Our brains interpret visual signals in specific, predictable ways, and modern user interfaces and consumer products are based on extensive study in this area. The way we interact with visual signals was first formally studied and discussed by William Cleveland and Robert McGill (at the time, with AT&T Laboratories) in their seminal paper named Graphical Perception: Theory, Experimentation, and Application to the Development of Graphical Methods, as published in the Journal of the American Statistical Association in September 1984. This paper is readily available via a quick Internet search, and it is worth a quick read.

In addition to Cleveland and McGill, who were statistical scientists (and later professors) focused on researching how we process visual cues, Stephen Few has written extensively on this topic in his books and on his blog, which can be viewed by visiting http://www.perceptualedge.com/.

The authorities on this matter have concluded that the...