Elicitation of requirements is a key step of the design activity. The building of a shared understanding of design requirements is essential to the performance of the design. Personas and scenarios are used in order to define end users and their needs. Their usage is becoming more and more popular, especially in Software and System Engineering and Human Computer Interaction (HCI). Our hypothesis is that scenarios and personas improve shared understanding of functional re- quirements between co-designers. In order to test this hypothesis, an empirical study has been undertaken in a laboratory context. This paper presents the proto- col of the study and discusses the indicators used for measurement of shared un- derstanding.