This study has been prepared with a view to the needs of those who design materials for teaching. Working in schools that operate in a social milieu which is dependent on the spoken rather than the written word, and attempting to communicate with non literate adults both school teachers and adult educators urgently need illustrations and visual materials of all kinds. Over the last two decades as teachers and field workers have become aware of the fact that the pictures and diagrams they were using failed as communication channels, so have the research workers followed in their wake, trying to determine the factors that affect the way visual statements are interpreted.