Experimental background

The first experimental test of self-recognition in animals was conducted on a group of preadolescent chimpanzees and several species of monkeys (Gallup, 1970). Initially all of the animals acted as if they were seeing other animals when they looked at themselves in the mirror. After a couple of days, however, the chimpanzees (but not the monkeys) began to respond as if they had come to appreciate the dualism implicit in mirrors and now realized that their behavior was the source of the behavior being depicted in the reflection. That is, rather than responding to the mirror as such with species-typical patterns of social behavior, they began to show self-directed responding by using the mirror to respond to themselves (e.g., to investigate parts of their bodies that they had not seen before). In an attempt to validate my impressions of what had transpired, I devised a more rigorous, unobtrusive test of selfrecognition. After the 10th day of mirror exposure the chimpanzees were placed under anesthesia and removed from their cage. While the animals were unconscious, I applied a bright red, odorless, alcohol-soluble dye (rhodamine-B base) to the uppermost portion of an eyebrow ridge and the top half of the opposite ear. The subjects were then returned to their cages in the absence of the mirror and allowed to recover from anesthetization.