Future altruism: Social discounting of delayed rewards

Social discounting assesses an individual's willingness to forgo an outcome for the self in lieu of a larger outcome for someone else. The purpose of the present research was to examine the effect of adding a common delay to outcomes in a binary choice, social discounting procedure. Based on the premise that both social and temporal distances are dimensions of psychological distance, we hypothesized that social discounting should decrease as a function of delay to the outcomes. Across two within-subject experiments, participants indicated preference between a hypothetical money reward for the self or for someone else. The outcomes were associated with no, short, and long delays. Both studies confirmed our hypothesis that adding any delay to the receipt of outcomes decreases social discounting, though no significant differences were observed between short and long delays. These results are discussed in the context of some existing literature on altruism.     

Within-subject differences in degree of delay discounting as a function of order of presentation of hypothetical cash rewards

Procedural variants in estimating delay discounting (DD) have been shown to yield significant differences in estimated degree of DD as well as variations in individual patterns of choice. For example, a recent study found significantly different degrees of DD between groups assessed using either an ascending or descending order of presentation of the immediately available rewards. The purpose of this study was to test for within-subject effects of order of presentation of the immediate rewards in a DD task. In a single session, college students (N = 29) were asked to complete two DD tasks, one with the immediate rewards presented in ascending order and one in descending order. Consistent with previous results, significantly larger mean area under the discounting curve (AUC) was observed when the descending sequence was used compared to the ascending order of presentation; and the correlation between both measurements was moderate. These results suggest that some DD assessment tasks may be sensitive to contextual variables such as order and range of the reward and delay values.     

Probability and delay discounting of hypothetical sexual outcomes

The present study used the discounting procedure to characterize choice behaviors regarding hypothetical sexual outcomes. Eighty-six adult undergraduate students completed computerized delay and probability discounting tasks concerning hypothetical money and hypothetical sexual activity. Consistent with other discounting findings, hyperbolic and hyperbola-like decay models described individual and group median indifference point data well. These findings contribute to a growing literature on the relevance of the discounting procedure to decision-making processes and suggest that the discounting procedure may be useful for understanding the processes that underlie social problem behaviors associated with impulsive sexual decisions.     

Delay of gratification and delay discounting in rats

Delay discounting (DD) and delay of gratification (DG) are two measures of impulsive behavior often viewed as reflecting the same or equivalent processes. However, there are some key differences in the contingencies of reinforcement between the procedures that may have implications for understanding impulsivity. This study used DD and DG procedures to determine if differences in contingencies of reinforcement specified by DD and DG alters how much organisms discount the value of delayed reinforcers. Twenty-four water-deprived rats performed one of two Adjusting Amount procedures, which consisted of repeated choices between a fixed amount of water (250 &mgr;l) delivered after a delay (0, 4, 8, 16, or 32 s) and an adjusting, usually lesser amount delivered immediately. Half of the rats (n=12) performed a DD procedure designed to assess preference for immediate over delayed reinforcers in which they had discrete choices between the immediate and delayed amounts of water. A DG procedure was used for the other half of the rats (n=12). In the DG procedure rats also selected between immediate and delayed alternatives, but if they chose the delayed alternative they could switch to and receive the immediate alternative at any time during the delay to the larger reward. In the DD procedure switching responses were not reinforced but were still recorded and used for analyses. The DD functions of the two groups did not differ significantly. However, at the longer delays, the DG group made significantly fewer switching responses than the DD group. A possible role of response inhibition in the DG procedure is discussed.     

Parameters of delay discounting assessment: number of trials, effort, and sequential effects.

Procedural variants in estimating delay discounting (DD) have been shown to yield significant within-subject differences in estimated degree of delay discounting as well as variations in the patterns of choice. The purpose of this study was to evaluate the effect of subject control over the number of trials in a delay discounting task, on degree of delay discounting. Participants were assessed with two computerized DD assessments: the full-length method presented participants with a fixed set of 240 trials, and the abbreviated task, where once participants had shown indifference between the immediate and delayed rewards, the remaining trials for that delay value were omitted. While the full-length and abbreviated methods did not differentially affect patterns of choice or estimated delay discounting, the order of presentation (ascending or descending) of immediate rewards produced differences in each measure: rate of delay discounting was significantly lower when estimated with the descending sequence; a larger proportion of area under the discounting curve was concentrated around the indifference point trial with the descending sequence; and a lower correlation was observed between estimates obtained across methods with the descending sequence.     

Domain independence and stability in young and older adults' discounting of delayed rewards

Individual discounting rates for different types of delayed reward are typically assumed to reflect a single, underlying trait of impulsivity. Recently, we showed that discounting rates are orders of magnitude steeper for directly consumable liquid rewards than for monetary rewards (Jimura et al., 2009), raising the question of whether discounting rates for different types of reward covary at the individual level. Accordingly, the present study examined the relation between discounting of hypothetical money and real liquid rewards in young adults (Experiment 1) and older adults (Experiment 2). At the group level, young adults discounted monetary rewards more steeply than the older adults, but there was no significant age difference with respect to liquid rewards. At the individual level, the rates at which young and older participants discounted each reward type were stable over a two- to fifteen-week interval (rs > 70), but there was no significant correlation between the rates at which they discounted the two reward types. These results suggest that although similar decision-making processes may underlie the discounting of different types of rewards, the rates at which individuals discount money and directly consumable rewards may reflect separate, stable traits, rather than a single trait of impulsivity.     

Delay and probability discounting as related to different stages of adolescent smoking and non-smoking

This study examined relations between different patterns of adolescent cigarette smoking and discounting of monetary rewards due to delay (delay discounting) and probabilistic uncertainty (probability discounting). The study also examined the relation between smoking and the number of peer friends who smoke and level of parent education. Participants were 55 adolescents (28 females) between 14 and 16 years of age who were categorized according to the following patterns of smoking behavior: "never smokers" (n=19; 10 females) who had not tried even one cigarette; "triers" (n=17; 9 females) who had recently tried cigarettes for the first time; and "current smokers" (n=19; 9 females) who smoked a minimum of one cigarette every week for at least 6 months prior to data collection. It was hypothesized that current smokers would discount more than those who had never smoked. No specific hypotheses were made for participants only trying cigarettes. Unexpectedly, results indicated no differences in discounting between the current smokers and never smokers. However, the trier group discounted probabilistic rewards significantly more than the never- and current-smoker groups. Also, triers and current smokers both reported having more friends who smoked than never smokers, and fathers of never smokers had significantly more education than fathers of either triers or current smokers. These results suggest that impulsive discounting may be more related to adolescents trying cigarettes than to their becoming regular smokers, whereas number of peer friends who smoke and parent level of education seem to differentiate between those who have smoked to some extent (triers and current smokers) and those who have not even tried cigarettes (never smokers).     

n种群Lotka-Volterra时滞系统的全局稳定性，Ⅲ:必要性

本文考虑无对角时滞的ｎ种群Ｌｏｔｋａ－Ｖｏｌｔｅｒｒａ时滞系统，证明了弱对角占优（ＷＤＤ）为系统关于所有时滞全局稳定的充要条件。     

Time discounting,present biases,and health-related behaviors: Evidence from Japan

Human health is considered the outcome of intertemporal choices under tradeoffs between a small immediate reward and a larger delayed reward. Health-related behaviors are thus affected by personal time preferences. Based on an Internet-based survey conducted on Japanese adults, we contribute to the literature by incorporating the multifaceted nature of time discounting in an analysis of the associations between time preference and health-related behaviors. We find that, first, less patient respondents tend to exhibit worse health-related attributes. Second, present bias, which is measured by the degree of declining impatience, is positively associated with unhealthy behaviors for naïve respondents, who are unaware of their self-control problem. Third, such associations cannot be found in sophisticates, who are aware of that. As a policy implication, direct intervention policies, including “nudging,” are more effective than a commitment device provision in correcting the unhealthy behaviors due to present bias. Fourth, the sign effect, wherein future losses are discounted at a lower rate than future gains, is negatively associated with unhealthy outcomes, although at weak statistical significance levels.     

Squalene synthase: steady-state, pre-steady-state, and isotope-trapping studies

Squalene synthase catalyzes two consecutive reactions in sterol biosynthesis-the condensation of two molecules of farnesyl diphosphate (FPP) to form the cyclopropylcarbinyl intermediate presqualene diphosphate (PSPP) and the subsequent rearrangement and reduction of PSPP to form squalene. Steady-state and pre-steady-state kinetic studies, in combination with isotope-trapping experiments of enzyme.substrate complexes, indicate that two molecules of FPP add to the enzyme before NADPH and that PSPP is converted directly to squalene without dissociating from the enzyme under normal catalytic conditions. In addition, formation of PSPP or a prior conformational change in squalene synthase is the rate-limiting step for synthesis of squalene from FPP via PSPP in the presence of NADPH and for synthesis of PSPP in the absence of NADPH. Squalene synthase is inhibited at high concentrations of FPP. Inhibition is specific for the formation of squalene, but not PSPP, and is competitive with respect to NADPH. In addition, the binding of either NADPH or a third, nonreacting molecule of FPP stimulates the rate of PSPP formation. A kinetic mechanism is proposed to account for these observations.     

Discrimination,discounting and impulsivity: a role for an informational constraint

Feeding animals often prefer small, quickly delivered rewards over larger, more delayed rewards. Students of feeding behaviour typically explain this behaviour by saying that animals discount delayed benefits. Temporal discounting implies that delayed benefits are worth less than immediate benefits. This paper presents a new explanation of short-sighted decision-making called the discrimination advantage model that does not rely on discounting. A new model that includes several possible causes of discounting is developed. This model has many interesting features, but it cannot account for two empirical results: the strength of the 'discounting' effect and the fact that the time between choice presentations (the intertrial interval or ITI) has no effect. This leads to the conclusion that although discounting may be important it is probably not a complete explanation of the experimental facts. In the discrimination advantage model the observation that the ITI does not affect choice is seen as a strategy to make a cleaner discrimination between delayed alternatives in a noisy world. A simple example shows that when discrimination is imperfect a short-sighted choice rule can, in some situations, lead to a higher long-term rate than a rule that actually compares long-term rates. This idea is developed and extended in several ways.     

Discounting of delayed hypothetical money, alcohol, and food

For drug-dependent individuals, drugs of abuse that are delayed in time are discounted more steeply than money delayed in time in a hypothetical choice task. The reasons for this finding are not clear. This study examined whether steep discounting of drugs relative to money might be related to the function of drugs as primary/consumable reinforcers and money as a conditioned/non-consumable reinforcer. Twenty adults with no self-reported problems with money, alcohol, or food participated. They indicated their preferences for three hypothetical outcome types: delayed versus immediate money, delayed versus immediate food, and delayed versus immediate alcohol. Both the hyperbolic decay model and area under the curve analysis showed that money was discounted less steeply than alcohol or food, but that alcohol and food were discounted similarly. This finding replicates previous results showing that people without drug abuse problems show steep discounting of alcohol. Furthermore, this finding suggests that alcohol may be steeply discounted as part of a general process involving primary/consumable reinforcers, not necessarily because it is a drug.     

Conflict, sticks and carrots: war increases prosocial punishments and rewards

Unlike most species, humans cooperate extensively with group members who are not closely related to them, a pattern sustained in part by punishing non-cooperators and rewarding cooperators. Because internally cooperative groups prevail over less cooperative rival groups, it is thought that violent intergroup conflict played a key role in the evolution of human cooperation. Consequently, it is plausible that propensities to punish and reward will be elevated during intergroup conflict. Using experiments conducted before, during and after the 2006 Israel-Hezbollah war, we show that, during wartime, people are more willing to pay costs to punish non-cooperative group members and reward cooperative group members. Rather than simply increasing within-group solidarity, violent intergroup conflict thus elicits behaviours that, writ large, enhance cooperation within the group, thereby making victory more likely.     

A steady-state study on the formation of Compounds II and III of myeloperoxidase

The reaction between native myeloperoxidase and hydrogen peroxide, yielding Compound II, was investigated using the stopped-flow technique. The pH dependence of the apparent second-order rate constant showed the existence of a protonatable group on the enzyme with a pKa of 4.9. This group is ascribed to the distal histidine imidazole, which must be deprotonated to enable the reaction of Compound I with hydrogen peroxidase to take place. The rate constant for the formation of Compound II by hydrogen peroxide was 3.5.10(4) M-1.s-1. During the reaction of myeloperoxidase with H2O2, rapid reduction of added cytochrome c was observed. This reduction was inhibitable by superoxide dismutase, and this demonstrates that superoxide anion radicals are generated. When potassium ferrocyanide was used as an electron donor to generate Compound II from Compound I, the pH dependence of the apparent second-order rate constant indicated involvement of a group with a pKa of 4.5. However, with ferrocyanide as an electron donor, protonation of the group was necessary to enable the reaction to take place. The rate constant for the generation of Compound II by ferrocyanide was 1.6.10(7) M-1.s-1. We also investigated the reaction of Compound II with hydrogen peroxide, yielding Compound III. Formation of Compound III (k = 50 M-1.s-1) proceeded via two different pathways, one of which was inhibitable by tetranitromethane. We further investigated the stability of Compound II and Compound III as a function of pH, ionic strength and enzyme concentration. The half-life values of both Compound II and Compound III were independent of the enzyme concentration and ionic strength. The half-life value of Compound III was pH-dependent, showing a decreasing stability with increasing pH, whereas the stability of Compound II was independent of pH over the range 3-11.