Editor's Note: While I'm on vacation, I've arranged a series of guest posts from other writers who routinely cover animal behavior and cognition. Today's post, about the controversial mirror self-recognition test in primates, comes from the blogger at Serious Monkey Business. Follow her on twitter: @SrsMonkeyBiz.

I have a confession: one of my favorite things on the news is some of the fluff pieces—specifically, whenever animal cognition stories come up. Truthfully, I don’t believe they should be considered as fluff just because it isn’t anthropocentric, but this is an entirely different matter. While I enjoy these stories and associated articles, there is a bone I have to pick with animal cognition studies and the results sometimes derived from them:

In the words of the infamous Donald Rumsfeld, “The absence of evidence is not the evidence of absence.” In short: though sometimes cognitive tests may not give reason to think the subject has the cognitive capacity for which it is being tested, this does not necessarily mean it does not have these abilities. Maybe it just means it wasn't measured the right way.

Recent findings in multiple animals give us reason to reconsider the significance of an animal failing a cognition test.

One of the more famous examples of cognition tests is the mirror test to examine self-recognition in an individual. The test is usually performed by placing a small dab of non-toxic paint (or some other differently colored substance) across the individual’s forehead; if the individual is able to use a mirror to detect the dab, it is thought the individual has the ability to recognize itself.

Self-recognition in primates generally differs across the board; all great apes are able to recognize themselves in a mirror with varying frequencies. 43% of chimpanzees, 31% of gorillas, and 50% of orangutans pass this test (Swartz et al. 1999). The lesser apes, gibbons, typically fail the test and other primates (capuchins, tamarins, squirrel monkeys, and ring-tailed lemurs) generally fail the test (Hyatt 1998; Roma et al. 2007; Marchal & Anderson 1993; Inoue-Nakamura 1997). Three types of macaques (rhesus, cynomolgus, and stumptailed) are thought to fail the test, not having any self-directed behaviors with help from the mirror or investigate marks (Gallup 1970).

With that in mind, these tests give the impression macaques may not be as cognitively advanced as the great apes. A study published by Rajala and colleagues (2010) from the University of Wisconsin-Madison suggests otherwise. In this study, Rajala discovered two instances in which rhesus macaques used a mirror to aide in self-directed behaviors. In addition to observing himself in the mirror, one of the monkeys was able to “smell, lick, and look at his fingers while grooming in front of the mirror,” suggesting the individual was able to recognize himself through use of the mirror. Another monkey showed similar behaviors in examining a head cap it was wearing that was used for an electrophysiological experiment.

Certainly, at this time, this example only remains as an anecdote. But there are others that perceive the mirror test may be an incorrect barometer of self-recognition.

A study performed by Broom, Sena, and Moynihan (2009) gave reason to believe the mirror test is perhaps unfair to species which rely more on scent than sight. In tests given to pigs, researchers adjusted the typical test by adding food to appeal to the olfactory senses by adding a recognized food dish. By showing the pigs a familiar food bowl reflected in a mirror, but hidden behind a barrier, the pigs would only be able to find the food by understanding that mirrors displayed a visual reflection, rather than the item itself. They used a fan to fill the entire room with the scent of the food, so that the pigs would not be able to use olfactory cues to find it. In these tests, 7 out of 8 pigs were able to find the food bowl, suggesting modifications to the mirror test may be required in order to detect self-recognition accordingly.

The mirror test is far from perfect, but instead of recognizing it as a gauge of self-recognition, perhaps we ought to be viewing it as reflecting the ability to use environmental cues to notice that something is different or unexpected - rather than as a form of self-awareness. In other words, perhaps the mirror test simply assesses whether an animal understands the function of a mirror.

Broom, D., Sena, H., & Moynihan, K. (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

Gallup, G. (1970). Chimpanzees: Self-Recognition Science, 167 (3914), 86-87 DOI: 10.1126/science.167.3914.86

Hyatt CW (1998). Responses of gibbons (Hylobates lar) to their mirror images. American journal of primatology, 45 (3), 307-11 PMID: 9651653

Marchal P, & Anderson JR (1993). Mirror-image responses in capuchin monkeys (Cebus capucinus): social responses and use of reflected environmental information. Folia primatologica; international journal of primatology, 61 (3), 165-73 PMID: 8206423

Rajala AZ, Reininger KR, Lancaster KM, & Populin LC (2010). Rhesus monkeys (Macaca mulatta) do recognize themselves in the mirror: implications for the evolution of self-recognition. PloS one, 5 (9) PMID: 20927365

Roma PG, Silberberg A, Huntsberry ME, Christensen CJ, Ruggiero AM, & Suomi SJ (2007). Mark tests for mirror self-recognition in capuchin monkeys (Cebus apella) trained to touch marks. American journal of primatology, 69 (9), 989-1000 PMID: 17253635

Swartz, K.B., Sarauw, D., Evans, S. (1999). Comparative aspects of mirror self-recognition in great apes. In Parker, S.T., Mitchell, R.W., Miles, H.L., (Eds.), The mentalities of gorillas and orangutans: comparative perspectives. New York: Cambridge U. Press.

Photo: Flickr/Flickmor.

This is Serious Monkey Business is written by a recent undergraduate graduate looking to go onto grad school for primatology. In the meantime, she writes about whatever she can scrounge up on primatology and will be writing about her research experience with semi-captive lemurs in the near future. The writer can be found at Serious Monkey Business and she heavily recommends that readers explore more of Jason's work if they haven't already.