Uncovering the overlapping community structure of complex networks in nature and society

Many complex systems in nature and society can be described in terms of networks capturing the intricate web of connections among the units they are made of. A key question is how to interpret the global organization of such networks as the coexistence of their structural subunits (communities) associated with more highly interconnected parts. Identifying these a priori unknown building blocks (such as functionally related proteins, industrial sectors and groups of people) is crucial to the understanding of the structural and functional properties of networks. The existing deterministic methods used for large networks find separated communities, whereas most of the actual networks are made of highly overlapping cohesive groups of nodes. Here we introduce an approach to analysing the main statistical features of the interwoven sets of overlapping communities that makes a step towards uncovering the modular structure of complex systems. After defining a set of new characteristic quantities for the statistics of communities, we apply an efficient technique for exploring overlapping communities on a large scale. We find that overlaps are significant, and the distributions we introduce reveal universal features of networks. Our studies of collaboration, word-association and protein interaction graphs show that the web of communities has non-trivial correlations and specific scaling properties.Comment: The free academic research software, CFinder, used for the publication is available at the website of the publication: http://angel.elte.hu/clusterin

Global model analysis by parameter space partitioning

To model behavior, scientists need to know how models behave. This means learning what other behaviors a model can produce besides the one generated by participants in an experiment. This is a difficult problem because of the complexity of psychological models (e.g., their many parameters) and because the behavioral precision of models (e.g., interval-scale performance) often mismatches their testable precision in experiments, where qualitative, ordinal predictions are the norm. Parameter space partitioning is a solution that evaluates model performance at a qualitative level. There exists a partition on the model’s parameter space that divides it into regions that correspond to each data pattern. Three application examples demonstrate its potential and versatility for studying the global behavior of psychological models.Mark A. Pitt, Woojae Kim, Daniel J. Navarro, and Jay I. Myun

Quantum Aspects of Semantic Analysis and Symbolic Artificial Intelligence

Modern approaches to semanic analysis if reformulated as Hilbert-space problems reveal formal structures known from quantum mechanics. Similar situation is found in distributed representations of cognitive structures developed for the purposes of neural networks. We take a closer look at similarites and differences between the above two fields and quantum information theory.Comment: version accepted in J. Phys. A (Letter to the Editor

ERP evidence suggests executive dysfunction in ecstasy polydrug users

Background: Deficits in executive functions such as access to semantic/long-term memory have been shown in ecstasy users in previous research. Equally, there have been many reports of equivocal findings in this area. The current study sought to further investigate behavioural and electro-physiological measures of this executive function in ecstasy users. Method: Twenty ecstasy–polydrug users, 20 non-ecstasy–polydrug users and 20 drug-naïve controls were recruited. Participants completed background questionnaires about their drug use, sleep quality, fluid intelligence and mood state. Each individual also completed a semantic retrieval task whilst 64 channel Electroencephalography (EEG) measures were recorded. Results: Analysis of Variance (ANOVA) revealed no between-group differences in behavioural performance on the task. Mixed ANOVA on event-related potential (ERP) components P2, N2 and P3 revealed significant between-group differences in the N2 component. Subsequent exploratory univariate ANOVAs on the N2 component revealed marginally significant between-group differences, generally showing greater negativity at occipito-parietal electrodes in ecstasy users compared to drug-naïve controls. Despite absence of behavioural differences, differences in N2 magnitude are evidence of abnormal executive functioning in ecstasy–polydrug users

Response Selection in Visual Search: The Influence of Response Compatibility of Nontargets.

this article should be addressed to Peter A. Starreveld, Department of Cognitive Psychology, Vrije Universiteit, Van der Boechorststraat 1, 1081 BT Amsterdam, the Netherlands. E-mail: [email protected] Journal of Experimental Psychology: Copyright 2004 by the American Psychological Association, Inc. Human Perception and Performance 2004, Vol. 30, No. 1, 56 --78 0096-1523/04/$12.00 DOI: 10.1037/0096-1523.30.1.56 56 As discussed previously, flat slopes of search functions are interpreted as evidence showing that distractor elements in the corresponding experiments were only preattentively processed. Because identification of a display element involves attentive processing, two-stage theories of visual search predict that the identities of distractors should not affect the search time for a target in any search task in which flat search slopes are obtained. In the present study, this prediction was put to the tes

Amygdala and Ventrolateral Prefrontal Cortex Function during Anticipated Peer Evaluation in Pediatric Social Anxiety

1. Context. Amygdala and ventrolateral prefrontal cortex dysfunction manifests in adolescents with anxiety disorders when they view negatively-valenced stimuli in threatening contexts. Such fear-circuitry dysfunction may also manifest when anticipated social evaluation leads socially anxious adolescents to misperceive peers as threatening. 2. Objective. To determine whether photographs of negatively-evaluated smiling peers, viewed during anticipated evaluation, engage the amygdala and ventrolateral prefrontal cortex differentially in adolescents with and without social anxiety. 3. Design. Case-control study. 4. Setting. Government clinical research institute. 5. Participants. Fourteen adolescents with anxiety disorders associated with marked social concerns and 14 diagnosis-free adolescents, matched on sex, age, IQ, and socio-economic status. 6. Main Outcome Measure(s). Blood oxygenation level-dependent signal measured with event-related functional magnetic resonance imaging. Before and during neuroimaging scans, participants anticipating social evaluation completed peer- and self-appraisals. Event-related analyses were tailored to participants’ ratings of specific peers. 7. Results. Participants classified 40 pictures of same-age peers as ones they wanted to engage or not engage with for a social interaction. Anxious adolescents showed greater amygdala activation than healthy adolescents when anticipating evaluation from peers rated as undesired for an interaction. Viewing undesired peers engaged stronger positive amygdala-ventrolateral-prefrontal-cortex connectivity in anxious vs. healthy adolescents. 8. Conclusions. Anticipating social evaluation from negatively-perceived peers modulates amygdala and ventrolateral prefrontal cortex engagement differentially in anxious and healthy 3 adolescents. Amygdala and ventrolateral prefrontal cortex abnormalities in adolescent anxiety disorders are heightened in specific contexts of potential peer evaluation

Arming the Outlaws: On the Moral Limits of the Arms Trade

There is a general presumption against arming outlaw states. But can that presumption sometimes be overturned? The argument considered here maintains that outlaw states can have legitimate security interests, and that transferring weapons to these states can be an appropriate way of promoting those interests. Weapons enable governments to engage in wrongful oppression and aggression, but they also enable them to fend off predators in a manner that can be beneficial to their citizens. It clearly does not follow from the fact that a state is oppressive or aggressive that it will never be a victim of wrongful aggression itself, and while an outlaw state’s primary aim in repelling such aggression will often be the preservation of its own power, its defensive manoeuvres will sometimes also serve its citizens’ interests. In short, supplying weapons to outlaw states may sometimes contribute to the protection of innocents

The hypothetical consent objection to anti-natalism

Abstract: A very common but untested assumption is that potential children would consent to be exposed to the harms of existence in order to experience its benefits (if it were possible for us to ask and for them to respond). And so, would-be parents might appeal to the following view: Procreation is all-things-considered permissible, as it is morally acceptable for one to knowingly harm an unconsenting patient if one has good reasons for assuming her hypothetical consent—and procreators can indeed reasonably rely on some notion of hypothetical consent. I argue that this view is in error. My argument appeals to a consent-based version of anti-natalism advanced by Seana Valentine Shiffrin. Anti-natalism is the view that it is (almost) always wrong to bring people (and perhaps all sentient beings) into existence. While, like Shiffrin, I stop short of advocating a thoroughgoing anti-natalism, I nevertheless argue that procreators cannot appeal to hypothetical consent to justify exposing children to the harms of existence. I end by suggesting a more promising route by which this justification might be achieved