Research at CapLab


The Comparative Cognition Laboratory investigates the evolutionary origins of human cognition.  Our work aims to discover the foundational abilities that give rise to the complex cognitive capacities that are universally shared among human adults.  To do so, we study the cognitive capacities present in our species’ closest living phylogenetic relatives, the non-human primates (hereafter, primates).  Our work with primates takes a broadly comparative approach, comparing the cognitive abilities of a wide range of different species within the primate order, including five lemur species (ring-tailed lemurs, bamboo lemurs, mongoose lemurs, red-ruffed lemurs, and brown lemurs), capuchin monkeys, and rhesus macaques.



We perform our studies at three different research sites:


            • Capuchin Cognition Laboratory at Yale University


            • Cayo Santiago Field Station


            • Lemur Conservation Foundation Myakka City Reserve



Over the past few years, we have investigated a number of topics in the field of comparative cognition, using both field-based and laboratory-based behavioral studies.  The following projects provide an illustrative (though non-exhaustive) sample of the research questions that our lab has pursued over the past several years:



Primates’ Knowledge of Objects and Object Motion


Over the past few decades, developmental psychologists have learned a great deal about the core abilities that human infants use to represent objects and their motions.  Less is known, however, about whether infants’ core object reasoning capacities are shared more broadly with our close evolutionary relatives. Our lab has explored whether primates, like human infants, make accurate predictions about objects and the way they behave.  Our work has revealed that primates seem to represent objects in much the same way as human infants. We have shown that adult primates recognize that objects continue to exist when occluded (e.g., Santos, Barnes, and Mahajan, 2005), trace continuous paths in space and time (e.g., Santos, 2004), and retain their boundaries across motion (Santos, Barnes, Mahajan, and Blanco, under review).  Our work with primates has thus begun to suggest that our primate relatives may reason about physical objects in much the same way as human infants; specifically, primates may also represent objects in terms of Spelke’s principles of continuity, cohesion, and solidity (Santos, 2004). Interestingly, although primates seem to understand these object principles when tested in expectancy violation looking tasks, they seem unable to use these principles to make predictions about object motion when searching for food (see Santos, 2004 for review).  Our approach— which compares across species, across tasks, and across development— hopes to yield a more thorough understanding of the principles governing physical knowledge across development and evolution.



Domain-Specific Knowledge of Objects


A second line of research examines how primates spontaneously categorize the objects that make up their world.  Researchers have proposed that humans come to learn about different kinds of objects through the aid of domain-specific learning mechanisms, capacities that guide young learners to focus their attention to conceptually relevant perceptual inputs during early learning. Our lab has examined whether closely related primates share these domain-specific categorization biases. In particular, we have examined whether primates, like humans, recognize that different perceptual features are relevant for categorizing different kinds of objects. To do so, we have systematically contrasted primates’ knowledge of three different domains of objects— foods (Santos et al., 2001; Phillips and Santos, 2006), animals (Newman, Phillips. and Santos, under revision; Santos, Barnes, & Mahajan, in preparation), and tools (Santos, Mahajan, & Barnes, 2005; Santos et al., 2006)— with the developing knowledge that children possess about these domains.  Our most recent work in this area has begun to examine whether monkeys, like children, reason about different kinds of object in terms of their underlying, unseen essences.  This most recent work has discovered that rhesus monkeys possess some essentialist notions, such as an attention to an object’s unseen inside properties (Phillips and Santos, 2006),) and the capacity to track kind information across radical transformations (Shankar, Phillips, and Santos, in preparation).




Primate Social Cognition and Theory of Mind


One of the hallmarks of human cognition is our species' ability to reason about the minds of other individuals, a capacity commonly referred to as a theory of mind (ToM).  To date, there is still much controversy surrounding the question of whether primates share our mind-reading mechanisms.  Over the past few years, however, researchers have begun taking a new approach to the study of primate ToM, developing more ecologically-relevant competitive methodologies for testing primate mind reading. Our lab has begun using these new tasks to explore how lemurs and monkeys reason about others’ minds.  This work has revealed that monkeys (and sometimes lemurs) recognize what other individuals can and cannot see (Flombaum and Santos, 2005), what they hear and do not hear (Santos, Nissen, & Ferrugia, 2006), and possibly what they know and do not know.  Our current work is focused on the question of why primates fail to reveal this understanding in other non-competitive contexts (see Lyon and Santos, 2006 for review). 




An Evolutionary Approach to Social Decision-Making


Our most recent line of work has begun examining the nature of primate judgment and decision-making.  One of the most important insights in psychological science is the idea that human social cognition emerges from the operation of unconscious biases and heuristics.  Unfortunately, relatively little work has been devoted to the question of where these biases come from in the first place. In order to explore these problems, my colleagues and I have begun examining whether primates, who lack human unique experiences, share our species’ decision-making biases.  To this end, we have developed a token-trading task in which we are able to present captive capuchin monkeys with different economic and social problems. Using this set-up, we have demonstrated that capuchin monkeys evaluate economic decisions using reference points and prefer to avoid outcomes that are framed as losses, two classic hallmarks of human decision-making (Chen et al. 2006).  Future work now hopes to examine a broader range of social biases (e.g., judgment bias, ingroup/outgroup bias, etc.) and will explore the extent to which primate biases result from domain-specific mechanisms— whether they, like theory of mind mechanisms, operate more efficiently in ecological contexts involving competition among intentional agents.