We introduce and present preliminary results for a hybrid display system combining head-mounted and projector-based displays. Our work is motivated by a surgical training application where it is necessary to simultaneously provide both a highfidelity view of a central close-up task (the surgery) and visual awareness of objects and events in the surrounding environment. In this article, we motivate the use of a hybrid display system, discuss previous work, describe a prototype along with methods for geometric calibration, and present results from a controlled human subject experiment. This article is an invited resubmission of work presented at IEEE Virtual Reality 2003. The article has been updated and expanded to include (among other things) additional related work and more details about the calibration process.

We compare two technological approaches to augmented reality for 3-D medical visualization: optical and video see-through devices. We provide a context to discuss the technology by reviewing several medical applications of augmented-reality re search efforts driven by real needs in the medical field, both in the United States and in Europe. We then discuss the issues for each approach, optical versus video, from both a technology and human-factor point of view. Finally, we point to potentially promising future developments of such devices including eye tracking and multifocus planes capabilities, as well as hybrid optical/video technology.