Monkeys are superior to men in this:
when a monkey looks into a mirror,
he sees a monkey.

The mirror test is a procedure to determine whether an animal is capable of self-recognition. In theory, self-recognition is predicated on self-awareness; in order to recognize myself in a mirror, I must first be able to grasp the concept of "myself." For centuries, humans believed they were alone in experiencing this aspect of consciousness. In 1970, psychologist Gordon G. Gallup devised the mirror test to prove that chimpanzees are also capable of self-recognition and thus, presumably, are self-aware. Since then, the mirror test has been performed on various species (including Homo sapiens), although many experts criticize the test's value.

The Test

Mirror self-recognition is at least partially a learned behavior. When first exposed to a mirror, most animals, including humans, react to their reflection as they would to another member of the same species (that is, if they react to the mirror at all). Many animals never progress beyond this stage. Humans, however, eventually learn to recognize their mirror image as a reflection of self, usually around the age of 18 to 24 months.

Gallup hypothesized that other hominids may possess the native faculties required for self-recognition, but lack sufficient learning opportunities to understand mirrors. To test this hypothesis, he isolated wild-born juvenile chimpanzees in cages located in empty rooms. A full-length mirror was placed in each room, in direct view (but out of reach) of the test subject. Researchers then observed the chimpanzees' behavior for 10 days, categorizing interactions with the mirror as either other-directed or self-directed.

Initially, the chimps responded to the mirror with other-directed actions, including head-bobbing, vocalization, and threatening gestures. By the third day, the chimps started exhibiting self-directed responses, using the mirror for the purposes of grooming, inspecting their teeth, and making silly faces. This self-directed behavior continued for the duration of the experiment, although the chimps' interest in the mirror waned as the novelty wore off. On the last day, the chimpanzees were anesthetized in order to surreptitiously mark parts of their faces with a bright red, odorless dye. Meanwhile, researchers removed the mirrors. Upon awakening, the chimps did not pay any special attention to the new marks. When granted access to a mirror, however, most of the chimps suddenly showed intense interest in their reflections, while repeatedly touching the marked parts of their own faces that were only visible in the mirror.

The mirror test subsequently became a widely used behavioral research tool, with slight variations in procedure, such as longer periods of exposure to the mirror and different species-specific mark locations. Also, most applications of the mirror test now use a control mark that is not directly or indirectly visible to the animal at all, often on the back of the test subject's head. This verifies that the animals can't detect the dye based on smell or feel.

The only non-humans that have definitely passed the mirror test are the great apes, with the possible exception of gorillas. Bottlenose dolphins and elephants may also be able to pass the mirror test, but so far, there haven't been any attempts to replicate those study results. There are also many controversial studies claiming that some monkeys and some birds can pass the mirror test under certain conditions, but these results are not consistently reproducible. Every other species tested has failed miserably.

The Critics

Some researchers, including Gallup, argue that passing the mirror test is evidence of superior cognitive abilities. Animal rights activists go so far as to claim that mirror self-recognition implies sentience (although technically, the mirror test is more closely linked to sapience rather than sentience), leading to numerous protracted legal battles to grant personhood to non-humans that pass the mirror test. Thus far, Brazilian courts have recognized a chimpanzee as a "legal subject" with the right to habeas corpus, Austrian courts rejected a similar petition to grant personhood to a chimp, and the Spanish parliament passed a law granting limited human rights to great apes.

However, a number of experts in the fields of psychology and animal behavior are skeptical of the mirror test. Criticism of the mirror test tends to fall into two camps: folks who believe that the methodology is flawed, and folks who believe that interpretation of the test results is flawed.

The simplest opposing argument is that failing the mirror test does not prove a lack of self-recognition. By its very nature, the test is biased in favor of visually oriented species with stereoscopic vision. Dogs, for example, are notorious for failing the mirror test. However, dogs also have relatively poor visual acuity, instead relying predominantly on their senses of smell and hearing. They don't recognize themselves in a mirror, but multiple studies have demonstrated that canines reliably recognize their own scent.

Many mirror test studies also unwittingly introduce the possibility of the "Clever Hans effect," a problem common in behavioral research on both humans and animals. Clever Hans was a horse with the apparent ability to perform basic arithmetic and correctly answer yes or no questions. In reality, Hans had learned to read subconscious nonverbal cues from his human audience. With a few exceptions (such as Gallup's original study on chimpanzees), mirror test experiments have used small sample sizes in environments that are not rigorously controlled, where test subjects have frequent contact with human handlers and observers who may unintentionally influence the animals' behavior.

Finally, in terms of methodology, the mirror test is terribly subjective. In the words of animal behaviorist and vocal mirror test skeptic Clive Wynne, "One researcher's 'chimp examining its ano-genital region with the aid of a mirror' is another scientist's chimp scratching his rear end because he has lost interest in the odd individual in the looking glass." This problem becomes even more pronounced when studying non-primates. Can we really tell whether a dolphin's reaction to a mirror is self-directed or other-directed?

Many scientists also cast doubt on the common interpretations of the mirror test results. Amongst primates, mirror self-recognition may depend more on socialization than on innate cognitive ability. For example, gorillas are the only great ape to fail the mirror test, possibly because gorillas display strong gaze aversion (direct eye contact is perceived as an act of hostility), and are also hypersensitive to the presence of human observers. The only gorilla to consistently pass a mark-directed mirror test is Koko, the media darling of the 70s and 80s who can hold rudimentary conversations in sign language. Koko was raised and educated by humans since infancy, a decidedly atypical upbringing for a gorilla. Conversely, unlike their wild-born and hand-reared brethren, chimpanzees that were raised in laboratory isolation consistently fail the mirror test. Native ability alone does not account for these results.

Then, of course, there is the basic question as to whether mirror self-recognition is related to self-awareness at all. Most of these arguments reference studies that applied the mirror test to humans, where self-awareness could be gauged through verbal questioning in addition to the mirror test results. Children with severe autism pass the mirror test, despite the fact that their condition involves impaired self-awareness. Some people with Alzheimer's and specific types of brain damage fail the mirror test, even though they are quite obviously self-aware. These results suggest that the mirror test may have more to do with face recognition than sense of self.

So what?

The concept behind the mirror test is undeniably interesting. As a tool for gauging self-recognition in other species, the mirror test is at least marginally better than, well, nothing at all. However, as a repeatable test for consistently and objectively detecting self-awareness under the rigors of the scientific method, the mirror test is deeply flawed. With the exception of a handful of scientists involved in the original research on chimps and mirrors, even proponents of the mirror test begrudgingly admit to these shortcomings.

Ultimately, the mirror test tells us far more about ourselves than about whatever species is being studied. The test's popularity is not due to its debatable scientific value, but to its cultural value. Though we call it a test for self-recognition, we use it as a test for humanity. We ascribe lofty, ill-defined notions like cognition and self-awareness to mirror self-recognition, and then pat ourselves on the back when our initial assumption holds true: we are (almost) as special as we've always suspected. A monkey looking into a mirror may see a monkey, but when we observe the monkey doing so, we both hope and fear to see Man.

Sources:

• Gallup, GG. "Self-recognition in primates: A comparative approach to the bidirectional properties of consciousness." American Psychologist. 32 (1977): 329-377.
• Gallup, GG, Anderson, JR, and Shillito, DJ. "The mirror test." The Cognitive Animal: Empirical and Theoretical Perspectives on Animal Cognition. Ed. Marc Bekoff, et al. Cambridge: MIT Press, 2002.
• Great Ape Project. http://greatapeproject.org
• Hall, L. and Waters, AJ. "From Property to Person: The Case of Evelyn Hart." GRASP - Great Ape Standing and Personhood. http://www.personhood.org/personhood/lawreview
• Hauser, MD, Kralik, J, et al. "Self-recognition in primates: phylogeny and the salience of species-typical features." Proceedings of the National Academy of Sciences. 92.23 (1995): 10811-10814.
• Wynne, C. "The soul of the ape." American Scientist. 89.2 (2001): 120.