Reward can enhance behavioral motivation, elicit positive emotion and optimize the allocation of attention resources for people. Among multiple reward stimuli, monetary and social rewards are typical representative. The development and maturation of brain reward system begins at birth and continues throughout an individual's life. The childhood and adolescence are critical periods for the development of brain reward system. According to previous research, the current study further investigated the developmental changes in reward processes, the incentive differences between monetary and social rewards and how the two kinds of rewards impact the response inhibition behavior for children, adolescents and adults.
In the current study, 8-year-old children and adolescents around 13 years old as well as adults were recruited as experimental participants, Chinese Yuan and smiling faces were regarded as monetary and social rewards. Adapted incentive-delay tasks and self-report questionnaires were adopted to investigate the monetary and social reward processing. Both tasks had three levels of reward magnitudes (no, low and high). In study 1，qualified participants received 15 Chinese Yuan and an honor certificate as monetary and social rewards, respectively. According to the results of studyl，study 2 adopted the technique of ERP to investigate the neural basis of reward processes for children, adolescents and adults. According to the final score of the participants, 9-4_5 Chinese Yuan and honor certificates of five grades were awarded to the participants as monetary and social rewards. Study 3 aimed to investigate the effects of monetary and social rewards on response inhibition behavior. The participants should conduct the classical Simon task at the target responsing stage.The 3 studies drew the following conclusions respectively:
(1)In study 1，the results indicated that both monetary and social reward effectively speeded up responses for all three age groups as reward magnitude increased in the choice reaction time task. Among adolescents and adults, males exhibited faster responses in high reward than low reward condition, while females responded equally fast in both conditions. For children, girls responded faster to high reward than low reward condition. However, boys committed more errors than girls in low and high reward conditions, and they had more errors in high reward than that in no reward condition for social reward. Regarding the subjective ratings, both children and adolescents exhibited higher motivation for social reward than monetary reward.These findings indicated that males in adolescent and adult groups were more sensitive to reward than females, tangible and quantitative social rewards had stronger incentive power than monetary rewards among children and adolescents.
(2) In study2, for the ERP data, cue-P3, target-P2 and target-P3 were investigated to identify the reward motivation, emotional arousal and attention allocation during reward responses. Adults showed larger cue-P3 responses for monetary than social rewards. Adolescents' emotional responses to reward, which were reflected in target-P2, were stronger than those of adults and were effectively regulated by different magnitudes of social reward. Attention allocation (target-P3) was regulated by reward magnitudes more effectively for adolescents than adults, and limited by an immature reward system, attention allocation of children was insensitive to reward magnitudes. The current study revealed that adolescents had heightened sensitivity to reward with inducing stronger emotional arousal and more effective attention allocation during reward processes.
(3) In study 3, cue-P3, target-N2 and target-P3 were investigated to identify the motivation elicition, the regulation effect of monetary and social rewards on conflict monitoring and conflict resolution.The ability of conflict control is ongoing developing during childhood and adolescence. For high reward of social reward female participants responded to the targets slower than male participants and high reward of monetary reward. Different from that of monetary reward, there were no differences on error rate among no, low and high rewards under social reward for female participants. Thereofore, in the tasks which require high accuracy, social reward could be selected to motivate female. Under high reward of monetary reward, incongruent trials elicited more positive frontal-central target-P3 component than congruent trials for adolescents group and girls in the children group. The results indicated that too high behavioral motivation could have negative influence on conflict control behavior.
Above all, monetary and social rewards could motivate individual's behavior effectively. Because of the immature brain reward system, children could not make good use of the reward information to regulate their goal-directed behavior. During childhood, girls are more sensitive to reward than boys. Adolscents are hypersensitive to rewards. Reward could regulate the attention allocation of adolescents effectively. In addition, social reward could regulate adolescents' emotional arousal effectively.For children and adolescents, too high motivation could have negative effect on task-related attention concentration. During adolescence and adulthood, males are more sensitive to reward than female. When measuring an individual's motivation for a reward, objective performance and subjective ratings should be simultaneously considered.