Greame S. Halford, Rosemary Baker, Julie E. McCredden, and John D. Bain.
  <b>How Many Variables Can Humans Process?</b>
  <i>Psychological Science</i>, 16(1):70-76, 2005.
  <A HREF="http://vis.cs.brown.edu/docs/pdf/bib/g/Halford-2005-HMV.pdf.html">(pdf)</A>
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Halford-2005-HMV.bib">(bibtex:
  Halford-2005-HMV)</A>.<br />