Mixed prototyping, combining virtual and physical prototypes, is an emerging method used to aid in usability testing. This study aims to determine when to use a mixed prototype and how to choose its fidelity to validate the usability testing results and reduce the prototyping cost. A 2×2 between-subject experiment was designed to investigate the effects of the media (head-mounted display versus computer monitor) and physical interaction (using a tangible mock-up or not) on the usability evaluation results and other subjective measures. The experiment results showed that, when aesthetic and functional features are controlled, the non-functional mock-up facilitates users in finding problems regarding physical interaction and ergonomics. Media with high immersion positively influenced the users' subjective ratings. Based on the findings of this study, guidelines on how to choose the fidelity of the prototype during different stages of a usability test are suggested to help product developers find a cost-efficient way to conduct usability tests.
Keywords: Ergonomics; Fidelity; Mixed prototype; Usability test.
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