Many times, I’ve been asked by family and friends what exactly it is that I do when I am working with the monkeys. Generally, I respond that I show the monkeys something and then see how they respond. While this is technically true, it is not very specific.

While my research falls into a lot of different categories (developmental psychology, comparative cognition, social cognition, etc.), put simply, I am really interested in what monkeys know about what others know or can see. This ability is called ‘theory of mind’, and it refers to the way that we are able to think about other people’s perceptions, emotional states, beliefs, knowledge (or ignorance), desires, and perspectives [1]. Humans do this every day, all the time. We can think about what other people are thinking when we are talking with them and when we are talking about them, when we are thinking about them, looking at them, etc. If you are chatting with someone and then suddenly they begin to frown, you might infer that something you said made them sad. Similarly, if you are talking with someone and suddenly their gaze shifts to something behind you, you will likely turn around (an aside: this latter ability is called ‘gaze following’ and is so cool that I hope to cover it separately at some point, more on gaze following later..)

Anyways, after decades of work by my adviser and some of her past students, we generally believe that rhesus monkeys, while able to do visual [2] and auditory [3] perspective taking, are not doing ‘theory of mind’ the same way that humans are (the details of this are complicated, but if you are interested, see [4]). Put simply, it does not seem like rhesus macaques can represent events that differ from the current state of the world. A quick example might make this more clear.

Imagine that you are sitting in a room with two of your family members — your mom and sibling. Your mom is cleaning, and your sibling is reading a book, but then gets up to grab something from the other room and leaves the book on the coffee table. While they are gone, you mom accidentally puts the book back on the shelf. When your sibling comes back, where do you think they would look for the book?

For us, this should be easy to figure out: your sibling left the book on the coffee table, so they should look for the book on the table because they didn’t know that your mom moved the book to the shelf since they were out of the room. Even a more simplified version of this task is not so simple for a monkey. In an experiment from 2011, they failed to form expectations about where the person should look for the hidden object [5].

However, as aforementioned, rhesus macaques do seem capable of using another person’s visual perspective. Further, they can use this visual perspective to form an expectation about where the person should search for an object [5]. Because recent studies in different species of macaques show differences in their social cognition [6], I am interested in whether Barbary macaques will form expectations about how a person should act (like rhesus macaques), or will show a different pattern of behavior.

To do this, I sit about a meter away from the Barbary macaques (see the first picture above) and show them a series of actions on a stage. A second person sits directly behind me and films a close-up video of the monkey’s face.

Later, we remove all of the information relevant to the study, and have someone who is blind to the study hypothesis watch all the videos back and code when they think the monkey is looking at the experimental setup. Finally, we compare average looking in the different experimental conditions to see whether or not Barbary macaques generally expect people to act consistently with their visual perspectives.

I will keep you updated with the results with the study as soon as I know, but this can sometimes take months! Let me know in the comments (or contact me directly) if you have any other questions or want to know more about anything I wrote about here. Thanks for following along so far and I hope to update you again soon.

 

REFERENCES

[1] Frith, C., & Frith, U. (2005). Theory of mind. Current Biology, 15(17), R644-R645.

[2] Flombaum, J. I., & Santos, L. R. (2005). Rhesus monkeys attribute perceptions to others. Current Biology, 15(5), 447-452.

[3] Santos, L. R., Nissen, A. G., & Ferrugia, J. A. (2006). Rhesus monkeys, Macaca mulatta, know what others can and cannot hear. Animal Behaviour, 71(5), 1175-1181.

[4] Martin, A., & Santos, L. R. (2016). What cognitive representations support primate theory of mind?. Trends in Cognitive Sciences, 20(5), 375-382.

[5] Marticorena, D. C., Ruiz, A. M., Mukerji, C., Goddu, A., & Santos, L. R. (2011). Monkeys represent others’ knowledge but not their beliefs. Developmental Science, 14(6), 1406-1416.

[6] Rosati, A. G., & Santos, L. R. (2017). Tolerant Barbary macaques maintain juvenile levels of social attention in old age, but despotic rhesus macaques do not. Animal Behaviour, 130, 199-207.