There is http://www.typophile.com/node/10246 aside.

See also the bouma of space craft thread, in which I made some spectral plots of different spacing choices for my Century Catalogue.

For additional sources on this topic you may want to have a look at Pelli’s and Legge’s works, both of which offer most of their papers as PDFs:

http://www.psych.nyu.edu/pelli/papers.html and
http://vision.psych.umn.edu/~legge/psychread2.htm

I also found these very interesting:

Anstis, SM, “Size Adaptation to Visual Texture and Print: Evidence for Spatial-Frequency Analysis”, The American Journal of Psychology Vol. 87, No. 1/2, 1974, pp. 261-267

Morris, RA, “Image Processing Aspects of Type”, EP88 Conference on Electronic Publishing, 1988

I discuss Fourier transforms in my UQAM presentation Gestural Exercises, Excursions into the Visual Cortex, and Design. Downloadable links to my slides and script are at:

http://typophile.com/node/32108

My interest in Fourier transforms stemmed from Raph’s plots.