Operant hoarding: a new paradigm for the study of self-control.

In the first of four experiments, rats were exposed to a modified multiple continuous reinforcement-extinction schedule during 15-min daily sessions. In one condition (saves condition) with the cuelight on, a single lever press produced a food pellet, briefly extinguished the cuelight, and started a clock. Saves (additional lever presses with interresponse times less than 1 s) produced an additional food pellet, briefly extinguished the cuelight, and restarted the interresponse time clock. The cuelight was extinguished 1 s after the last lever press and remained off during a 10-s period of extinction, during which no food pellets were delivered. In the other condition (savings account condition), the contingencies were the same except that the cuelight was extinguished and was not reilluminated after the initial lever press, and the delivery of all food pellets in the reinforcement component was delayed until the onset of extinction. In both conditions, rats made saves, but mean saves (total saves divided by the number of reinforcement components) were slightly reduced in the savings account condition. In Experiment 2, using six equally spaced 15-min sessions per day on alternate days, saves were either followed immediately with food and brief cuelight offset (saves condition) or were not reinforced at all. Mean saves were much greater when saves were reinforced. In Experiment 3, during 5-min daily sessions, saves earned a single pellet (savings account condition) or a number of pellets equal to the ordinal number of the lever press (interest condition). Rats made fewer mean saves, with little change in the food rate, when saves earned interest. In Experiment 4, the rats earned all their food in the operant situation during 24 daily 5-min sessions, these separated by 55-min intersession intervals during which no food was available; otherwise, the conditions were the same as in Experiment 3. In Experiment 4, the shift to interest for saves led to an increase in mean daily mean saves (total daily mean saves divided by the number of daily sessions) as well as to an increase in the number of food pellets delivered in each session. The results are discussed in terms of self-control and behavioral economics.     

Absence of anticipatory contrast in rats trained on multiple schedules.

Rats were trained on three- and four-component multiple schedules in which two of the components were correlated with identical reinforcement schedules that remained unchanged throughout training. These target components differed in terms of whether their respective following schedules were either higher or lower in value. Unlike corresponding experiments previously reported with pigeons, higher response rates occurred in the target component followed by a higher valued schedule than in the target component followed by the lower valued schedule. Overall contrast effects occurred independently of these sequential effects, but were inconsistent across subjects. The results suggest that the effects of a following schedule of reinforcement are opposite for pigeons and rats, and that one reason previous studies have often failed to show contrast effects with rats is that the effects of the following schedule in rats are in competition with contrast dynamics.     

Free birds aren't fat: Weight gain in captured wild pigeons maintained under laboratory conditions

Nine feral pigeons, 5 from an urban setting and 4 from a rural setting, were captured and maintained for 42 days under free-feeding conditions comparable to those arranged for laboratory subjects. On average, birds increased their body weights by 17% over this period. The range of increase across birds was 9 to 30%. These findings suggest that the food deprivation arranged for laboratory pigeons, which is characteristically 80% of free-feeding weights, may in some sense be less severe than it first appears.     

Control over response number by a targeted percentile schedule: reinforcement loss and the acute effects of d-amphetamine.

Two fixed-consecutive-number-like procedures were used to examine effects of acute d-amphetamine administration on control over response number. In both procedures, rats were required to press the left lever at least once and then press the right lever to complete a trial. The consecutive left-lever presses on each trial comprised a "run." Under the targeted percentile schedule, reinforcement was provided if the current run length was closer to the target length (16) than half of the most recent 24 runs. This differentially reinforced run length while holding reinforcement probability constant at .5. A second group acquired the differentiation under the targeted percentile schedule, but were then shifted to a procedure that yoked reinforcement probability by subject and run length to that obtained under the targeted percentile schedule. The two procedures generated practically identical control run lengths, response rates, reinforcement probabilities, and reinforcement rates. Administration of d-amphetamine disrupted percentile responding to a greater degree than yoked control responding. This disruption decreased reinforcement frequency less in the former than the latter procedure. The similar baseline responding under these two procedures suggests that this difference in sensitivity was due to behavioral adjustments to drug prompted by reduction of reinforcement density in the yoked control but not the percentile schedule. These adjustments attenuate the drug's effects under the former, but not the latter, procedure.     

Cocaine and food as reinforcers: effects of reinforcer magnitude and response requirement under second-order fixed-ratio and progressive-ratio schedules.

Reinforcer magnitude and fixed-ratio requirement were varied under two second-order schedules. Under one, the first sequence of a fixed number of responses completed after the lapse of a 10-min fixed interval produced reinforcement. Under the second, a second-order progressive-ratio schedule, the fixed number of responses increased after each reinforcement. Either cocaine (0 to 300 micrograms/kg/inj) or food (0 to 5,700 mg/delivery) reinforcers were delivered. Under some conditions, a 2-s illumination of stimulus lights occurred on completion of each ratio sequence. Under the second-order schedule, as cocaine dose or amount of food increased, rates of responding increased; at the highest values, rates of responding decreased. Increases in the ratio requirement from 10 to 170 responses minimally decreased overall response rates. Under the second-order progressive-ratio schedule, increases in dose of cocaine or amount of food increased rates of responding; at the highest amounts of food, rates of responding decreased but response rates at the highest dose of cocaine remained relatively high. The highest ratio requirement that was completed (breaking point) depended on the dose of cocaine but was less dependent on the amount of food. Removing brief-stimulus presentations had a greater effect on completion of ratio requirements with cocaine compared to food.     

Effects of schedule of reinforcement on a pentobarbital discrimination in rats.

The purpose of this study was to determine the effects of the schedule of reinforcement on a pentobarbital discrimination in rats. Five rats were trained to discriminate 10 mg/kg pentobarbital from saline under a multiple fixed-interval 180-s fixed-ratio 20 schedule of reinforcement. During both saline and pentobarbital training sessions, subjects emitted a higher percentage of correct responses under the fixed-ratio component as compared to the fixed-interval component of the multiple schedule. Determination of the pentobarbital dose-response curve under the fixed-ratio component resulted in a steep curve characterized by responding on the saline lever at low doses and on the drug lever at higher doses. Under the fixed-interval component, a graded dose-effect curve was produced, with considerable responding on both levers after intermediate doses of pentobarbital. The administration of phencyclidine and MK-801 resulted in an intermediate level of drug-lever responding for some subjects. Administration of d-amphetamine resulted in saline (nondrug) appropriate responding. The results of this study demonstrate that the schedule of reinforcement is a determinant of drug stimulus control, just as it is a determinant of other drug effects.     

Compassion-Focused Therapy to Reduce Body Weight Shame for Individuals With Obesity: A Randomized Controlled Trial

Adults living in larger bodies (Body Mass Index > 30) often experience body weight shame, are highly self-critical, and are at increased risk for anxiety and depression. To date, there have been no RCTs examining the efficacy of Compassion-Focused Therapy (CFT) to help those experiencing body weight shame. The aim of the current study was to investigate the efficacy of CFT as a 12-session group intervention to reduce body weight shame for individuals living in larger bodies. The study used an RCT design with participants randomized to the CFT (n = 28) or waitlist control (n = 27) condition. Participants in both groups were assessed at pre- and postintervention, with the CFT group alone assessed at 3- and 6-month follow-up intervention. Both self-report and a physiological measure of parasympathetic nervous system activity were used (i.e., heart rate variability). Results indicated that CFT had a significant positive impact at postintervention compared to the control group for body weight shame (internal and external), increasing self-compassion, reducing fears of compassion (self, other, and receiving), reducing self-criticism, and reducing external shame. Although there were no significant group effects at postintervention on depression and anxiety, 66% of participants had clinical improvement on depression in the CFT group compared to 8% in the control group at postintervention. CFT did not shift baseline heart rate variability at postintervention. The evidence from this RCT supports CFT as an efficacious intervention to reduce body weight shame for individuals with obesity.     

基于预期理论的风险决策的神经机制

预期理论基于对期望效用理论的批判与发展,提出了价值函数与权重函数,对以往风险决策研究中所发现的现象进行了很好的预测与解释。预期理论的核心概念包括参照依赖、损失规避与权重函数。基于预期理论的一些决策偏差包括框架效应、禀赋效应和默认偏差也部分揭示了与人们风险决策有关的脑区。近年来,通过采用功能性核磁共振等脑成像手段对预期理论的一些核心成分进行的研究表明,涉及到人们风险决策的脑区主要有前额叶、纹状体、脑岛与杏仁核。未来的研究可以从预期理论的产生根源、个体发展以及遗传基因等角度进行进一步的探讨。     

Differential effects of approach bias and eating style on unhealthy food consumption in overweight and normal weight women

Objective: The current study aimed to examine the effects of approach bias for unhealthy food and trait eating style on consumption of unhealthy food in overweight and normal weight individuals.

Method: Participants were 245 undergraduate women aged 17 – 26 years. They completed an Approach–Avoidance Task, the Dutch Eating Behaviour Questionnaire (to assess restrained, emotional, and external eating), and a taste test to measure consumption of unhealthy food.

Results: An external eating style predicted increased consumption of unhealthy food. Among overweight participants, external and emotional eating style individually moderated the relationship between approach bias for unhealthy food and subsequent consumption. Specifically, approach bias was positively related to consumption in high external and emotional eaters, but negatively related to consumption in low emotional eaters. These interactions were not observed among normal weight participants.

Conclusion: Practically, the results suggest that overweight individuals who are external or emotional eaters may benefit from interventions that aim to modify approach bias towards unhealthy food cues to reduce problematic eating behaviour.     

Body perception and meal type across age and gender on a Mediterranean island (Sardinia)

Our aim was to describe the differences in consumption of types of meal (complete/incomplete) eaten at lunch and dinner by gender in people of different age groups (children, young adults and seniors). In particular, we wanted to investigate the differences in choice of meal based on perceived weight. The study involved 516 participants, of which 156 were children (8-12y), 187 were young adults (19-30y) and 173 were elderly (65-90y). A cross-sectional analysis was carried out into the choice of meal type based on the different age groups and genders, on the three Body Mass Index categories (under, normal, overweight), on the three levels of self-perception (slim, normal and heavy) and on the degrees of perception of one’s body weight (underestimation, accurate estimation, overestimation). The food eaten was grouped into three types of daily meal: (a) incomplete, (b) complete lunch or dinner, (c) always complete. Differences emerged in the type of meal eaten according to age, gender and perceived weight. The results show gender differences in associations with meal type according to the way in which body mass is measured or perceived. The choice of complete/incomplete meal type changes according to whether real weight or perceived weight is considered.