The representational systems for object and agent in new world monkeys

Abstract

Representing the environment in its most basic components, namely objects and agents, is a fundamental feature of human cognition which we may share to different extents with nonhuman animals. This thesis explored some manifestations of these abilities in two new world monkey species, squirrel monkeys and capuchin monkeys.

We first investigated squirrel monkeys’ ability of individuating object by spatiotemporal and property/kind information with a “magic box” paradigm using both manual search and looking time measures (chapter 2). The squirrel monkeys failed both tasks with both measures, whereas capuchin monkeys showed individuating competence with exactly the same tasks and apparatus in a previous study.

Chapter 3 tested and explored the possibility that squirrel monkeys failed the “magic box” tasks that capuchin monkeys passed because they acted so fast that they didn’t form or use this type of object representations to guide their actions. In fact, in a touchscreen-based object tracking/catching game (Whack-a-cricket task), the squirrel monkeys were slower to “catch” a moving “cricket” compared to capuchin monkeys.

In chapter 4, we tested squirrel monkeys with another individuation task that included two separate barriers instead of a single box. The squirrel monkeys preferred to search the last- visited-location first when either spatiotemporal or property/kind information suggested that only one object was present. This preference disappeared when either information indicated that there were two objects, one behind each barrier. We conclude that squirrel monkeys are therefore able to individuate objects using both kinds of information when tested with an appropriate task.

In the last chapter, we investigated whether capuchin monkeys can locate a causal agent based on an event that he initiated from a hidden location. Capuchin monkeys located the hidden agent when they saw an object pushed, raked, rolled, or thrown across a table seemingly by the experimenter behind one of two screens (agentive trials), but not when they saw an object roll down a ramp or fall off a block after a shake of the table (arbitrary control trials) that contained no information about the agent’ location. This result suggests capuchin monkeys can use motion events to infer the location of a causal agent, an ability also demonstrated by human infants.

Taken together, our studies show that squirrel monkeys and capuchin monkeys have some core abilities to represent some of the fundamental properties of objects and agents, comparable to those demonstrated by human infants, which supports the core knowledge view that such representational systems may have a long evolutionary history and exist widely in primates.