In this paper we present an ambient persuasive system designed to promote balanced participation during group brainstorming. The system gets in-formation from participants’ attention behavior during a brainstorming session and provides visual messages for facilitating balanced participation. In the present study, we investigated the effect that using subtle visual animations and explaining to the users the meaning of the subtle message had on influencing group behavior. Objective measures from data acquired through depth sensors, and subjective responses to questionnaires on usefulness and perceived influence of the technology intervention were collected. The results suggest that the ambient system is better accepted when the persuasive message is expressed in a subtle manner and an explanation of the system’s persuasive strategy is provided.