If a decision influences the well-being of another (through monetary payoff), the decision making processes should differ from a decision that would influences only oneself. The difference will be reflected in the reaction-times and in the accuracy of the response to the task. The drift diffusion models care then used to estimate le decision parameter in each condition and understand which parameter is influenced by the beneficiary of the payoff associated with a decision.

Once the decision parameter characterized with behavioral experiment, the study aims to better understand the neural network sustaining the influence of others on the decision making process, by assessing the neural activity related to the decision making processes. Also, the research compares how the brain responses for payoff for others and payoffs for oneself, specially to confirm that these responses are located in different areas of the Anterior cingulate Cortex.

In order to clarify the complex changes in the decision-making processes induced by simple observation by others (audience) , the experiment have two levels of difficulty . These levels of difficulty will be determined in such a way as to achieve better 'public' performance than 'private' when the task is easy (high level of consistency) and poor performance when the task is difficult (low level of coherence) As described in the literature in psychology. Drift diffusion models will be used to better understand the variations in performance, to decipher between a modulation of the diffusion velocity and or of the decision threshold. This study will help characterize how observation by others modulates performance. Once the decision parameter characterized with behavioral experiment, the study aims to better understand the neural network sustaining the impact of observation by others on the decision making process.

Random-dots tasks: dots appear and move, most have a random trajectory but a given proportion of them move coherently to the same direction.

• Vicarious reward Each trial begins with a cue, showing 'me' or 'him' and filled rectangle filled proportionally to the payoff. The cue and the square are depicted in yellow (oneself) or blue (other), depending on the beneficiary. The moving dots are then presented and the subjects respond. At the end of dots motion, the feedback is presented. If the response was correct, a pile of coins proportional to the payoff is shown. For incorrect responses and misses, a red-colored cross is displayed.
• Audience effect Each trial begins with the display of two eyes (public) or a padlock (private). The moving dots are shown and the participant answers. Audience condition changes the information available on accuracy when submitting comments. In the observed condition, an arrow shows the response. In the observed condition, no feedback is displayed.

behavioral data (reaction-times and accuracy) are collected and the decision parameter can be estimated from them using Drift Diffusion Models

behavioral data (reaction-times and accuracy) are collected and the decision parameter can be estimated from them using Drift Diffusion Models

study of the time-locked brain activity

study of the oscillatory activity elicited in the brain