This study examined the amounts of information that students represented in diagrams compared to text when taking notes (self-directed communication) and when constructing explanations for others (others-directed communication). The participants were 98 Japanese university students who read one of two passages (differing in imageability) in Japanese (L1) and in English (L2). While reading, they could take notes, and were subsequently requested to produce an explanation of the passage using L1 or L2. The students represented more information in diagrams in notes they took from the passage of higher imageability in L1. However, in their explanation of that same passage for others - still using L1 - they represented more information in text. This finding suggests perceptual differences about the functions of diagrams in self- and others-directed communication. Results also confirmed that passage imageability and students' language proficiency affect cognitive processing cost, which in turn influences the extent to which diagrams are used.