"One major shift research has called attention to is the dramatic increase in the image-to-word ratio in documents of all kinds (Horn 1998). Many publications that in the past might have used one illustration per article now have one illustration per page. Thus the sheer volume of visual elements has changed. But that is not all. In my characterization of visual language, I focus attention on the tight integration of words and visual elements, whereas in the old document paradigm, words and images are separated. Images were referred to as figures and often did not even appear on the page on which they were discussed. That practice is changing; more and more, words and images are coming together.

Also underway is ìthe Great Sorting Out of the Functions of Words and Images When They Are Tightly Integrated.î In the Sorting Out, we study what words do best and what it is that the visual elements do best when the two are tightly integrated; that is, we are developing the functional semantics of visual language. It turns out that we need a whole set of new guidelines and rules for understanding this tight integration, principles that are quite different from those used when words and images operate separately (Horn 1998). As we understand this integration more and more comprehensively and deeply, we apparently increase the integration of our own words and images. This has happened in my own work on the analysis of the words and images in diagrams: they have become more integrated. The functional semantics of visual language can now be extended to fully effect the tight integration of visual elements and words."

http://www.stanford.edu/~rhorn/a/topic/vl%26id/artclInfoDesignChapter.html