Rejection of unfair offers in the ultimatum game is no evidence of strong 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.     

Association Between Glucan Synthesis by Streptococcus mutans and Caries Incidence in Schoolchildren Receiving a Fluoride Mouth Rinse

Purpose: To determine whether variation in glucan synthesis by Streptococcus mutans isolates is associated with caries development in children receiving a fluoride mouth rinse (FMR). Materials and Methods: Of 122 children (aged 9 to 10 years), 64 had received FMR (FMR(+) group) and the remaining 58 children had not (FMR(-) group). The number of decayed and filled teeth (DFT) and increases in the number of DFT in 1 year (dDFT) were recorded. Saliva samples were collected to isolate the clinical S. mutans strains. The isolates were incubated in heart infusion broth supplemented with 1% sucrose, then the amount of water-insoluble glucan (WIG) formed on a glass tube surface was evaluated. Results: In the FMR(-) group, children carrying S. mutans had a higher DFT (P = 0.039) and tended to have a higher dDFT (P = 0.080) than the others. In the FMR(+) group, although the differences between children with and without S. mutans were not significant, children carrying S. mutans that produced a high amount of WIG had higher dDFT than the other S. mutans-positive children (P = 0.034). Conclusions: This study revealed that the variation in glucan synthesis by S. mutans is associated with caries development in children receiving a FMR.     

Autofluorescence imaging and the quantitative intensity of fluorescence for evaluating the dysplastic grade of colonic neoplasms

Background and aims

Autofluorescence imaging (AFI) is a novel technology which can capture fluorescence emitted from intestinal tissues. While AFI is useful for detecting colorectal neoplasms, it is unclear whether AFI can facilitate the diagnosis by differentiating the extent of dysplasia of colorectal neoplasms. This study investigated the efficacy of AFI in discriminating high-grade from low-grade adenoma.

Materials and methods

Sixty-seven patients who underwent colonoscopy with AFI were enrolled in this study. The AFI images obtained from 158 lesions in these patients were visually classified into four categories, namely, green (G), green with magenta spots (GM), magenta with green spots (MG), and magenta (M), according to their color intensities, immediately after the examination. The AFI images of the lesions were quantified using an image-analytical software program (F index). Either the F index or the visual assessment was prospectively compared with the dysplastic grade.

Results

The F index of the high-grade adenomas was significantly lower than that of the low-grade adenomas, hyperplasia, and normal mucosa (p?Conclusions AFI, particularly the F index, is considered to be a useful procedure for estimating the dysplastic grade of colonic adenomas.