Mechanosensory interactions drive collective behaviour in Drosophila.

Collective behaviour enhances environmental sensing and decision-making in groups of animals. Experimental and theoretical investigations of schooling fish, flocking birds and human crowds have demonstrated that simple interactions between individuals can explain emergent group dynamics. These findings indicate the existence of neural circuits that support distributed behaviours, but the molecular and cellular identities of relevant sensory pathways are unknown. Here we show that Drosophila melanogaster exhibits collective responses to an aversive odour: individual flies weakly avoid the stimulus, but groups show enhanced escape reactions. Using high-resolution behavioural tracking, computational simulations, genetic perturbations, neural silencing and optogenetic activation we demonstrate that this collective odour avoidance arises from cascades of appendage touch interactions between pairs of flies. Inter-fly touch sensing and collective behaviour require the activity of distal leg mechanosensory sensilla neurons and the mechanosensory channel NOMPC. Remarkably, through these inter-fly encounters, wild-type flies can elicit avoidance behaviour in mutant animals that cannot sense the odour--a basic form of communication. Our data highlight the unexpected importance of social context in the sensory responses of a solitary species and open the door to a neural-circuit-level understanding of collective behaviour in animal groups.

Quantifying Accuracy Improvement in Sets of Pooled Judgments: Does Dialectical Bootstrapping Work?

Galton (1907) first demonstrated the "wisdom of crowds" phenomenon by averaging independent estimates of unknown quantities given by many individuals. Herzog and Hertwig (2009; hereafter H&H in Psychological Science) showed that individuals' own estimates can be improved by asking them to make two estimates at separate times and averaging them. H&H claimed to observe far greater improvement in accuracy when participants received "dialectical" instructions to consider why their first estimate might be wrong before making their second estimates than when they received standard instructions. We reanalyzed H&H's data using measures of accuracy that are unrelated to the frequency of identical first and second responses and found that participants in both conditions improved their accuracy to an equal degree.

INdividual SUrveys in RAllies (INSURA), A new tool for exploring transnational activism?

Prior the middle of the 90', interviewing participants in protest events was quiet rare. INdividual SUrveys in RAllies (INSURA) did enter the social researcher's usual toolkit only in the following decade after Favre, Fillieule and Mayer (1997) conducted such a survey with as a primary ambition to build a solid methodological framework that could be subsequently applied by other researchers. After some years of intensive use of INSURA, one is entitled to wonder whether that technique has fulfilled social researchers' hopes or not. In that paper, results of a collective work on alter-global rallies in Evian and Saint- Denis are used to answer three interrelated questions. Firstly, some basic methodological questions about how to collect data on crowds are adressed. What are the specific constraints of interviewing people at the very moment they are "expressing" a political opinion? What specific constraints result from the morphology of the covered events, that is to say, how to build a valid sampling frame? The authors then turn to a more general point about the questions that can be solved, or not, using that technique. Secondly it is the strenghts and weaknesses of INSURA in exploring the transnational dimension of alter global protests that is adressed. The authors show that INSURA is certainly well suited to explore the demographics of alter-global events, as well as relational networks of individuals and multiple belongings. On the contrary, it is assumed that organization networks and movement's boundaries are far more difficult to explore through that method, a fact that seriously limits international cross comparisons of events and movements based on that tool.

Injury pattern of the Flash-Ball, a less-lethal weapon used for law enforcement: report of two cases and review of the literature.

Less-lethal weapons are used in law enforcement to neutralize combative individuals and to disperse riot crowds. Local police recently used such an impact weapon, the Flash-Ball, in two different situations. This gun fires large rubber bullets with kinetic energies around 200 J. Although it is designed to avoid skin penetration, impacts at such energies may still create major trauma with associated severe injuries to internal organs. This is a report of 2 patients shot with the Flash-Ball who required medical attention. One could be discharged quickly, but the other required hospitalization for heart and lung contusion. Both patients required advanced investigations including computed tomography (CT) scan. The medical literature on injuries induced by less-lethal impact weapons is reviewed. Impacts from the Flash-Ball can cause significant injury to internal organs, even without penetration. Investigations as for other high-energy blunt traumas are called for in these cases.