This paper describes the LuminUs - a device that we designed in order to explore how new technologies could influence the inter-personal aspects of co-present musical collaborations. The LuminUs uses eye-tracking headsets and small wireless accelerometers to measure the gaze and body motion of each musician. A small light display then provides visual feedback to each musician, based either on the gaze or the body motion of their co-performer. We carried out an experiment with 15 pairs of music students in order to investigate how the LuminUs would influence their musical interactions. Preliminary results suggest that visual feedback provided by the LuminUs led to significantly increased glancing between the two musicians, whilst motion based feedback appeared to lead to a decrease in body motion for both participants.