Altruistic Decisions

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.

Both behavioral task (audience effect and vicarious reward) will be studied in fMRI (functional Magnetic Resonance Imagery). The same paradigms used in the behavioral experiment will be adapted for fMRI. Audience Effect experiment: trials will last for 10 seconds maximum. With 80 trials for each condition (public easy, public difficult, private easy and private difficult), the task will count a total of 320 trials and have a 54 minutes duration, in 3 runs of 17 minutes each. Vicarious Reward experiment: trials will have a 10 seconds maximum duration. Using 40 trials for each condition (other low payoff, other high payoff, self low payoff, self high payoff, control condition), the task will have a total of 200 trials and last for 54 minutes, in 6 runs of 9 minutes each.

Both behavioral task (audience effect and vicarious reward) will be studied in MEG (MagnetoEncephaloGraphy). The same paradigms used in the behavioral experiment will be used in MEG. Audience Effect experiment: trials will last for 7 seconds maximum. With 100 trials for each condition (public easy, public difficult, private easy and private difficult), the task will count a total of 400 trials and have a 47 minutes duration. Every 100 trials (about 12 minutes of tasks), a break will be proposed to the participants. Vicarious Reward experiment: trials will have a 7.2 seconds maximum duration. Using 75 trials for each condition (other low payoff, other high payoff, self low payoff, self high payoff, control condition), the task will have a total of 375 trials and last for 45 minutes. Every 125 trials (every 15 minutes), a break will be proposed to the participants.