The focus of this paper is a comparison comparison of two existing approaches to the evaluation of usability of virtual environments (VEs): testbed evaluation and sequential evaluation. Bowman is one of the authors of the testbed evaluation (1999), while Gabbard and Hix are authors of the sequential evaluation (1999). The most interesting aspect of the paper is the discussion on how the result obtained with one approach can be used to improve the other.

The methods are discussed and compared on the basis of the problems, which underlie the evaluation of VEs. In particular, the difficulties in relying on traditional usability methods for use in interfaces are illustrated in light of differences in the physical environment, the role of evaluators, the user population, and the type of evaluation. Existing usability methods for VEs are reviewed, and an interesting classification is proposed according to three features: involvement of representative users, context of evaluation, and types of results produced. Testbed and sequential evaluations are compared, taking into account this classification.

Software engineers and people working in the field of human-computer interaction will be interested in this topic. The presentation of the paper is quite clear and well organized. However, practical applications of the comparison of the two methods are not presented, thus limiting the interest of the paper.