 On a more practical theme, AI researchers, one of whose main concerns is the heuristic power of representation systems in addition to their expressive power, have been debating about different forms of representation for decades (Sloman  1971,  1985,  1995).  Hence, they have welcomed discussions of the distinct role of visual reasoning and have recently hosted interdisciplinary symposiums on diagrammatic reasoning at AI  conferences.[11]  At the same time, realizing that human beings adopt different representation forms depending on the kinds of problems they face, some AI researchers and design theorists have practiced domain-specific approaches to bringing in problem-tailored representation  forms.[12]