Mirror self-recognition (MSR) is a phenomenon with a more than 20–year empirical history that continues to stir controversy and debate (see Parker, Mitchell, & Boccia, 1994b; Swartz & Evans, 1997). Since Gallup's (1970) first description of MSR, the challenge to comparative psychology has been to interpret the phenomenon (see Gallup, 1970, 1977, 1982, 1994; Anderson, 1984; Parker, 1991; Mitchell, 1993a,b, 1994, 1997a,b; Parker & Mitchell, 1994; Swartz, 1997; Swartz & Evans, 1997). Gallup's subjects were four common chimpanzees (Pan troglodytes), aged approximately 3.5 to 6 years (Swartz & Evans, 1994, 1997). The phenomenon, as described by Gallup (1970), is as follows.
Chimpanzees were provided with visual access to a mirror 8 hours a day for 10 days. The subjects were caged singly for the duration of mirror exposure. The initial responses to the mirror-image were social in nature, as though the mirror image were an unfamiliar conspecific. Over the course of 2 to 3 days of mirror exposure, social behaviors waned, and behaviors that Gallup called “self-directed” began to occur. These self-directed behaviors included the use of the mirror to investigate and manipulate body areas (such as the face) that were otherwise invisible to the animal, as well as such behaviors as blowing bubbles or making faces while looking at the mirror-image. Gallup interpreted the demonstration of self-directed behaviors as indicating that the chimpanzees recognized themselves in the mirror; however, because of the potentially subjective nature of this interpretation, he devised a more objective test of self recognition, often called the “mark test.”