The mirror test is an experiment developed in 1970 by psychologist Gordon Gallup Jr. to determine whether an animal possesses the ability to recognize itself in a mirror. It is the primary indicator of self-awareness in non-human animals and marks entrance to the mirror stage by human children in developmental psychology.
The classic mirror test is performed by surreptitiously marking the animal with two scentless dye spots. The “test” spot is put on a part of the animal that would only be visible to it through use of a mirror; the “control” spot is on an accessible but completely visually hidden part of the animal’s body. If the animal reacts in a manner consistent with awareness that the test dye is located on its own body, yet ignores the control dye, it can be arguably concluded that the animal recognizes the mirror as an image of itself. Such behavior includes turning and adjusting of the body in order to better view the marking in the mirror, or tactile examination of the marking with a limb while viewing the mirror.
Several species of animals have been documented to pass the mirror test. Children gain the ability to pass the mirror test around 18 months of age. A specific version of the mirror test called the rouge test involves the use of rouge makeup as a test spot and assess the degree of self-awareness based on the child’s response to his or her mirror image.It has also been noted that some animals, young children, and people who have their sight restored after being blind from birth, often (at least initially) react to their reflection in the mirror as though it were another individual.
In 1970, Gordon Gallup Jr. reenacted Darwin’s initial experiment with two male and two female wild preadolescent chimpanzees, none of whom had presumably ever come into contact with a mirror prior to the experiment. Each chimpanzee was put into a room by itself for two days. Next, a full length mirror was placed in the room for a total of 80 hours at periodically decreasing distances. A multitude of behaviors were recorded upon introducing the mirrors to these wild chimpanzees.
Initially, the chimpanzees made threatening gestures at their own images, ostensibly seeing their own reflections as threatening. Eventually, the chimps used their own projected images for self-directed responding behaviors, such as grooming parts of the body before unseen without a mirror, picking their noses, making faces, and blowing bubbles at their own reflections. Gallup expanded the experiment by manipulating the chimpanzee’s appearance and observing its reaction to the mirror.
Gallup built on these observations to devise what is now commonly known as the mirror test, a method to gauge the self-awareness of an animal by determining whether it recognizes its own reflection in a mirror.