Users evaluating physical, virtual, and mixed reality prototypes exhibit differential DLPFC brain activity

The emergent use of mixed reality (MR) technology in product development and evaluation provides new opportunities for prototyping across the physical and virtual domain. However, it is unknown how MR prototypes affect users' cognitive processes during final stage product evaluation. This experiment explores how different prototype representations-physical, virtual, and MR-affect users' DLPFC brain activity as measured by functional near-infrared spectroscopy (fNIRS), subjective workload, and affective state. N_total=88 participants split in three independent groups received either a physical (N = 30), virtual (N = 30), or MR (N = 28) representation of a power drill, tasked to evaluate its usability and propose a design change. The results demonstrate significantly different oxygenated and deoxygenated haemoglobin concentration changes in users' dorsolateral prefrontal cortex (DLPFC), depending on representation mode (i.e., physically, virtual, or MR), and task (i.e., evaluation or proposing a design change). While there were some between-group differences in physical demand and subjective performance, other subjective workload and affective state measures did not significantly differ. These results are novel, demonstrating that users' DLPFC brain activity differ depending on prototype representation mode. This could imply differing cognitive processes, but further research is required. Nevertheless, choosing prototype representation mode is not trivial and should be a careful consideration.