Joseph L. Gabbard and Deborah Hix.
 <b>A Taxonomy of Usability Characteristics in Virtual
  Environments</b>.
 Technical report, Virginia Polytechnic Institute and State
  University, Blacksburg, Virginia, November 1997.
  <a href="http://vis.cs.brown.edu/docs/pdf/bib/g/Gabbard-1997-TUC.pdf.html">(pdf)</a>
  <a href="http://vis.cs.brown.edu/results/bibtex/Gabbard-1997-TUC.bib">(bibtex:
  Gabbard-1997-TUC)</a>.