The mirror test of self-awareness

Only a handful of species have been shown to possess the ability of visual self-recognition

The mirror test, developed in 1970 by evolutionary psychologist Gordon Gallup, State University of New York, is used to test whether or not an animal possesses the ability of visual self-recognition. Only a handful of species have passed the mirror test, most recently a coral reef fish, the cleaner wrasse (Labroides dimidiatus), as reported in PLOS Biology by Masanori Kohda and others, on February 7th. This fish is a symbiotic groomer, eating parasites that live on other fish.

The mirror test is simple – make a mirror available to the animal and watch how it behaves. When the animal gets used to the mirror, put a mark on part of its body that cannot be viewed without the aid of the mirror. Now observe whether the animal is curious about its reflection and whether it realises that the mark is not part of itself.

Gorillas who have had extensive contact with humans come closer to passing the test than gorillas who have had limited contact with humans

Although some researchers claim that only humans and great apes conclusively pass the mirror mark test, the following species are generally regarded as capable of passing the mirror test – humans, bottlenose dolphins, killer whales, bonobos, orangutans, chimpanzees, Asian elephants, magpies, pigeons, ants and the cleaner wrasse fish. A human will not pass the mirror test until he/she is about two years old. Species such as dogs, cats, horses, parrots, sea lions, octopus and even monkeys have not been shown to pass the mirror test.

Mirror test results with gorillas are mixed. Gorillas who have had extensive contact with humans come closer to passing the test than gorillas who have had limited contact with humans. But the picture is clouded by the fact that gorillas interpret eye to eye contact as a sign of aggression and may avoid making eye contact with their mirror image.


Recognises the image

The Wikipedia entry on the mirror test hosts a fascinating video of a magpie passing the mirror test. A small red dot is applied to the magpie’s throat, visible only by using the mirror. When the bird sees the red dot in the mirror it scratches at its throat, indicating that it recognises the image in the mirror as its own. The bird remains unaffected when a black dot that merges in with its plumage is applied to its throat.

If you can't track your own thoughts and feelings, then you can't take account of others' self-awareness

An animal that passes the mirror test is capable of self-recognition and probably some level of self-awareness. This has important psychological/philosophical implications, as discussed by Benjamin Mitchell-Yellin in Psychology Today. The capacity for self-recognition is a necessary precondition to recognising that others can also recognise themselves and can recognise you.

If you can’t track your own thoughts and feelings, then you can’t take account of others’ self-awareness. Self-awareness is essential to allow one to participate in the negotiations involved in sophisticated social co-operation and in a moral community. As Mitchell-Yellin points out: if not every self-recogniser is a moral animal, all moral animals are self-recognisers.

Animals that pass the mirror test have large brains relative to body size and have higher levels of empathy and social awareness, co-operating with and caring for animals around them. You might wonder about ants, but the brains of some ant species constitutes 15 per cent of body mass.

‘Olfactory mirror’

The mirror test obviously depends on sight and some researchers think this test is unfair on species such as dogs or elephants, who rely so much on sense of smell. An “olfactory mirror” test was tried with dogs that involved altering the scent of the dog’s urine. It is more difficult to interpret the results of these tests, however.

Some researchers remain sceptical about whether or not the cleaner wrasse fish has really passed the mirror test. These fishes had a brown mark injected on their throats and were then observed to scrape their throats on a hard surface. They didn’t scrape their throats when a colourless mark was injected. The fish under test also displayed unusual behaviour such as swimming upside down in front of the mirror. Gordon Gallup thinks the experiment was flawed because it had no control group of fish with no prior exposure to the mirror.

Finally, don’t forget to watch the magpie on the Wikipedia link I cited earlier – it will greatly cheer you up.

William Reville is an emeritus professor of biochemistry at UCC

William Reville

William Reville

William Reville, a contributor to The Irish Times, is emeritus professor of biochemistry at University College Cork