Levie, W. H. (1978). A prospectus for instructional research on visual literacy. Educational Communication & Technology Journal, 26(1), 25-36.

«In summary, it has been suggested that instructional research in visual literacy focus on the study of the symbolic codes of pictorial media. The key question for researchers is: What pictorial cues serve to evoke what mental operations? Or, put differentyly: What mental operations can be represented pictorially?» (p. 35)