Mirror test

The test was developed by Gordon Gallup Jr. in 1970, based in part on observations made by Charles Darwin. While visiting a zoo, Darwin held a mirror up to an orangutan and recorded the animal's reaction, which included making a series of facial expressions. Darwin noted that the significance of these expressions was ambiguous, and could either signify that the primate was making expressions at what it perceived to be another animal, or it could be playing a sort of game with a new toy.

Gallup built on these observations by devising a test that attempts to gauge self-awareness by determining whether an animal can recognize its own reflection in a mirror as an image of itself. This is accomplished by surreptitiously marking the animal with two odourless dye spots. The test spot is on a part of the animal that would be visible in front of a mirror, while the control spot is in an accessible but hidden part of the animal's body. Scientists observe that the animal reacts in a manner consistent with it being aware that the test dye is located on its own body while ignoring the control dye. Such behaviour includes turning and adjusting of the body in order to better view the marking in the mirror, or poking at the marking on its own body with a limb while viewing the mirror.

At first, even animals that are capable of passing the mirror test respond as the orangutan described by Darwin. chimpanzees, orangutans, humans, and gorillas), bottlenose dolphins, orcas, elephants, and European Magpies. Initially, it was thought that gorillas did not pass the test, but there are now several well-documented reports of gorillas (such as Koko) passing the test. Other primates have so far failed the mirror test, though rhesus macaques demonstrated a behavior indicative of at least a partial self-awareness.

In 1981, Epstein, Lanza and Skinner published a paper in the journal Science in which they argued that the pigeon also passes the mirror test. A pigeon was trained to look in a mirror to find a response key behind it which the pigeon then turned to peck - food was the consequence of a correct choice (i.e., the pigeon learned to use a mirror to find critical elements of its environment). Next, the pigeon was trained to peck at dots placed on its feathers; food was, again, the consequence of touching the dot. The latter training was accomplished in the absence of the mirror. The final test was placing a small bib on the pigeon - enough to cover a dot placed on its lower belly. A control period without the mirror present yielded no pecking at the dot. When the mirror was revealed, the pigeon became active, looked in the mirror and then tried to peck on the dot under the bib. It is true that untrained pigeons have never been able to pass the mirror test. However, pigeons do not normally have access to mirrors and do not have the necessary experiences to use them. Giving the pigeons this experience did not guarantee that they would pass the mirror test; the pigeon never pecked dots on its own body in the presence of the mirror (until the final test). In addition, magpies have been shown to pass the test by trying to remove a coloured sticker from underneath their beaks when shown it in a mirror.

Dogs, cats, and young human babies tend to initially fail the mirror test.

Capuchin monkeys react to their reflection either with hostility or affection, and mark test experiments have shown that they are incapable of spontaneous mirror self-recognition. Similar tests performed using video technology support these findings, but suggest that the monkeys possess the raw input systems required for explicit self-recognition.

Pigs are also able to pass a variation of the mirror test. 7 of the 8 pigs tested were able to find a bowl of food hidden behind a wall using a mirror. The eighth pig looked behind the mirror for the food.

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