Daniel Horschler, 2020 Gruener Research Travel Awardee
Daniel Horschler
Ph.D. Student
Cognitive Science GIDP
Research Location
Humacao, Puerto Rico
On Site Research Dates
May 15, 2020 - June 14, 2020
Title of Research Project:
"Do Monkeys Truly Represent Others' True Beliefs?"
Project Summary
Whether, and to what extent, animals understand the mental states of others is a longstanding question in comparative cognition. As adult humans, we recognize that other agents act in ways that are consistent with the facts they have about the world. We understand that others know things and we use these cognitive representations of others’ knowledge to make predictions about how individuals will behave. This project aims to assess whether monkeys, like humans, can represent others’ knowledge (i.e. true beliefs) about the world. My first study in this line of research offers support for the idea that monkeys do not represent others’ true beliefs like humans, but rather use a simple heuristic that results in systematic errors in their expectations about others’ knowledge in certain cases, and therefore helps to explain a host of seemingly contradictory results in the literature [1]. As a follow-up, my proposed study will more critically examine what specific factors cause these systematic errors. In other words, this study will help explain how and why monkeys do not represent others’ knowledge states in the same way that humans do.
Description of Research
The broad goal of this project is to better understand which aspects of our human theory of mind (which enables us to understand that others have desires, knowledge, and beliefs that can be different from our own) are unique to our species and which aspects are shared with other primates. Previous research has demonstrated that monkeys behave as if they have an understanding of others’ knowledge states based on events that others have seen in the past, but are unable to understand that others can have beliefs about the world that are not objectively true [2,3]. This puzzling pattern has led researchers to hypothesize that monkeys understand others’ knowledge in a fundamentally different way than humans do [4]. My previous work offers the first explicit support of this awareness relations hypothesis [1], and my proposed project will extend this research by examining the specific mechanisms behind how monkeys predict the ways in which knowledgeable agents will act.
In my previous work [1], monkeys watched as an agent saw a piece of fruit being hidden in one of two boxes. Next, while the agent’s view of the boxes was blocked, the fruit was either moved out of and back into the same box, or the box itself flipped open and closed briefly. The agent then reached into either the correct or incorrect box to search for the fruit. Using an expectancy violation measure as in previous studies (in which subjects are expected to look longer at events that they do not predict or are surprised by), monkeys looked longer at the agent’s incorrect as compared to correct reach in conditions where the box moved but not conditions where the fruit moved. This result indicated that monkeys expected the agent to have knowledge of the fruit’s location and to reach correctly when the box moved, but not when the fruit moved. In other words, monkeys’ understanding of the agent’s knowledge of the fruit’s location was disrupted simply because the fruit was arbitrarily moved while the agent could not see it. Even though the agent just saw where the fruit was hidden, and it always ended up in that same place across conditions, monkeys did not expect the agent to have knowledge about it in some cases.
As a follow-up, I have collected currently unpublished data showing that monkeys’ understanding of others’ knowledge is similarly disrupted when a hidden object changes sizes while an agent cannot see it, but not when the object changes colors. However, to publish these data, I need to run additional control conditions to show that monkeys sufficiently attend to and recognize these size and color changes. Therefore, any funds I receive from this award will be used for travel to and from my field site to collect these data in March 2020. These control conditions will use a habituation/dishabituation paradigm to demonstrate that monkeys are sensitive to both object manipulations. First, monkeys will watch as an agent opens a box to reveal an object for two consecutive trials of 10 seconds each. On a third trial, the agent will open the box to reveal either the same object, or a manipulated version of the object (i.e. that has changed in either size or color) in a between-subjects design. If monkeys are sensitive to these manipulations, they should look longer on third trials when the object changes as compared to when it stays the same. If monkeys are sensitive to these object changes as expected, I will submit a new paper demonstrating that monkeys’ understanding of others’ knowledge is disrupted by changes to an object’s size (similar to arbitrary object movements as in [1]) but not an object’s color. Collectively, this work argues that monkeys do not represent others’ true beliefs about objects in the same way as humans.
Data Collection Plan
I will test free-ranging rhesus macaques living on the island of Cayo Santiago in Puerto Rico. Consistent with previous work [1–3], I plan to test roughly 200 monkeys. To attain a sufficient sample size to detect statistically significant differences in both experiments (i.e. changes to an object’s size versus color), I will test 100 monkeys in each experiment. Within each experiment, 50 monkeys will see the same object across all three trials whereas 50 monkeys will see a manipulated version of the object on the third trial. My advisor and I will collaborate with Dr. Laurie Santos at Yale University on this project.
Career Impact
I am planning to use this work to contribute to my dissertation, focusing on how humans may possess unique representational and motivational socio-cognitive capacities that allow us to understand the richness of other minds. I hope to integrate this project and my previous work on theory of mind in monkeys with experiments I am currently collecting data for on dog-human cooperation. A potentially powerful explanation of the uniqueness of human cognition centers on a combination of our deep understanding of others’ mental states (which monkeys exhibit aspects of) along with our capacity and motivation to form cooperative joint experiences and goals with others (which dogs exhibit aspects of). Studying the origins of theory of mind in monkeys therefore has potential to shed new light on how the human mind evolved.
Publishing this work will also help to advance my line of research on the awareness relations hypothesis of primate theory of mind [4]. By building on my previously published empirical work in this area [1], this research will further support theoretical arguments I have proposed about how non-human primates conceptualize the minds of other animals [5].
References
1. Horschler DJ, Santos LR, MacLean EL. 2019 Do non-human primates really represent others’ ignorance? A test of the awareness relations hypothesis. Cognition 190, 72–80.
2. Marticorena DCW, Ruiz AM, Mukerji C, Goddu A, Santos LR. 2011 Monkeys represent others’ knowledge but not their beliefs. Dev. Sci. 4, 1406–1416.
3. Martin A, Santos LR. 2014 The origins of belief representation: Monkeys fail to automatically represent others’ beliefs. Cognition 130, 300–308.
4. Martin A, Santos LR. 2016 What Cognitive Representations Support Primate Theory of Mind? Trends Cogn. Sci. 20, 375–382.
5. Horschler DJ, Santos LR, MacLean EL. Submitted. Do non-human apes really represent others' beliefs?