Biomedical subjects
C Hauert
Publications and source records attributed to C Hauert.
Reward and punishment.
Minigames capturing the essence of Public Goods experiments show that even in the absence of rationality assumptions, both punishment and reward will fail to bring about prosocial behavior. This result holds in particular for the well-known Ultimatum Game, which emerges as a special case. But reputation can induce fairness and cooperation in populations adapting through learning or imitation. Indeed, the inclusion of reputation effects in the corresponding dynamical models leads to the evolution of economically productive behavior, with agents contributing to the public good and either punishing those who do not or rewarding those who do. Reward and punishment correspond to two types of bifurcation with intriguing complementarity. The analysis suggests that reputation is essential for fostering social behavior among selfish agents, and that it is considerably more effective with punishment than with reward.
Fundamental clusters in spatial 2x2 games.
The notion of fundamental clusters is introduced, serving as a rule of thumb to characterize the statistical properties of the complex behaviour of cellular automata such as spatial 2 x 2 games. They represent the smallest cluster size determining the fate of the entire system. Checking simple growth criteria allows us to decide whether the cluster-individuals, e.g. some mutant family, are capable of surviving and invading a resident population. In biology, spatial 2 x 2 games have a broad spectrum of applications ranging from the evolution of cooperation and intraspecies competition to disease spread. This methodological study allows simple classifications and long-term predictions in various biological and social models to be made. For minimal neighbourhood types, we show that the intuitive candidate, a 3 x 3 cluster, turns out to be fundamental with certain weak limitations for the Moore neighbourhood but not for the Von Neumann neighbourhood. However, in the latter case, 2 x 2 clusters generally serve as reliable indicators to whether a strategy survives. Stochasticity is added to investigate the effects of varying fractions of one strategy present at initialization time and to discuss the rich dynamic properties in greater detail. Finally, we derive Liapunov exponents for the system and show that chaos reigns in a small region where the two strategies coexist in dynamical equilibrium.
Internally driven vs. externally cued movement selection: a study on the timing of brain activity.
Brain imaging studies in man and single cell recordings in monkey have suggested that medial supplementary motor areas (SMA) and lateral pre-motor areas (PMA) are functionally dissociated concerning their involvement in internally driven and externally cued movements. This dichotomy, however, seems to be relative rather than absolute. Here, we searched for further evidence of relative differences and aimed to determine by what aspect of brain activity (duration, strength, or both) these might be accounted for. Event-related potentials (ERPs) were recorded while healthy, right-handed subjects selected one of three possible right hand digit movements based either on 'internal' choice or 'external' cues. The results obtained from ERP mapping suggest that movement selection evokes the same electrical brain activity patterns in terms of surface potential configurations in the same order and at the same strength independent of the selection mode. These identical configurations, however, differed in their duration. Combined with the results of a distributed source localization procedure, our data are suggestive of longer lasting activity in SMA during the 'internal' and longer lasting activity in PMA during the 'external' condition. Our results confirm previous findings in showing that SMA and PMA are distinctively involved in the two tasks and that this functional dichotomy is relative rather than absolute but indicate that such a dissociation can result from differences in duration rather than pure strength of activation.
Self-organized criticality in a nutshell.
In order to gain insight into the nature of self-organized criticality (SOC), we present a minimal model exhibiting this phenomenon. In this analytically solvable model, the state of the system is fully described by a single-integer variable. The system organizes in its critical state without external tuning. We derive analytically the probability distribution of durations of disturbances propagating through the system. As required by SOC, this distribution is scale invariant and follows a power law over several orders of magnitude. Our solution also reproduces the exponential tail of the distribution due to finite size effects. Moreover, we show that large avalanches are suppressed when stabilizing the system in its critical state. Interestingly, avalanches are affected in a similar way when driving the system away from the critical state. With this model, we have reduced SOC dynamics to a leveling process as described by Ehrenfest's famous flea model.
Extending the Iterated Prisoner's Dilemma without Synchrony.
In biology altruistic behaviour of selfish individuals often can be modelled by the iterated Prisoner's Dilemma game (PD). If the opponents are caught repeatedly in this dilemma reciprocity may lead to cooperative strategies adopted by the individuals. In this article we present results from numerical simulations of the infinitely iterated stochastic alternating PD. First we investigate influences of the memory size on strategies in the alternating two player PD. We show that Firm but Fair is a strong strategy hardly affected by memory size and different values of the temptation to defect. Second we discuss successful strategies in the alternating N player N step memory PD. In this situation we focus on the stability of cooperative strategies and compare the results to experiments of predator inspection by sticklebacks carried out by Milinski and co-workers.Copyright 1998 Academic Press Limited