The "Vision Thing"
http://www.pantos.org/atw/35396.html

Sullivan, Terry
All Things Web
1996

Abstract:

It's important for Web designers to have a basic understanding of the mechanics of human visual perception. To the extent that your pages are 'easy on the eyes,' readers will find your site more inviting and more readable. Conversely, pages that visually overstimulate a reader are not only more difficult to read, but much more likely to result in eyestrain, fatigue, even headaches (none of which is particularly popular among readers).