This study aimed at measuring objectively the experience of using social network sites (SNSs). At this aim, a model of experience has been defined, focusing on three main aspects of time-space continuum of individuals' states: physiological arousal, emotional valence, and attentional resources. At this purpose we developed a new approach to assess such an experience. The main idea is to consider arousal, valence and attention to track the users' experience collecting psychophysiological indexes at predefined period (for example each 10 seconds) to build an empirical model based on these data. Once we got the empirical curve we can fit these data using mathematical models.