Reid, D. J., & Miller, G. J. A. (1980). Pupils' perception of biological pictures and its implications for readability studies of biology textbooks. Journal of Biological Education, 14(1), 59-69.

It is suggested that the concept of readability should be considered as more than a measure of word complexity. It should take account of the total understanding by readers of printed material. To do this adequately it is necessary to measure the effect that pictures have upon words and vice versa. This study demonstrates that the use of colour, for instance, can be beneficial in the overall understanding of pictures, although it does not have a simple "across the board" effect. Use of colour improves observation, but may sometimes act as a distractor. It also affects the strategems by which children scan pictorial material. One of the reasons why pictures are generally considered to be "a good thing" arises from the common confusion between the role of pictures in communicating meaning to children, and the readiness with which visual content is remembered by children. Enhancing the latter does not necessarily enhance the former.