This paper explores the role of materiality in Digital Musical Instruments and questions the influence of tacit understandings of sensor technology. Existing research investigates the use of gesture, physical interaction and subsequent parameter mapping. We suggest that a tacit knowledge of the ‘sensor layer’ brings with it definitions, understandings and expectations that forge and guide our approach to interaction. We argue that the influence of technology starts before a sound is made, and comes from not only intuition of material properties, but also received notions of what technology can and should do. On encountering an instrument with obvious sensors, a potential performer will attempt to predict what the sensors do and what the designer intends for them to do, becoming influenced by a machine centered understanding of interaction and not a solely material centred one. The paper presents an observational study of interaction using non-functional prototype instruments designed to explore fundamental ideas and understandings of instrumental interaction in the digital realm. We will show that this understanding influences both gestural language and ability to characterise an expected sonic/musical response.