The mirror test – sometimes called the mark test, mirror self-recognition test (MSR), red spot technique, or rouge test – is a behavioural technique developed in 1970 by psychologist Gordon Gallup Jr. as an attempt to determine whether an animal possesses the ability of visual self-recognition. The MSR test is the traditional method for attempting to measure self-awareness. However, there has been agreement that animals can be self-aware in ways not measured by the mirror test, such as distinguishing between their own and others' songs and scents. On the other hand, animals that can pass the MSR do not necessarily have self-awareness.
In the classic MSR test, an animal is anaesthetised and then marked (e.g. painted, or a sticker attached) on an area of the body the animal cannot normally see. When the animal recovers from the anesthetic, it is given access to a mirror. If the animal then touches or investigates the mark, it is taken as an indication that the animal perceives the reflected image as itself, rather than of another animal.
Very few species have passed the MSR test. As of 2016, only great apes (including humans), a single Asiatic elephant, dolphins, orcas, Giant oceanic manta rays and the Eurasian magpie have passed the MSR test. A wide range of species have been reported to fail the test, including several species of monkey, giant pandas, sea lions, and dogs.
- 1 Method and history
- 2 Animals that have passed
- 3 Animals that have failed
- 4 Animals that may pass
- 5 Other uses for mirrors
- 6 Robots
- 7 Criticism
- 8 Rouge test
- 9 See also
- 10 References
- 11 External links
Method and history
The inspiration for the mirror test comes from an anecdote about Charles Darwin and a captive orangutan. While visiting the London Zoo in 1838, Darwin observed an orangutan, named Jenny, throwing a tantrum after being teased with an apple by her keeper. This started him thinking about the subjective experience of an orangutan. He also watched Jenny gaze into a mirror and noted the possibility that she recognised herself in the reflection.
In 1970, Gordon Gallup, Jr., experimentally investigated the possibility of self-recognition with two male and two female wild pre-adolescent chimpanzees (Pan troglodytes), none of which had presumably seen a mirror previously. 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 behaviours was recorded upon introducing the mirrors to the chimpanzees. Initially, the chimpanzees made threatening gestures at their own images, ostensibly seeing their own reflections as threatening. Eventually, the chimps used their own reflections for self-directed responding behaviours, such as grooming parts of their body previously not observed without a mirror, picking their noses, making faces, and blowing bubbles at their own reflections.
Gallup expanded the study by manipulating the chimpanzees' appearance and observing their reaction to their reflection in the mirror. Gallup anaesthetised the chimpanzees and then painted a red alcohol-soluble dye on the eyebrow ridge and on the top half of the opposite ear. When the dye dried, it had virtually no olfactory or tactile cues. Gallup then returned the chimpanzees to the cage (with the mirror removed) and allowed them to regain full consciousness. He then recorded the frequency with which the chimpanzees spontaneously touched the marked areas of skin. After 30 minutes, the mirror was re-introduced into the room and the frequency of touching the marked areas again determined. The frequency of touching increased to 4–10 with the mirror present, compared to only 1 when the mirror had been removed. The chimpanzees sometimes inspected their fingers visually or olfactorily after touching the marks. Other mark-directed behaviour includes turning and adjusting of the body to better view the mark in the mirror, or tactile examination of the mark with an appendage while viewing the mirror.
An important aspect of the classical mark-test is that the mark/dye is non-tactile, preventing attention being drawn to the marking through additional perceptual cues (somesthesis). For this reason, animals in the majority of classical tests are anesthetised. Some tests use a tactile marker.
Animals that are considered to be able to recognise themselves in a mirror typically progress through four stages of behaviour when facing a mirror:
- social responses
- physical inspection (e.g. looking behind the mirror)
- repetitive mirror-testing behaviour
- realisation of seeing themselves
Gallup conducted a follow-up study in which two chimpanzees with no prior experience of a mirror were put under anesthesia, marked and observed. After recovery, they made no mark-directed behaviours either before or after being provided with a mirror.
The rouge test was also done by Michael Lewis and Jeanne Brooks-Gunn in 1979 for the purpose of self-recognition with human mothers and their children.
Animals that have passed
A large number of studies using a wide range of species have investigated the occurrence of spontaneous, mark-directed behaviour when given a mirror, as originally proposed by Gallup. Most marked animals given a mirror initially respond with social behaviour, such as aggressive displays, and continue to do so during repeated testing. Only a small number of species have touched or directed behaviour toward the mark, thereby passing the classic MSR test.
Findings in MSR studies are not always conclusive. Even in chimpanzees, the species most studied and with the most convincing findings, clear-cut evidence of self-recognition is not obtained in all individuals tested. Prevalence is about 75% in young adults and considerably less in young and aging individuals.
Until the 2008 study on magpies, self-recognition was thought to reside in the neocortex area of the brain. However, this brain region is absent in non-mammals. Self-recognition may be a case of convergent evolution, where similar evolutionary pressures result in similar behaviours or traits, although species arrive at them via different routes, and the underlying mechanism may be different.
- Bottlenose dolphin (Tursiops truncatus): Researchers in a study on two male bottlenose dolphins observed their reactions to mirrors after having a mark placed on them. Reactions such as decreased delay in approaching the mirror, repetitious head circling and close viewing of the eye or genital region which had been marked, were reported as evidence of MSR in these species.
- Killer whale (Orcinus orca): Killer whales and false killer whales (Pseudorca crassidens) may be able to recognise themselves in mirrors.
- Bonobo (Pan paniscus)
- Bornean orangutan (Pongo pygmaeus): However, mirror tests with a juvenile (2-year-old), male orangutan failed to reveal self-recognition.
- Chimpanzee (Pan troglodytes): However, mirror tests with a juvenile (11 months old) male chimpanzee failed to reveal self-recognition. Two young chimpanzees showed retention of MSR after one year without access to mirrors.
- Human (Homo sapiens): Humans begin to show self-recognition in the mirror test when they are about 18 months old, or in what psychoanalysts call the "mirror stage".
- Asian elephant (Elephas maximus): In a study performed in 2006 three female Asian elephants were exposed to a large mirror to investigate their responses. Visible marks and invisible sham-marks were applied to the elephants' heads to test whether they would pass the MSR test. One of the elephants showed mark-directed behaviour, though the other two did not. An earlier study failed to find MSR in two Asian elephants; it was claimed this was because the mirror was too small. The study was conducted with the Wildlife Conservation Society (WCS) using elephants at the Bronx Zoo in New York. All three Asian elephants in the study were standing in front of a 2.5 m-by-2.5 m mirror—they inspected the rear and brought food close to the mirror for consumption. Evidence of elephant self-awareness was shown when one (and only one) elephant, Happy, repeatedly touched a painted X on her head with her trunk, a mark which could only be seen in the mirror. Happy ignored another mark made with colorless paint that was also on her forehead to ensure she was not merely reacting to a smell or feeling. Frans De Waal, who ran the study, stated, "These parallels between humans and elephants suggest a convergent cognitive evolution possibly related to complex society and cooperation."
- Eurasian magpie (Pica pica): The Eurasian magpie is the first non-mammal to have passed the mirror test. Researchers applied a small red, yellow or black sticker to the throat of five Eurasian magpies, where they could be seen by the bird only by using a mirror. The birds were then given a mirror. The feel of the sticker on their throats did not seem to alarm the magpies. However, when the birds with coloured stickers caught a glimpse of themselves in the mirror, they scratched at their throats—a clear indication that they recognised the image in the mirror as their own. Those that received a black sticker, invisible against the black neck feathers, did not react.
- In a Belgian study from 2015, published in a predatory journal, by an author known for other controversial reports, 23 out of 24 adult ants scratched at small blue dots painted on their clypeus (part of their "face") when they were able to see the dot in a mirror. According to the purported results, the ants were individually tested and were from three species, Myrmica sabuleti, Myrmica rubra and Myrmica ruginodis. None of the ants scratched the clypeus when they had no mirror to see the dot. None tried to scratch the blue dot on the mirror. When they had a mirror and a brown dot similar to their own color, only one of thirty ants scratched the brown dot; researchers said she was darker than average so the dot was visible. They also reacted to the mirror itself. Even without dots, 30 out of 30 ants touched the mirror with legs, antennae and mouths, while 0 of 30 ants touched a clear glass divider, with ants on the other side. Ants a few days old did not react to the dots. These three species have limited eyesight, with 109–169 facets per eye, and the authors suggest doing tests on ants with more facets (some have 3,000) and on bees.
Animals that have failed
A range of species have been exposed to mirrors. Although these might have failed the classic MSR test, they have sometimes shown mirror-related behaviour:
- Sea lions (Zalophus californianus)
- Giant panda (Ailuropoda melanoleuca): In one study, 34 captive giant pandas of a wide range of ages were tested. None of the pandas responded to the mark and many reacted aggressively towards the mirror, causing the researchers to consider the pandas viewed their reflection as a conspecific.
- Gibbon (g. Hylobates, Symphalangus and Nomascus)
- Stump-tailed macaque (Macaca arctoides)
- Crab-eating macaque (Macaca fascicularis)
- Rhesus monkey (Macaca mulatta): It has been reported that rhesus monkeys exhibit other behaviours in response to a mirror which indicate self-recognition.
- Black-and-white colobus monkey (Colobus guereza)
- Capuchin monkey (Cebus paella)
- Hamadryas baboon (Papio hamadryas)
- Cotton-top tamarin (Saguinus oedipus)
- Octopuses oriented towards their image in a mirror, but there is no difference in their behaviour in this condition, compared with a view of other octopuses.
Animals that may pass
Findings for gorillas are mixed. At least four studies have reported that gorillas failed the MSR test. It has been suggested that the gorilla may be the only great ape "which lacks the conceptual ability necessary for self-recognition". Other studies have found more positive results, but have tested gorillas with extensive human contact, and required modification of the test by habituating the gorillas to the mirror and not using anaesthetic. Koko reportedly passed the MSR test, although this was without anaesthetic. In gorillas, protracted eye contact is an aggressive gesture and they may therefore fail the mirror test because they deliberately avoid making eye contact with their reflections. This could also explain why only gorillas with extensive human interaction and a certain degree of separation from other gorillas and usual gorilla behaviour are more predisposed to passing the test.
Two captive giant manta rays showed frequent, unusual and repetitive movements in front of a mirror suggested contingency checking. They also showed unusual self-directed behaviours when exposed to the mirror.
Other uses for mirrors
Primates, other than the great apes, have so far universally failed the mirror test. However, mirror tests with three species of gibbon (Hylobates syndactylus, H.gabriellae, H. leucogenys) have shown convincing evidence of self-recognition despite the fact that the animals failed the standard version of the mirror test.
Rhesus macaques have failed the MSR test, but use mirrors to study otherwise-hidden parts of their bodies, such as their genitals and the implants in their heads. It has been suggested this demonstrates at least a partial self-awareness, although this is disputed.
Pigs can use visual information seen in a mirror to find food, and show evidence of self-recognition when presented with their reflection. In an experiment, 7 of the 8 pigs tested were able to find a bowl of food hidden behind a wall and revealed using a mirror. The eighth pig looked behind the mirror for the food. BBC Earth also showed the foodbowl test, and the "matching shapes to holes" test, in the Extraordinary Animals series.
B. F. Skinner found that Pigeons are capable of passing a highly modified mirror test after extensive training. In the experiment, a pigeon was trained to look in a mirror to find a response key behind it, which the pigeon then turned to peck to obtain food. Thus, 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. However, untrained pigeons have never passed the mirror test.
Manta rays repeatedly swim in front of the mirror, turning over to show their undersides and moving their fins. When in front of the mirror, they blow bubbles, an unusual behaviour. They do not try to socially interact with the mirror image, suggesting that they recognise that the mirror image is not another ray. However, a classic mirror test using marks on the rays’ bodies has yet to be done.
The MSR test has been criticised for several reasons, in particular, because it may result in findings that are false negatives.
The MSR test may be of limited value when applied to species that primarily use senses other than vision.[verification needed] For example, dogs mainly use olfaction and audition; vision is used only third. It is suggested this is why dogs fail the MSR test. With this in mind, the biologist Marc Bekoff developed a scent-based paradigm using dog urine to test self-recognition in canines. He tested his own dog, but his results were inconclusive. Dog cognition researcher Alexandra Horowitz formalized Bekoff's idea in a controlled experiment, reported on in 2016 and published in 2017. She compared the dogs' behavior when examining their own and others' odors, and also when examining their own odor with an added smell "mark" analogous to the visual mark in MSR tests. These subjects not only discriminated their own odor from that of other dogs, as Bekoff had found, but also spent more time investigating their own odor "image" when it was modified, as subjects who pass the MSR test do. A 2016 study suggested an ethological approach, the "Sniff test of self-recognition (STSR)" which may shed light on different ways of checking for self-recognition.
Another concern with the MSR test is that some species quickly respond aggressively to their mirror reflection as if it were a threatening conspecific thereby preventing the animal to calmly consider what the reflection actually represents. It has been suggested this is the reason why gorillas and monkeys fail the MSR test.
In a MSR test, animals may not recognise the mark as abnormal, or, may not be sufficiently motivated to react to it. However, this does not mean they are unable to recognise themselves. For example, in a MSR test conducted on three elephants, only one elephant passed the test but the two elephants that failed still demonstrated behaviours that can be interpreted as self-recognition. The researchers commented that the elephants might not have touched the mark because it was not important enough to them. Similarly, lesser apes infrequently engage in self-grooming, which may explain their failure to touch a mark on their head in the mirror test.
Finally, it should be noted that there has been controversy over whether self-recognition implies self-awareness. The ant researchers state that many ants, from three species, pass the mirror test, but the researchers do not know that they have self-awareness. Dogs recognize their own scent as different from others' scents, but fail the mirror test.
The rouge test is a version of the mirror test used with human children. Using rouge makeup, an experimenter surreptitiously places a dot on the face of the child. The child is then placed in front of a mirror and their reactions are monitored; depending on the child's development, distinct categories of responses are demonstrated. This test is widely cited as the primary measure for mirror self-recognition in human children.
From the age of 6 to 12 months, the child typically sees a "sociable playmate" in the mirror's reflection. Self-admiring and embarrassment usually begin at 12 months, and at 14 to 20 months most children demonstrate avoidance behaviours. Finally, at 18 months half of children recognise the reflection in the mirror as their own and by 20 to 24 months self-recognition climbs to 65%. Children do so by evincing mark-directed behaviour; they touch their own nose or try to wipe the mark off.
It appears that self-recognition in mirrors is independent of familiarity with reflecting surfaces. In some cases the rouge test has been shown to have differing results, depending on sociocultural orientation. For example, a Cameroonian Nso sample of infants 18 to 20 months of age had an extremely low amount of self-recognition outcomes at 3.2%. The study also found two strong predictors of self-recognition: object stimulation (maternal effort of attracting the attention of the infant to an object either person touched) and mutual eye contact. A strong correlation between self-concept and object permanence have also been demonstrated using the rouge test.
The rouge test is a measure of self-concept; the child who touches the rouge on his own nose upon looking into a mirror demonstrates the basic ability to understand self-awareness. Animals, young children, and people who have their sight restored after being blind from birth, sometimes react to their reflection in the mirror as though it were another individual.
Theorists have remarked on the significance of this period in a child's life. For example, psychoanalyst Jacques Lacan used a similar test in marking the mirror stage when growing up. Current views of the self in psychology position the self as playing an integral part in human motivation, cognition, affect, and social identity.
There is some debate as to the interpretation of the results of the mirror test, and researchers in one study have identified some potential problems with the test as a means of gauging self-awareness in young children and animals.
Proposing that a self-recognising child or animal may not demonstrate mark-directed behaviour because they are not motivated to clean up their faces, thus providing incorrect results, the study compared results of the standard rouge test methodology against a modified version of the test.
In the classic test, the experimenter first played with the children, making sure that they looked in the mirror at least three times. Then, the rouge test was performed using a dot of rouge below the child's right eye. For their modified testing, the experimenter introduced a doll with a rouge spot under its eye and asked the child to help clean the doll. The experimenter would ask up to three times before cleaning the doll themselves. The doll was then put away, and the mirror test performed using a rouge dot on the child's face. These modifications were shown to increase the number of self-recognisers.
The results uncovered by this study at least suggest some issues with the classic mirror test; primarily, that it assumes that children will recognise the dot of rouge as abnormal and attempt to examine or remove it. The classic test may have produced false negatives, because the child's recognition of the dot did not lead to them cleaning it. In their modified test, in which the doll was cleaned first, they found a stronger relationship between cleaning the doll's face and the child cleaning its own face. The demonstration with the doll, postulated to demonstrate to the children what to do, may lead to more reliable confirmation of self-recognition.
On a more general level, it remains debatable whether recognition of one's mirror image implies self-awareness. Likewise, the converse may also be false—one may hold self-awareness, but not present a positive result in a mirror test.
- Gallup, GG Jr. (1970). "Chimpanzees: Self recognition". Science. 167 (3914): 86–87. Bibcode:1970Sci...167...86G. doi:10.1126/science.167.3914.86. PMID 4982211.
- Bekoff, Marc (2002-09-19). "Animal reflections" (PDF). Nature.
- Cammaerts, Marie-Claire, and Roger Cammaerts (2015-07-01). "Are ants (Hymenoptera, Formicidae) capable of self recognition?" (PDF). Journal of Science. 5 (7): 521–532.
- "List of Animals That Have Passed the Mirror Test". 2015-04-15. Retrieved 23 November 2015.
- Turner, Rebecca. "10 Animals with Self Awareness". Retrieved 23 November 2015.
- Jonathan Weiner. Darwin at the Zoo. available at http://www.scientificamerican.com/article.cfm?id=darwin-at-the-zoo.
- Carl Zimmer. The Descent of Man: The Concise Edition. excerpt available at http://carlzimmer.com/books/descentofman/excerpt.html.
- Mitchell, R.W. (1995). "Evidence of dolphin self-recognition and the difficulties of interpretation". Consciousness and Cognition. 4 (2): 229–234. doi:10.1006/ccog.1995.1029. PMID 8521261.
- Plotnik, J.M., de Waal, F.B.M. and Reiss, D. (2006). "Self-recognition in an Asian elephant". Proceedings of the National Academy of Sciences. 103 (45): 17053–17057. Bibcode:2006PNAS..10317053P. doi:10.1073/pnas.0608062103. PMC 1636577. PMID 17075063.
- Shaffer, David (2009). Social and Personality Development. Belmont: Thomson Wadsworth. p. 172. ISBN 978-0-495-60038-1.
- Prior, H., Schwarz, A. and Güntürkün, O. (2008). "Mirror-induced behavior in the magpie (Pica pica): Evidence of self-recognition" (PDF). PLoS Biology. 6 (8): e202. doi:10.1371/journal.pbio.0060202. PMC 2517622. PMID 18715117. Archived from the original (PDF) on 19 November 2008.
- Povinelli, D.J., Rulf, A.B., Landau, K.R. and Bierschwale, D.T. (1993). "Self-recognition in chimpanzees (Pan troglodytes): distribution, ontogeny, and patterns of emergence". J. Comp. Psychol. 107 (4): 347–372. doi:10.1037/0735-7036.107.4.347. PMID 8112048.
- Suddendorf, T. & Collier-Baker, E. (2009). "The evolution of primate visual self-recognition: Evidence of absence in lesser apes" (PDF). Proc. R. Soc. B. 276 (1662): 1671–1677. doi:10.1098/rspb.2008.1754. PMC 2660989. PMID 19324830.
- Marten, K. & Psarakos, S. (1995). "Evidence of self-awareness in the bottlenose dolphin (Tursiops truncatus)". In Parker, S.T.; Mitchell, R. & Boccia, M. Self-awareness in Animals and Humans: Developmental Perspectives. Cambridge University Press. pp. 361–379. Archived from the original on 13 October 2008.
- Reiss, D. & Marino, L. (2001). "Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence". Proceedings of the National Academy of Sciences. 98 (10): 5937–5942. Bibcode:2001PNAS...98.5937R. doi:10.1073/pnas.101086398. PMC 33317. PMID 11331768.
- Delfour, F. & Marten, K. (2001). "Mirror image processing in three marine mammal species: Killer whales (Orcinus orca), false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus)". Behavioural Processes. 53 (3): 181–190. doi:10.1016/s0376-6357(01)00134-6. PMID 11334706.
- Walraven, V., van Elsacker, L. and Verheyen, R. (1995). "Reactions of a group of pygmy chimpanzees (Pan paniscus) to their mirror images: evidence of self-recognition". Primates. 36: 145–150. doi:10.1007/bf02381922.
- Greg C. Westergaard; C. W. Hyatt (1994). "The responses of bonobos (Pan paniscus) to their mirror images: Evidence of self-recognition". Human Evolution. 9 (4): 273–279. doi:10.1007/BF02435514.
- Suárez, S.D. & Gallup, G.G. (1981). "Self-recognition in chimpanzees and orangutans, but not gorillas". Journal of Human Evolution. 10 (2): 175–188. doi:10.1016/s0047-2484(81)80016-4.
- Robert, S. (1986). "Ontogeny of mirror behavior in two species of great apes". American Journal of Primatology. 10 (2): 109–117. doi:10.1002/ajp.1350100202.
- Miller, J. (2009). "Minding the animals: Ethology and the obsolescence of left humanism". American Chronicle. Retrieved 21 May 2009.
- Povinelli, D.; de Veer, M.; Gallup Jr., G.; Theall, L.; van den Bos, R. (2003). "An 8-year longitudinal study of mirror self-recognition in chimpanzees (Pan troglodytes)". Neuropsychologia. 41 (2): 229–334. doi:10.1016/S0028-3932(02)00153-7. ISSN 0028-3932.
- Calhoun, S. & Thompson, R.L. (1988). "Long-term retention of self-recognition by chimpanzees". Am. J. Primatol. 15 (4): 361–365. doi:10.1002/ajp.1350150409.
- Archer, John (1992). Ethology and Human Development. Rowman & Littlefield. ISBN 978-0-389-20996-6.
- "Consciousness and the Symbolic Universe"
- Povinelli, D.J. (1989). "Failure to find self-recognition in Asian elephants (Elephas maximus) in contrast to their use of mirror cues to discover hidden food". Journal of Comparative Psychology. 103 (2): 122–131. doi:10.1037/0735-7036.103.2.122.
- "Elephants' Jumbo Mirror Ability". BBC News. 2006-10-31. Retrieved 2007-10-31.
- Uchino, Emiko; Watanabe, Shigeru (2014-11-01). "Self-recognition in pigeons revisited". Journal of the Experimental Analysis of Behavior. 102 (3): 327–334. doi:10.1002/jeab.112. ISSN 1938-3711. PMID 25307108.
- Kulick, Don (2017). "Human–Animal Communication" (PDF). Annual Review of Anthropology. 46 (1): 357–378. doi:10.1146/annurev-anthro-102116-041723.
- De Agrò, Massimo; Regolin, Lucia; Moretto, Enzo. "Visual Discrimination Learning in the Jumping Spider Phidippus regius" (PDF). Animal Behavior and Cognition. 4 (4): 413–424.
- "A species of fish has passed the mirror test for the first time".
- Kohda, Masanori; Takashi, Hatta; Takeyama, Tmohiro; Awata, Satoshi; Tanaka, Hirokazu; Asai, Jun-ya; Jordan, Alex (2018-08-21). "Cleaner wrasse pass the mark test. What are the implications for consciousness and self-awareness testing in animals?". bioRxiv: 397067. doi:10.1101/397067.
- Hill, H.M., Webber, K., Kemery, A., Garcia, M. and Kuczaj, S.A. (2015). "Can sea lions' (Zalophus californianus) use mirrors to locate an object?". International Journal of Comparative Psychology. 28.
- Ma, X., Jin, Y., Luo, B., Zhang, G., Wei, R. and Liu, D. (2015). "Giant pandas failed to show mirror self-recognition". Animal Cognition. 18 (3): 713–721. doi:10.1007/s10071-015-0838-4. PMID 25609263.
- Hyatt, C.W. (1998). "Responses of gibbons (Hylobates lar) to their mirror images". American Journal of Primatology. 45 (3): 307–311. doi:10.1002/(SICI)1098-2345(1998)45:3<307::AID-AJP7>3.0.CO;2-#. PMID 9651653.
- Rajala, A.Z., Reininger, K.R., Lancaster, K.M. and Populin, L.C. (2010). "Rhesus monkeys (Macaca mulatta) do recognize themselves in the mirror: Implications for the evolution of self-recognition". PLoS ONE. 5 (9): e12865. Bibcode:2010PLoSO...512865R. doi:10.1371/journal.pone.0012865. PMC 2947497. PMID 20927365.
- Shaffer, V. A., & Renner, M. J. (2002). "Black and white colobus monkeys (Colobus guereza) do not show mirror self-recognition". International Journal of Comparative Psychology. 13: 154–159.
- Roma, P., Silberberg, A., Huntsberry, M., Christensen, C., Ruggiero, A. and Suomi, S. (2007). "Mark tests for mirror self-recognition in Capuchin monkeys (Cebus Apella) trained to touch marks". American Journal of Primatology. 69 (9): 989–1000. doi:10.1002/ajp.20404. ISSN 0275-2565. PMID 17253635.
- M. Hauser, C. Miller, K. Liu, R. Gupta (2001). "Cotton‐top tamarins (Saguinus oedipus) fail to show mirror‐guided self‐exploration". American Journal of Primatology. 137 (December 2000): 131–137. doi:10.1002/1098-2345(200103)53:3<131::AID-AJP4>3.0.CO;2-X.
- Davies, E. (20 September 2011). "Crows use mirrors to find food". BBC Nature. Retrieved 19 May 2012.
- Soler, M., Pérez-Contreras, T. and Peralta-Sánchez, J.M. (2014). "Mirror-mark tests performed on jackdaws reveal potential methodological problems in the use of stickers in avian mark-test studies". PLoS ONE. 9 (1): e86193. Bibcode:2014PLoSO...986193S. doi:10.1371/journal.pone.0086193. PMC 3903501. PMID 24475085.
- Kraft F.L., Forštová T., Utku Urhan A., Exnerová A., Brodin A. (2017). "No evidence for self-recognition in a small passerine, the great tit (Parus major) judged from the mark/mirror test". Animal Cognition. 20 (6). pp. 1049–1057. doi:10.1007/s10071-017-1121-7. PMC 5640729.
- Hotta T, Komiyama S, Kohda M (2018). "A social cichlid fish failed to pass the mark test". Animal Cognition. 21 (1). pp. 127–136. doi:10.1007/s10071-017-1146-y. PMID 29150813.
- Mather Jennifer A.; Kuba Michael J. (2013). "The cephalopod specialties: complex nervous system, learning, and cognition" (PDF). Canadian Journal of Zoology. 91 (6): 445. doi:10.1139/cjz-2013-0009. Archived from the original (PDF) on 26 February 2016.
- Shillito, D., Gallup, G.G. and Beck, B.B. (1999). "Factors affecting mirror behaviour in western lowland gorillas, Gorilla gorilla". Animal Behaviour. 57 (5): 999–1004. doi:10.1006/anbe.1998.1062. PMID 10328785.
- Ledbetter, D.H. & Basen, J.A. (1982). "Failure to demonstrate self-recognition in gorillas". American Journal of Primatology. 2 (3): 307–310. doi:10.1002/ajp.1350020309.
- Nicholson, I.S. & Gould, J.E. (1995). "Mirror mediated object discrimination and self-directed behavior in a female gorilla". Primates. 36 (4): 515–521. doi:10.1007/bf02382873.
- Allen, M. & Schwartz, B.L. (2008). "Mirror self-recognition in a Gorilla (Gorilla gorilla gorilla)" (PDF). J. Integr. Biosci. 5: 19–24. doi:10.1037/e603982013-032.
- Posada, S. & Colell, M. (2007). "Another gorilla (Gorilla gorilla gorilla) recognizes himself in a mirror". American Journal of Primatology. 69 (5): 576–583. doi:10.1002/ajp.20355. PMID 17154375.
- Patterson, F. & Gordon, W. (1993). "The case for personhood of gorillas". In Cavalieri, P. & Singer, P. The Great Ape Project. St. Martin's Griffin. pp. 58–77.
- Kind, Amy (2015-10-02). Persons and Personal Identity. John Wiley & Sons. ISBN 9781509500246.
- Ari, C. and D’Agostino, D.P. (2016). "Contingency checking and self-directed behaviors in giant manta rays: Do elasmobranchs have self-awareness?". Journal of Ethology. 34 (2): 167–174. doi:10.1007/s10164-016-0462-z.
- Ujhelyi, M., Merker, B., Buk, P. and Geissmann, T. (2000). "Observations on the behavior of gibbons (Hylobates leucogenys, H. gabriellae, and H. lar) in the presence of mirrors". Journal of Comparative Psychology. 114 (3): 253–262. doi:10.1037/0735-7036.114.3.253. PMID 10994841.
- Brandon, K. (29 September 2010). "Monkeys see selves in mirror, open a barrel of questions". Wired. Retrieved 1 October 2010.
- Broom, D. M.; Sena, H.; Moynihan, K. L. (2009). "Pigs learn what a mirror image represents and use it to obtain information". Animal Behaviour. 78 (5): 1037–1041. doi:10.1016/j.anbehav.2009.07.027.
- Epstein, L., Skinner, R.P. and Skinner, B.F. (1981). ""Self-awareness" in the pigeon". Science. 212 (4495): 695–696. Bibcode:1981Sci...212..695E. doi:10.1126/science.212.4495.695. PMID 17739404.
- This is video of one such test
- De Waal, F.B. (2008). "The thief in the mirror". PLOS Biology. 6 (8): e201. doi:10.1371/journal.pbio.0060201. PMC 2517621. PMID 18715116.
- Amanda Pachniewska (2016). "List of Animals That Have Passed the Mirror Test". Animalcognition.org.
- "Robot learns to recognise itself". BBC News. 2012-08-23.
- Stanley Coren (2004). How Dogs Think. ISBN 978-0-7432-2232-7.
- "Does My Dog Recognize Himself in a Mirror?".
- Horowitz, Alexandra (2016). Being a dog : following the dog into a world of smell. New York: Scribner. ISBN 9781476795997.
- Horowitz, Alexandra (2017). "Smelling themselves: Dogs investigate their own odours longer when modified in an "olfactory mirror" test". Behavioural Processes. 143C: 17–24. doi:10.1016/j.beproc.2017.08.001. PMID 28797909.
- "Can Dogs Smell Their 'Reflections'?". 17 August 2017. Retrieved 4 July 2018.
- Cazzolla Gatti, Roberto (2016). "Self-consciousness: beyond the looking-glass and what dogs found there". Ethology Ecology & Evolution. 28 (2): 232–240. doi:10.1080/03949370.2015.1102777. ISSN 0394-9370.
- Couchman, J.J. (2011). "Self-agency in rhesus monkeys". Biology Letters. 8 (1): 39–41. doi:10.1098/rsbl.2011.0536. PMC 3259954. PMID 21733868.
- Anderson, J.R. (1984). "Monkeys with mirrors: Some questions for primate psychology". International Journal of Primatology. 5 (1): 81–98. doi:10.1007/bf02735149.
- "Kids (and animals) who fail classic mirror tests may still have sense of self". 29 November 2010. Retrieved 30 May 2013.
- Hearne, Vicki (2007). Animal happiness : a moving exploration of animals and their emotions. New York: Skyhorse Pub. ISBN 9781602391673. OCLC 785423631.
- Beulah Amsterdam (1972). "Mirror self-image reactions before age two". Developmental Psychobiology. 5 (4): 297–305. doi:10.1002/dev.420050403. PMID 4679817.
- Lewis, M.; Brooks-Gunn, J. (1979). Social cognition and the acquisition of self. New York: Plenum Press. p. 296. ISBN 978-0-306-40232-6.
- Priel, Beatrice; de Schonen, Scania (1986). "Self-Recognition: A Study of a Population without Mirrors". Journal of Experimental Child Psychology. 41 (2): 237–250. doi:10.1016/0022-0965(86)90038-X. PMID 3701250.
- Sedikides, C. & Spencer, S.J. (Eds.) (2007). The Self. New York: Psychology Press
- Heidi Keller; Relindis Yovsi; Joern Borke; Joscha Kärtner; Henning Jensen; Zaira Papaligoura (2004). "Developmental Consequences of Early Parenting Experiences: Self-Recognition and Self-Regulation in Three Cultural Communities". Child Development. 75 (6): 1745–1760. doi:10.1111/j.1467-8624.2004.00814.x. PMID 15566377.
- BENNETT I. BERTENTHAL; KURT W. FISCHER (1978). "Development of Self-Recognition in the Infant" (PDF). Developmental Psychology (Submitted manuscript). 14: 44–50. CiteSeerX 10.1.1.550.1903. doi:10.1037/0012-1622.214.171.124.
- Amsterdam B (1972). "Mirror self-image reactions before age two". Dev Psychobiol. 5 (4): 297–305. doi:10.1002/dev.420050403. PMID 4679817.
- Brown, Jonathon (2014-06-03). Self-awareness in the first few weeks of life. ISBN 9781136872006. Retrieved November 4, 2017.
- Social Psychology, 6th Edition p68-69
- Lacan, J., Some reflections on the Ego in Écrits, org. published 1949.
- Asendorpf, J.B., Warkentin V. and Baudonniere, P. (1996). "Self-awareness and other-awareness II: Mirror self-recognition, social contingency awareness, and synchronic imitation". Developmental Psychology. 32 (2): 313–321. doi:10.1037/0012-16126.96.36.1993.
- List of animals who passed the mirror test and promising candidates on animalcognition.org
- The World First Self-Aware Robot and the Success of Mirror Image Cognition (Lecture at the Karlsruhe University and the Munich University, Germany), 8 November 2006.
- Elephants pass mirror test of self-awareness (The Guardian)
- Elephants' jumbo mirror ability (BBC News)
- Elephant study published in Proceedings of National Academy of Sciences, USA
- Elephants see themselves in the mirror (Newscientist.com with video)
- Can a robot pass the mirror test? – Raúl Arrabales Moreno, 2010-01-08