Randy Pausch, Dennis Proffitt, and George Williams.
 <b>Quantifying immersion in virtual reality</b>.
 In <em>Proceedings of the 24th annual conference on Computer
  graphics and interactive techniques</em>, pages 13--18. ACM Press/Addison-Wesley
  Publishing Co., 1997.
  <a href="http://vis.cs.brown.edu/docs/pdf/bib/g/Pausch-1997-QIV.pdf.html">(pdf)</a>
  <a href="http://vis.cs.brown.edu/results/bibtex/Pausch-1997-QIV.bib">(bibtex:
  Pausch-1997-QIV)</a>.