When we compare college social science textbooks popular in the 1960's with those used in the 1980's, the first change that strikes us is the proliferation of pictures. The number of pictures has not merely doubled or tripled in twenty years; in many cases pictures have increased exponentially.
Smith, B. D., & Elifson, J. M. (1986). Do Pictures Make a Difference in College Textbooks?. Reading Horizons, 26 (4). Retrieved from http://scholarworks.wmich.edu/reading_horizons/vol26/iss4/10