A distinction is possible between what is commonly called experience at first hand and experience at second hand. In the former one becomes aware of something. In the latter one is made aware of something. The process by which an individual becomes aware of something is called perception, and psychological investigators have been concerned with it for generations. The process by which an individual is made aware of something, however, is a stage higher in complexity, and this has scarcely been touched upon by modern experimental psychology. It involves the action of another individual besides the perceiver. Although a precise terminology is lacking for this two-stage process, it is readily described in ordinary language: we speak of being informed, being told, being taught, being shown, or being given to understand. The principal vehicle for this kind of indirect perception is, of course, language. There is another vehicle for obtaining experience at second hand, however, and this is by way of pictures or models. Although much has been written about language, there is no coherent theory of pictures. The attempt to analyse how a picture conveys information is a necessary but highly ambitious undertaking. The following essay cannot claim to do anything but set up working hypotheses for an important field of investigation. 1