known behavioral relevance evoked a broad range of responses in DUM neurons: low-pass, band-pass, and high-pass characteristics were encountered. Temporal and carrier frequency processing were not correlated. Those DUM neurons producing action potentials showed divergent processing of temporal patterns when the graded potential or the spiking was analyzed separately. The extent of membrane potential fluctuations mimicking the patterned stimuli was different between otherwise similarly responding neurons. Different kinds of inhibition were apparent and their relevance for temporal processing is discussed
A Critique of Computable General Equilibrium Models for Trade Policy Analysis
No full textThe paper will deal in turn with three sets of modelling issues: the question of 'data'; the 'micro' problem of specifying market behaviour, and the. 'macro' issue of 'closing' the models in aggregate. I will conclude with some suggestions for future research. The basic theme of the paper is this: CGE modelling is essentially a conservative or 'neoclassical' scientific endeavour, and exhibits the strengths and weaknesses of neoclassicism. And as for the recent injection of apparently nonneoclassical imperfect competition or industrial organization (IO) concepts into CGE, though, as an 10 specialist myself I certainly welcome this in principle, I have doubts about the usefulness of the practice.International Relations/Trade,
Distributed human computation framework for linked data co-reference resolution
No full textDistributed Human Computation (DHC) is a technique used to solve computational problems by incorporating the collaborative effort of a large number of humans. It is also a solution to AI-complete problems such as natural language processing. The Semantic Web with its root in AI is envisioned to be a decentralised world-wide information space for sharing machine-readable data with minimal integration costs. There are many research problems in the Semantic Web that are considered as AI-complete problems. An example is co-reference resolution, which involves determining whether different URIs refer to the same entity. This is considered to be a significant hurdle to overcome in the realisation of large-scale Semantic Web applications. In this paper, we propose a framework for building a DHC system on top of the Linked Data Cloud to solve various computational problems. To demonstrate the concept, we are focusing on handling the co-reference resolution in the Semantic Web when integrating distributed datasets. The traditional way to solve this problem is to design machine-learning algorithms. However, they are often computationally expensive, error-prone and do not scale. We designed a DHC system named iamResearcher, which solves the scientific publication author identity co-reference problem when integrating distributed bibliographic datasets. In our system, we aggregated 6 million bibliographic data from various publication repositories. Users can sign up to the system to audit and align their own publications, thus solving the co-reference problem in a distributed manner. The aggregated results are published to the Linked Data Cloud
Acceptance conditions in automated negotiation
No full textIn every negotiation with a deadline, one of the negotiating parties has to accept an offer to avoid a break off. A break off is usually an undesirable outcome for both parties, therefore it is important that a negotiator employs a proficient mechanism to decide under which conditions to accept. When designing such conditions one is faced with the acceptance dilemma: accepting the current offer may be suboptimal, as better offers may still be presented. On the other hand, accepting too late may prevent an agreement from being reached, resulting in a break off with no gain for either party. Motivated by the challenges of bilateral negotiations between automated agents and by the results and insights of the automated negotiating agents competition (ANAC), we classify and compare state-of-the-art generic acceptance conditions. We focus on decoupled acceptance conditions, i.e. conditions that do not depend on the bidding strategy that is used. We performed extensive experiments to compare the performance of acceptance conditions in combination with a broad range of bidding strategies and negotiation domains. Furthermore we propose new acceptance conditions and we demonstrate that they outperform the other conditions that we study. In particular, it is shown that they outperform the standard acceptance condition of comparing the current offer with the offer the agent is ready to send out. We also provide insight in to why some conditions work better than others and investigate correlations between the properties of the negotiation environment and the efficacy of acceptance conditions.MediamaticsElectrical Engineering, Mathematics and Computer Scienc
Reimagining the Golem: The Creation and Development of Daniel Silva’s Spiritually-Motivated Protagonist, Gabriel Allon
No full textDaniel Silva’s legendary hero, Gabriel Allon, is intended to embody the concepts of justice, order and spiritually-motivated retribution and has been created to combat threats against the contemporary social order via a combination of guile, ruthlessness and heroism. He is also designed to be unhindered by any physical, emotional or financial restrictions and can therefore exercise his power (against any person, organisation or situation) in the pursuit of an ideology which defines and promotes the political intentions and the cultural influences of his author.
This thesis challenges the figure of Gabriel Allon by arguing firstly, that he is in fact a highly ambivalent, morally problematic figure and secondly, in demonstrating where elements of real-life (adapted by the author to support his ideological stance) have undermined the reliability of the narrative. The thesis has also examined some of the political sub-texts employed by the author to question whether his methodology is serving to enhance the plausibility of the fiction or whether it is embedding dangerously subjective depictions of counter-terrorism into the reader’s consciousness
Filterung artspezifischer Gesangsparameter durch Interneurone im Gehirn einer Laubheuschrecke
No full textIn dieser Doktorarbeit werden zum ersten Mal Daten
von identifizierten Interneuronen im Gehirn einer
Laubheuschrecke dargestellt. Intrazelluläre Ableitungen
wurden an einzelnen Zellen in der Laubheuschrecke
Ancistrura nigrovittata (Brunner von Wattenwyl,
1878) durchgeführt und auf ihre Filtereigenschaften in
Bezug auf Trägerfrequenz, Intensität und
Amplitudenmodulation von akustischen Reizen hin
untersucht. Dabei wurde besonderes Augenmerk auf die
Verarbeitung von artspezifischen Gesangsparametern
gelegt, für welche spezifische Verhaltensleistungen
bekannt sind.
Die Aktivität von fünf verschiedenen Klassen schon
bekannter aszendierender Nervenzellen in den axonalen
Hirnverzweigungen konnte mit zuvor beschriebenen Daten
aus der dendritischen Region im prothorakalen Ganglion
verglichen werden. Die an beiden Ableitorten gefundenen
physiologischen Eigenschaften sind in weiten Teilen
sehr ähnlich (größte Übereinstimmung bei AN3), obwohl
sich für einige Interneurone auch Unterschiede
aufzeigen ließen. Diese sind z.B.:
(i) Filtereigenschaften von AN1 und AN2 auf einige
Pulsdauern, die in Kombination sehr nah mit dem
phonotaktischen Verhalten der Weibchen dieser Art
korrelieren
(ii) graduierte Potenziale im Axon von TN1, die bei
simultanem Auftreten eines Aktionspotenzials dessen
Amplitude durch Summation graduell erhöhen
(iii) eine physiologische und morphologische
Beschreibung der Hirnterminalien einer bis dato
unbekannten aszendierende Nervenzelle (ANx), welche an
der Verarbeitung von Ultraschall beteiligt ist.
Eigenschaften von insgesamt zehn verschiedenen Typen
lokaler auditorischer Hirnneurone werden beschrieben,
die unterschiedliche Mechanismen der Verarbeitung von
akustischen Signalen aufzeigen, wobei einige
Verarbeitungsprozesse schon vom Thorax bekannt sind und
eine erstaunlich hohe Redundanz aufweisen. Diese sind
z.B.:
(i) ein Spike-Frequenzfilter und eine redundante
frequenzspezifische Inhibition von LBN1, dessen
resultierende Eigenschaften zu dem Antwortverhalten
eines Weibchens dieser Art eine größere Übereinstimmung
zeigen, als die Aktivität des zu LBN1 präsynaptischen
Neurons (AN1)
(ii) eine engbandige Abstimmung der Aktivität von LBN2
auf die artspezifischen Signale beider Geschlechter -
ein Typ von Informationskanal , der im Individuum
arteigene Kommunikation im nahen Umfeld erkennt
(iii) die Verarbeitung auditorischer Stimuli in
nacheinander geschalteten Verarbeitungsebenen bis zu
einem Interneuron dritter Ordnung, wobei auch ein
Wechsel von erregenden zu hemmenden Einflüssen zu
finden ist
(iv) eine größere Varietät von selektiver Verarbeitung
von Ultraschall und zeitlichen Parametern, als es bei
thorakalen Neuronen zu finden ist
(v) eine sekundäre Aktivität, welche der Stimulation
mit einer Latenz von ca. 600 ms folgt und graduierte
Potenziale mit bemerkenswert hohen Zeitkonstanten von
mehreren hundert Millisekunden.
Viele dieser Verarbeitungsmechanismen führen zu einer
größeren Übereinstimmung der Nervenzellaktivität im
Gehirn mit dem artspezifischen Verhalten, als die zuvor
im Thorax gefundenen Mechanismen.In this doctoral thesis intracellular recordings of
identified auditory neurons in the brain of a bush
cricket are presented for the first time. Single cell
recordings were carried out in the species
Ancistrura nigrovittata (Brunner von Wattenwyl,
1878) with special emphasis on filtering properties for
the conspecific song. The coding of carrier frequency,
intensity and temporal pattern was examined in local
brain neurons and in intersegmental neurons for a
comparison with the behavioural responses to these
parameters.
Spike activity of five types of ascending
intersegmental neurons was acquired from the axonal
terminals, which allowed a correlation to earlier
results obtained from the dendrites. The response
characteristics found in both recording sites are
widely similar (closest in AN3), although differences
have been observed. These are e.g.:
(i) filter properties in the spike activity of AN1 and
AN2 to some pulse durations, which closely correlate to
the female behaviour
(ii) graded potentials in TN1 s axon with the
capability to facilitate the amplitude of action
potentials in a graded manner close to the presynaptic
output site
(iii) a physiological and a morphological description
in the brain, of a so far unknown intersegmental neuron
(ANx) that processes ultrasound stimuli.
A characterisation of ten types of local auditory brain
neurons is given, whereby novel as well as known
response properties with a surprisingly high degree of
redundant filter mechanisms are found. These are
e.g.:
(i) a spike frequency filter and a redundant frequency
dependent inhibition in LBN1 resulting in a response
that has a closer correlation to the female behaviour
than found in the spiking of its presynaptic neuron
(AN1)
(ii) the narrowly tuned activity of LBN2 to conspecific
signals of both sexes - representing a channel that
indicates species specific communication in the
surrounding area
(iii) the tracing of auditory processing on subsequent
levels up to a third order interneuron including a
switch of excitation to inhibition
(iv) a greater variety of selective responses to
ultrasonic stimuli and temporal parameters than
described for thoracic neurons
(v) secondary spike activity following stimulation with
a latency of ca. 600 ms and graded potentials
exhibiting remarkably long time constants of several
hundred milliseconds.
Several of these mechanisms lead to a closer
correspondence of neuronal activity to species specific
behaviour than found in the thorax
The politics of journalistic creativity: expressiveness, authenticity and de-authorization
No full textThis article begins with the assertion that creativity in journalism has moved from being a matter of guile and ingenuity to being about expressiveness, and that this reflects a broader cultural shift from professional expertise to the authenticity of personal expression as dominant modes of valorization. It then seeks to unpack the normative baggage that underpins the case for creativity in the cultural industries. First, there is a prioritization of agency, which does not stand up against the phenomenological argument that we do not own our own practices. Second, creative expression is not necessarily more free, simply alternately structured. As with Judith Butler’s performativity model, contemporary discourses of creativity assume it to have a unique quality by which it eludes determination (relying on tropes of fluidity), whereas it can be countered that it is in spontaneous, intuitive practice that we are at our least agencical. Third, the article argues against the idea that by authorizing journalists (and audiences) to express themselves, creativity is democratizing, since the always-already nature of recognition means that subjects can only voice their position within an established terrain rather than engage active positioning
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