Sample video of a tamarin subject from experiment 1. The experimenter covered two containers with an opaque screen, lowered a raisin behind the middle of the screen, removed the screen, and then performed an action toward one of the containers. She then pushed the apparatus forward, allowing the subject to inspect one of the containers. This example depicts an intentional hand grasp action.
Sample video from the rhesus subject’s point of view for experiment 1. The experimenter placed two wooden platforms containing two potential food sources (half coconut shells turned upside down) on the ground in front of the subject, 2 meters apart and 2-5 meters from the test subject. The experimenter then looked at and performed the designated action toward one of the two coconuts, maintaining contact for 5 s. He then stood up, turned 180 degrees, and walked away at an even pace, allowing the monkey to approach and inspect one of the coconuts. This example depicts an intentional hand grasp action.
Sample video of a chimpanzee subject from experiment 1. The experimenter covered two containers with an opaque screen, and then lowered a food item behind the middle of the screen. Once the food was lowered behind the screen it was placed into the container that would later be the target of the experimenter’s action. The experimenter then removed the screen, separated the two containers by moving them to opposite ends of the table, and then performed the designated action toward one of the containers. He then moved the table forward so that the containers were within the subject’s reach; the subject indicated a choice by reaching through the cage wiring in the test room to contact the container. The subject was given the food item when the container targeted by the experimenter’s action was touched; if the subject touched the non-baited container, the baited container was withdrawn and the food item shown inside. This example depicts an intentional hand grasp action.