Towards a Framework for Design and Evaluation of Mixed Initiative Systems: Considering Movement as a Modality Cristian Bogdan 1 and Michael G¨ oller 2 1 Royal Institute of Technology (KTH), Stockholm, Sweden, cristi@csc.kth.se 2 Research Center for Information Technology (FZI), Karlsruhe, Germany, goeller@fzi.de Abstract. We propose a framework for design and evaluation of mixed initiative robotic systems, focusing mostly on the robot initiative in the case of a robotic shopping trolley. Throughout, we consider the implica- tions of the movement modality in the robot initiative and the commu- nication that follows it. We illustrate our considerations with our experi- ence in designing and evaluating mixed-initiative human-robot communi- cation with a mock-up robot and subsequently an actual robot platform. 1 Introduction Constructing robots that propose own initiatives in a socially acceptable manner is a challenging task. Multiple modalities can be used artfully to allow the robot to indicate its initiative in ways that do not disturb the user, yet manage to get the message across. In this position paper we examine the design space for mixed initiative, in the case of a robotic shopping trolley that we are building in the Commrob project (www.commrob.eu), which aims at developing techniques for multimodal communication with robots and the safe navigation in crowded human every-day environments. Furthermore we exemplify within our design space points of interest related to a specific modality, the robot movement, in what is termed “movement as communication” [3]. Multi-modal, mixed initiative interaction is used by our robotic trolley to help the customer to find the desired products without extensive search in big supermarkets and to relieve the customer from the burden to push the shopping cart from his own force all the time, especially if the trolley is heavily loaded or the customer is an elderly person. The interactive Behavior Operated Trolley (InBOT, [2]) is used as development platform and demonstrator Our design space conceptualization proposes the focus of design to support robot initiative around the chronological phases of the human-robot communica- tion: the robot initiative, the human perception of initiative, the human reaction, the robot detection of that reaction, and the robot response to the human reac- tion. With our focus on movement as a modality, we will use as running examples two applications of robot initiatives in the shopping case: