Mirror, Mirror

1471836761_11edeb5212_mHumans use mirrors so easily that we often don’t think about the cognitive processes required to do so (although we do derive entertainment from those animals that just don’t “get” mirrors). Being able to recognize oneself in the mirror doesn’t seem like an evolutionarily advantageous skill, but scientists think that this ability may indicate the possession of other skills more relevant to survival.

For example, mirror self-recognition may be indicative of self-consciousness and, by extension, theory of mind (the ability to think about what others may be thinking); being self-conscious, or having knowledge of the self, may naturally lead to having knowledge of others. These skills are especially important for social animals, as theory of mind allows us to take the perspective of others, which is the basis for empathy. (Evidence for the connection between mirror self-recognition and theory of mind comes from studies with young children, which have found that mirror self-recognition and perspective-taking abilities develop at around the same time.)

But how can we tell whether animals and pre-linguistic children connect what they see in the mirror to their physical selves? The most commonly used measure is the Mirror Test (also called the Mark Test or the Rouge Test), which was developed by Gordon Gallup, Jr. in 1970. After a familiarization period with a mirror, a colored mark is placed on an area of an animal that can’t be seen without the use of a mirror (usually somewhere on the face). The animal is then exposed to a mirror again, and her behavior is closely monitored. If the animal touches the mark on her own face (rather than the mirror), then she has “passed” the Mirror Test and demonstrates mirror self-recognition.


Not quite there yet…

When first exposed to a mirror, most animals (including humans) exhibit social behaviors like lip smacking and attempts to play, indicating that they perceive their reflection as a conspecific. After some cognitive development and experience with mirrors, however, some animals will demonstrate mirror self-recognition (for humans, this occurs around 18-24 months of age).

Unsurprisingly, humans’ closest evolutionary relatives, the great apes, demonstrate mirror self-recognition (the great apes include chimpanzees, bonobos, gorillas, and orangutans; all have passed the Mirror Test). Additionally, some very distant relatives of humans, but who are also highly social and have demonstrated advanced cognitive abilities, have passed the Mirror Test: dolphins and elephants.

One unexpected species that has passed the Mirror Test is the magpie. But when you consider their other cognitive abilities, it’s not so surprising: magpies have also demonstrated the abilities of tool use, perspective-taking, and foresight. (Why would these abilities be particularly helpful to magpies? Researchers theorize that they enable magpies’ prolific thievery.)

7193567450_b7ebd10bb2_mInterestingly, lesser apes (gibbons) and monkeys fail the Mirror Test, suggesting that mirror self-recognition and all the attendant cognitive abilities (self-consciousness, perspective-taking, etc.) evolved after the evolutionary split between great and lesser apes (which occurred after the split between apes and monkeys). Elephants, dolphins, and magpies, then, must have evolved the abilities through convergent evolution.

So it seems pretty simple: pass the Mirror Test, and you demonstrate mirror self-recognition and its associated cognitive abilities. Yet, as with most matters in animal cognition, this one is far from cut-and-dry.

Some researchers have argued that the Mirror Test isn’t appropriate for many animals. First, a colored mark on the face may not be salient enough for some animals (it may not stand out or be important enough for the animals to notice). Additionally, just because an animal doesn’t touch or try to remove the mark doesn’t mean he doesn’t recognize his reflection; perhaps he notices the mark but just doesn’t care. Finally, what about animals who have poor vision, or who rely primarily on other senses? Surely we can’t say they lack the abilities of self-consciousness and perspective-taking simply because they don’t pass the Mirror Test.

This issue is complicated even when studying children: some studies have shown vast cultural differences in performance on the Mirror Test. For example, many of the Kenyan children in one study froze in response to seeing their reflections. While some of these cultural differences could be attributed to differences in experience with mirrors, researchers think they are likely more related to different parenting styles and differences in how the children understand the task. Children raised in cultures with a high emphasis on obedience, for example, may recognize their reflections but be unsure of whether they’re allowed to investigate or remove the mark.

1921632741_baee2c47b8_mThese criticisms of the Mirror Test have prompted some researchers to try to find other methods of gauging whether animals demonstrate mirror self-recognition. Some possible alternative indicators include mirror-guided self-directed behaviors (like using the mirror to examine one’s body) and the disappearance of social responses to the mirror. Some researchers attempted to use these indicators as proof that macaques can recognize themselves in the mirror, although their interpretation has been questioned. (I highly recommend reading these papers and judging for yourself – you can find the original paper here. Unfortunately, the rebuttal paper isn’t available for free, but the same authors briefly discuss their criticisms in this article.)

This brings me to a tangential point about scientific research in general. These kinds of exchanges regularly occur in science, regardless of the particular field. Often, one researcher (or a group of researchers) finds an issue with another researcher’s methods or conclusions. Sometimes she will just write a rebuttal pointing out the flaws she sees or offering an alternate interpretation of the results, but she may also conduct her own experiment, fixing any methodological flaws from the original study. While it is undoubtedly frustrating to have your methods and conclusions questioned, it ultimately leads to better science by pushing researchers to really think about and improve task design and to be very careful about interpreting results.

It is also the theoretical basis of how we disseminate findings in the scientific community: after careful consideration by other scientists in the field (peer review), we publish not only the conclusions of our experiments, but also our exact methods, our data, and the related prior research that helps lead us to those conclusions. In essence, we tell a story about our research. Others can then follow along and, rather than taking our word for it, decide for themselves whether our story is compelling and what makes it so (or not).

(As I said, though, this is all in theory. There is currently quite a bit of debate concerning how papers are chosen for journals, whether access to these papers should be free to everyone, and a host of other issues relating to publishing scientific research.)

174px-Mirror_test_with_a_BaboonBut I digress. Hopefully this was a thought-provoking summary of what mirror self-recognition can (but possibly can’t) tell us about certain cognitive abilities. I’ll leave you with this video about the Mirror Test in primates (starts at 1:00), and this one about dolphins and elephants.





Anderson, James R., and Gordon G. Gallup. “Do rhesus monkeys recognize themselves in mirrors?.” American journal of primatology 73.7 (2011): 603-606.

Anderson, James R., and Gordon G. Gallup Jr. “Which primates recognize themselves in mirrors?.” PLoS biology 9.3 (2011).

Broesch, Tanya, et al. “Cultural variations in children’s mirror self-recognition.” Journal of Cross-Cultural Psychology 42.6 (2011): 1018-1029.

de Waal, Frans BM. “The thief in the mirror.” PLoS biology 6.8 (2008).

Gallup, Gordon G. “Chimpanzees: self-recognition.” Science (1970).

Plotnik, Joshua M., Frans BM De Waal, and Diana Reiss. “Self-recognition in an Asian elephant.” Proceedings of the National Academy of Sciences 103.45 (2006): 17053-17057.

Prior, Helmut, Ariane Schwarz, and Onur Güntürkün. “Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition.” PLoS biology 6.8 (2008): e202.

Rajala, Abigail Z., et al. “Rhesus monkeys (Macaca mulatta) do recognize themselves in the mirror: implications for the evolution of self-recognition.” PLoS One 5.9 (2010): e12865.

Reiss, Diana, and Lori Marino. “Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence.” Proceedings of the National Academy of Sciences 98.10 (2001): 5937-5942.

Suddendorf, Thomas, and David L. Butler. “The nature of visual self-recognition.” Trends in cognitive sciences 17.3 (2013): 121-127.


Also interesting:

Platek, Steven M., and Sarah L. Levin. “Monkeys, mirrors, mark tests and minds.” Trends in ecology & evolution 19.8 (2004): 406-407.

Suddendorf, Thomas, and David L. Butler. “Response to Gallup et al.: are rich interpretations of visual self-recognition a bit too rich?.” Trends in cognitive sciences (2013).

The Monkey and the Snake

Last week’s post detailed evidence that two marine species, lemon sharks and damselfish, can learn socially, and also demonstrated that social learning can be used both to obtain food and avoid predators. In this post, I’d like to expand more on the latter, since a series of interesting research has been done on predator avoidance (or, more accurately in this case, predator fear) in monkeys.

237px-Rhesus_Macaques_-_croppedIt all began with a study by Joslin, Fletcher, & Emlen (1964) that compared the fear responses of wild-reared and lab-reared rhesus macaque monkeys to snakes. Presumably the wild-reared monkeys would have had previous experience with snakes, but the lab-reared monkeys would not. They found that only the wild-reared monkeys had a fear response to the snakes, indicating that the fear of snakes in rhesus monkeys is learned, rather than innate.


Cook & Mineka (and colleagues) picked up and greatly extended this line of research in the 1980s. They were interested in seeing whether this fear could be socially learned, so they exposed wild-reared monkeys to snakes while lab-reared monkeys watched. (Don’t worry – the snakes were behind plexiglass!) The lab-reared monkeys initially didn’t have a fear response to snakes, but after observing the responses of wild-reared monkeys to snakes, they exhibited a fear response. The lab-reared monkeys had socially learned to be afraid of snakes.

Interestingly, the degree of the fear response of the lab-reared monkeys was correlated with the degree of the fear response of the wild-reared demonstrator monkey observed. The greater the fear response of the demonstrator monkey, the greater the fear response of the monkey that observed him.  This indicates just how powerful social learning can be, if even the degree of the response can be transmitted!

320px-Banded_water_snake_in_AlabamaCook & Mineka next wanted to investigate whether extensive neutral prior experiences with snakes could affect whether lab-reared monkeys learned the fear of snakes. In the “immunization” condition, lab-reared monkeys observed the non-fearful responses of other lab-reared monkeys to snakes. In the “latent inhibition” condition, lab-reared monkeys were exposed to snakes for a long period of time (again, the snakes were behind plexiglass). Then both groups observed the responses of fearful monkeys to snakes. The monkeys in the latent inhibition group showed a fear response when exposed to snakes again. The immunization group, however, generally did not show a fear response to snakes (only 2 out of the 8 monkeys in this condition showed a fear response). This showed that while monkeys can socially learn to fear snakes, their initial lack of fear can also be reinforced by the non-fearful responses of other monkeys.

So far, these results agree with what we’ve already learned about social learning. But here’s where things get interesting. As I’ve mentioned before, we often study animal cognition with a view to learning more about human cognition. Cook & Mineka were interested in connecting their work on fear in monkeys to fear in humans, and specifically the very specific, intense fears we call phobias. They noted that most phobias are of things that have existed for thousands of years (like heights and, yes, snakes). However, there aren’t any phobias of more recently invented dangers (like guns). This suggests that there may be a role of evolution in the development of phobias.

In this vein, Cook & Mineka wondered if fear of anything (whether dangerous or not) could be socially learned, or if, similar to phobias, the monkeys were evolutionally predisposed to fear only certain things.

284px-Macaque_India_4To investigate this, the researchers tried to teach monkeys to be afraid of flowers. This required a little movie magic: instead of having naïve monkeys observe the responses of actual fearful monkeys, they showed them a video of a monkey reacting fearfully to a stimulus. (The researchers first verified that watching the video was just as effective at socially teaching fear as watching the actual fearful monkey.) By using video, they could manipulate the demonstrator’s response so it looked like the monkey was responding fearfully to a flower (when, in reality, it was responding fearfully to a snake). The researcher showed one group of monkeys a video of a monkey responding fearfully to a flower but not to a snake, and showed the other group a video of a monkey responding fearfully to a snake but not a flower (importantly, the responses of the monkey in the videos were exactly the same – the only difference was what it was responding to).

They found that the monkeys in the latter group, which saw the monkey respond fearfully to the snake but not the flower, developed a fear of snakes (as we would expect). However, the other group, which saw the monkey respond fearfully to the flower but not the snake, did not develop a fear of flowers or snakes. This experiment was repeated using a toy crocodile in place of a snake and a stuffed rabbit in place of a flower, with the same results. These results indicate that monkeys are evolutionally predisposed to fear certain things, but not others. They further suggest that only those fears that monkeys are predisposed to can be learned socially.

Cook & Mineka suggest a couple mechanisms for how this predisposition could work. It could be that monkeys have evolved a predisposition to fear very specific things: they have the general concept of a snake somehow stored in their brains and passed down through genes that predisposes them to fear snakes specifically. On the other hand, they could just have an instinctual knowledge of the features that make things dangerous, like sharp teeth (remember the Halloween mask study?)

320px-Coast_Garter_SnakeInterestingly, there is actually a theory (called the Snake Detection Theory) that suggests that the complex visual systems of primates developed for the purpose of detecting snakes so as to avoid them. (It also suggests that pointing developed in order to allow us to warn others about snakes.)


Also, in a fascinating connection to neuroscience, researchers recently discovered neurons in the pulvinar area of the brain (involved in redirection of attention and motor responses to threats) that respond quicker and more strongly to images of snakes than images of monkeys or geometric shapes. What might this result suggest about the mechanism for a predisposition to fear snakes?

Sources Cited:

Cook, Michael, and Susan Mineka. “Observational conditioning of fear to fear-relevant versus fear-irrelevant stimuli in rhesus monkeys.” Journal of Abnormal Psychology 98.4 (1989): 448.

Cook, Michael, and Susan Mineka. “Selective associations in the observational conditioning of fear in rhesus monkeys.” Journal of Experimental Psychology: Animal Behavior Processes 16.4 (1990): 372.

Cook, Michael, et al. “Observational conditioning of snake fear in unrelated rhesus monkeys.” Journal of abnormal psychology 94.4 (1985): 591

Isbell, Lynne A. The fruit, the tree, and the serpent: why we see so well. Harvard University Press, 2009.

Joslin, J., H. Fletcher, and J. Emlen. “A comparison of the responses to snakes of lab-and wild-reared rhesus monkeys.” Animal Behaviour 12.2 (1964): 348-352.

Mineka, Susan, et al. “Observational conditioning of snake fear in rhesus monkeys.” Journal of abnormal psychology 93.4 (1984): 355.

Mineka, Susan, Richard Keir, and Veda Price. “Fear of snakes in wild-and laboratory-reared rhesus monkeys (Macaca mulatta).” Animal Learning & Behavior 8.4 (1980): 653-663.

Mineka, Susan, and Michael Cook. “Immunization against the observational conditioning of snake fear in rhesus monkeys.” Journal of Abnormal Psychology 95.4 (1986): 307.

Van Le, Quan, et al. “Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes.” Proceedings of the National Academy of Sciences 110.47 (2013): 19000-19005.

Experience or Evolution?

Last week’s post talked about how dogs can use human social cues like pointing to find hidden food, and that chimps, though more closely related to humans evolutionarily, cannot. How do we explain this?

3517862378_43be39f2f6_mA major difference between dogs and chimps that could explain their difference in this skill is that dogs just have more experience with humans than chimps do. All the dogs tested on their use of human social cues had interacted with humans since birth. The chimps, though they had exposure to the humans who took care of them in the sanctuary where they lived, arguably had much less interaction with humans than the dogs. So, the factor influencing performance on the food-finding task (and understanding of human social cues) could be the amount of experience an animal has with humans. This theory is called the “human exposure hypothesis”.

One way to evaluate this theory is to test very young puppies on the food-finding task. The puppies, due to their young age, would necessarily have less experience interacting with humans. If the human exposure hypothesis is true, we would expect the puppies’ performance on the task to be worse than older dogs’ performance.

When researchers tested puppies between 9 and 24 weeks of age, they found that they were also able to understand human social cues. Moreover, age (i.e. amount of experience with humans) was not correlated with performance on the task — younger puppies were just as good at the task as older puppies. These findings indicate that the human exposure hypothesis is incorrect, and suggests that the ability to understand human social cues is innate in dogs.

5532096313_cfaf563c7a_mAnother possible explanation for the ability of dogs to understand human social cues when chimps cannot is that dogs have been domesticated — they’ve been selectively bred to have characteristics desirable to humans. We don’t know the specific details of how dogs were domesticated, but we do know that they split from their ancestors, gray wolves, about 100,000 years ago.

Researchers tested wolves on the food-finding task and found that they were unable to use human social cues to find the food, indicating that dogs acquired this ability sometime after their split with wolves. This finding supports the theory that dogs evolved the ability to understand human social cues through domestication (this theory is called the “domestication hypothesis”).

So, unlike chimps, it seems that dogs are able to understand human social cues because they’ve been bred by humans to do so. But a couple questions remain:

1. Was the evolution of this skill due to humans specifically breeding wolves that understood human social cues, or was it due to humans breeding wolves based on a more general trait, like behaving friendly towards humans (or, on the other hand, NOT breeding wolves that showed aggression towards humans)?

2. How would you even test the domestication hypothesis, besides spending thousands of years selectively breeding wolves (again)?

Next week’s post will explore the answers to these questions and conclude this series on dogs and human social cues!

Until then, here’s an interesting video that talks a bit about how dogs evolved from wolves and suggests that dogs played an important part in human evolution.


Hare et al. (2002) presents data from both the studies mentioned above, and also briefly discusses a few hypotheses of why dogs can understand human social cues.

Hare, Brian, et al. “The domestication of social cognition in dogs.” Science 298.5598 (2002): 1634-1636.