  Systematic study of self-consciousness and theory of mind in nonhuman animals has roots in an approach to the study of self-consciousness pioneered by Gallup (1970).  Gallup's rationale for linking mirror-self recognition to self-awareness has already been discussed above.  The idea for the experiment came from observations well-known to comparative psychologists that chimpanzees would, after a period of adjustment, use mirrors to inspect their own images.  Gallup used these observations to develop a widely-replicated protocol that appears to allow a scientific determination of whether it is merely the mirror image per se that is the object of interest to the animal inspecting it, or whether it is the image qua proxy for the animal itself that is the object of interest. Taking chimpanzees who had extensive prior familiarity with mirrors, Gallup anesthetized his subjects and marked their foreheads with a distinctive dye, or, in a control group, anesthetized them only. Upon waking, marked animals who were allowed to see themselves in a mirror touched their own foreheads in the region of the mark significantly more frequently than controls who were either unmarked or not allowed to look into a mirror.