EVALUATING 3D TASK-PERFORMANCE FOR FISH TANK VIRTUAL WORLDS

''Fish tank virtual reality'' refers to the use of a standard graphics workstation to achieve real-time display of 3D scenes using stereopsis and dynamic head-coupled perspective. Fish tank VR has a number of advantages over head-mounted immersion VR which makes it more practical for many applications. After discussing the characteristics of fish tank VR, we describe a set of three experiments conducted to study the benefits of fish tank VR over a traditional workstation graphics display. These experiments tested user performance under two conditions: (a) whether or not stereoscopic display was used and (b) whether or not the perspective display was coupled dynamically to the positions of a user's eyes. Subjects using a comparison protocol consistently preferred head coupling without stereo over stereo without head coupling. Error rates in a tree-tracing task similar to one used by Sollenberger and Milgram showed an order of magnitude improvement for head-coupled stereo over a static (nonhead-coupled) display, and the benefits gained by head coupling were more significant than those gained from stereo alone. The final experiment examined two factors that are often associated with human performance in virtual worlds: the lag (or latency) in receiving and processing tracker data and the rate at which frames are updated. For the tree-tracing task, lag had a larger impact on performance than did frame update rate, with lag having a multiplicative effect on response time. We discuss the relevance of these results for the display of complex 3D data and highlight areas requiring further study.