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Concept: Reciprocity


The strong reciprocity model of the evolution of human cooperation has gained some acceptance, partly on the basis of support from experimental findings. The observation that unfair offers in the ultimatum game are frequently rejected constitutes an important piece of the experimental evidence for strong reciprocity. In the present study, we have challenged the idea that the rejection response in the ultimatum game provides evidence of the assumption held by strong reciprocity theorists that negative reciprocity observed in the ultimatum game is inseparably related to positive reciprocity as the two sides of a preference for fairness. The prediction of an inseparable relationship between positive and negative reciprocity was rejected on the basis of the results of a series of experiments that we conducted using the ultimatum game, the dictator game, the trust game, and the prisoner’s dilemma game. We did not find any correlation between the participants' tendencies to reject unfair offers in the ultimatum game and their tendencies to exhibit various prosocial behaviors in the other games, including their inclinations to positively reciprocate in the trust game. The participants' responses to postexperimental questions add support to the view that the rejection of unfair offers in the ultimatum game is a tacit strategy for avoiding the imposition of an inferior status.

Concepts: Game theory, Hypothesis, The Evolution of Cooperation, Prisoner's dilemma, Dictator game, Ultimatum game, Experimental economics, Reciprocity


Disorderly resolution of conflict is costly, whereas orderly resolution by consent rules enables quick settlement. However, it is unclear whether non-human animals can make and observe rules to resolve conflict without aggression. Here we report a new behavioral paradigm for mice: a modified two-armed maze that uses wireless electrical brain stimulation as reward. First, the mice were individually operant-trained to initiate and then receive the reward at the signaled arm. Next, two mice were coupled and had to cooperate to initiate reward but then to compete over reward allocation. Mice develop and observe a rule of reward zone allocation that increases the total amount of reward and reward equity between the pair. In the mutual rule-observance behavior, positive reciprocity and tolerance to the other’s violation are also observed. These findings suggest that rodents can learn to make and observe rules to resolve conflict, enhancing long-term benefit and payoff equity.

Concepts: Psychology, Observation, Philosophy of science, Behavior, Motivation, Reciprocity, Brain stimulation reward, The Reward


Purpose: To develop a transdisciplinary conceptualization of social belonging that could be used to guide measurement approaches aimed at evaluating the effectiveness of community-based programs for people with disabilities. Method: We conducted a narrative, scoping review of peer reviewed English language literature published between 1990 and July 2011 using multiple databases, with “sense of belonging” as a key search term. The search engine ranked articles for relevance to the search strategy. Articles were searched in order until theoretical saturation was reached. We augmented this search strategy by reviewing reference lists of relevant papers. Results: Theoretical saturation was reached after 40 articles; 22 of which were qualitative accounts. We identified five intersecting themes: subjectivity; groundedness to an external referent; reciprocity; dynamism and self-determination. Conclusion: We define a sense of belonging as a subjective feeling of value and respect derived from a reciprocal relationship to an external referent that is built on a foundation of shared experiences, beliefs or personal characteristics. These feelings of external connectedness are grounded to the context or referent group, to whom one chooses, wants and feels permission to belong. This dynamic phenomenon may be either hindered or promoted by complex interactions between environmental and personal factors. [Box: see text].

Concepts: Philosophy of language, Semantics, Review, Search engine optimization, Reciprocity, Searching, Reference, Reciprocal


Recent research has explored the spatiotemporal modulation of permittivity to break Lorentz reciprocity in a manner compatible with integrated-circuit fabrication. However, permittivity modulation is inherently weak and accompanied by loss due to carrier injection, particularly at higher frequencies, resulting in large insertion loss, size, and/or narrow operation bandwidths. Here, we show that the presence of absorption in an integrated electronic circuit may be counter-intuitively used to our advantage to realize a new generation of magnet-free non-reciprocal components. We exploit the fact that conductivity in semiconductors provides a modulation index several orders of magnitude larger than permittivity. While directly associated with loss in static systems, we show that properly synchronized conductivity modulation enables loss-free, compact and extremely broadband non-reciprocity. We apply these concepts to obtain a wide range of responses, from isolation to gyration and circulation, and verify our findings by realizing a millimeter-wave (25 GHz) circulator fully integrated in complementary metal-oxide-semiconductor technology.Optical non-reciprocity achieved through refractive index modulation can have its challenges and limitations. Here, Dinc et al. introduce the concept of non-reciprocity based on synchronized spatio-temporal modulation of conductivity to achieve different types of non-reciprocal functionality.

Concepts: Electromagnetism, Fundamental physics concepts, Refractive index, Electromagnetic radiation, Electrical conductivity, Reciprocity, Circulator


Lorentz reciprocity is a fundamental characteristic of the vast majority of electronic and photonic structures. However, non-reciprocal components such as isolators, circulators and gyrators enable new applications ranging from radio frequencies to optical frequencies, including full-duplex wireless communication and on-chip all-optical information processing. Such components today dominantly rely on the phenomenon of Faraday rotation in magneto-optic materials. However, they are typically bulky, expensive and not suitable for insertion in a conventional integrated circuit. Here we demonstrate magnetic-free linear passive non-reciprocity based on the concept of staggered commutation. Commutation is a form of parametric modulation with very high modulation ratio. We observe that staggered commutation enables time-reversal symmetry breaking within very small dimensions (λ/1,250 × λ/1,250 in our device), resulting in a miniature radio-frequency circulator that exhibits reduced implementation complexity, very low loss, strong non-reciprocity, significantly enhanced linearity and real-time reconfigurability, and is integrated in a conventional complementary metal-oxide-semiconductor integrated circuit for the first time.

Concepts: Electromagnetism, Optics, Fundamental physics concepts, Symmetry, Group, Reciprocity, Circulator


To demonstrate causal relationships between brain and behavior, investigators would like to guide brain stimulation using measurements of neural activity. Particularly promising in this context are electroencephalography (EEG) and transcranial electrical stimulation (TES), as they are linked by a reciprocity principle which, despite being known for decades, has not led to a formalism for relating EEG recordings to optimal stimulation parameters. Here we derive a closed-form expression for the TES configuration that optimally stimulates (i.e., targets) the sources of recorded EEG, without making assumptions about source location or distribution. We also derive a duality between TES targeting and EEG source localization, and demonstrate that in cases where source localization fails, so does the proposed targeting. Numerical simulations with multiple head models confirm these theoretical predictions and quantify the achieved stimulation in terms of focality and intensity. We show that constraining the stimulation currents automatically selects optimal montages that involve only a few (4-7) electrodes, with only incremental loss in performance when targeting focal activations. The proposed technique allows brain scientists and clinicians to rationally target the sources of observed EEG and thus overcomes a major obstacle to the realization of individualized or closed-loop brain stimulation.

Concepts: Scientific method, Brain, Electroencephalography, Philosophy of science, Electrode, Metaphysics, Target Corporation, Reciprocity


Nearly all quantitative studies examining the association between the division of housework and gender ideology have found that gender egalitarianism results in less housework for wives, more for husbands, and more equal sharing of housework by couples. However, a few studies suggest housework has a nontrivial influence on gender ideology. An overreliance on single-direction, single-equation regression models and cross-sectional data has limited past research from making strong claims about the causal relationship between gender ideology and housework. We use data on married couples from Waves 1 and 2 of the National Survey of Families and Households and nonrecursive simultaneous equation models to assess the causal relationship between housework and gender ideology. Results show a mutual and reciprocal relationship between the division of housework and gender ideology for both husbands' and wives'. Reciprocity is strongest for husbands while for wives the relationship is partially indirect and mediated through their husbands' gender ideologies.

Concepts: Family, Marriage, Causality, Sociology, Husband, Reciprocity, Reciprocal, Feminism


Many interactions in modern human societies are among strangers. Explaining cooperation in such interactions is challenging. The two most prominent explanations critically depend on individuals' willingness to punish defectors: In models of direct punishment, individuals punish antisocial behavior at a personal cost, whereas in models of indirect reciprocity, they punish indirectly by withholding rewards. We investigate these competing explanations in a field experiment with real-life interactions among strangers. We find clear evidence of both direct and indirect punishment. Direct punishment is not rewarded by strangers and, in line with models of indirect reciprocity, is crowded out by indirect punishment opportunities. The existence of direct and indirect punishment in daily life indicates the importance of both means for understanding the evolution of cooperation.

Concepts: Human, Critical thinking, Sociology, Science, Religion, The Evolution of Cooperation, Reciprocity, Society


Models of cooperation among nonkin suggest that social assortment is important for the evolution of cooperation. Theory predicts that interacting phenotypes, whereby an individual’s behavior depends on the behavior of its social partners, can drive such social assortment. We measured repeated indirect genetic effects (IGEs) during cooperative predator inspection in eight populations of Trinidadian guppies (Poecilia reticulata) that vary in their evolutionary history of predation. Four broad patterns emerged that were dependent on river, predation history, and sex: (i) current partner behavior had the largest effect on focal behavior, with fish from low-predation habitats responding more to their social partners than fish from high-predation habitats; (ii) different focal/partner behavior combinations can generate cooperation; (iii) some high-predation fish exhibited carryover effects across social partners; and (iv) high-predation fish were more risk averse. These results provide the first large-scale comparison of interacting phenotypes during cooperation across wild animal populations, highlighting the potential importance of IGEs in maintaining cooperation. Intriguingly, while focal fish responded strongly to current social partners, carryover effects between social partners suggest generalized reciprocity (in which one helps anyone if helped by someone) may contribute to the evolution of cooperation in some, but not all, populations of guppies.

Concepts: Gene, Genetics, Evolution, Biology, Guppy, Sociology, The Evolution of Cooperation, Reciprocity


The reciprocity norm refers to the expectation that people will help those who helped them. A well-known study revealed that the norm is strong with Christmas cards, with 20% of people reciprocating a Christmas card received from a stranger. I attempted to conceptually replicate and extend this effect. In Study 1, 755 participants received a Christmas card supposedly from a more versus less similar stranger. The reciprocation rate was unexpectedly low (2%), which did not allow for a test of a similarity effect. Two potential reasons for this low rate were examined in Study 2 in which 494 participants reported their likelihood of reciprocating a Christmas card from a stranger as well as their felt suspicions/threat about the card and their frequency of e-mail use. Reciprocation likelihood was negatively correlated with perceived threat/suspicion and e-mail use. It appears that reciprocating a gift from a stranger in offline settings may be less likely than expected.

Concepts: Cognition, Probability density function, Reciprocity, Similarity, Test, Christmas, The Card, Christmas card