Chimpanzees show some evidence of selectively acquiring information by using tools, making inferences, and evaluating possible outcomes

Abstract

Metacognition refers to thinking about one's thinking or knowing what one knows. Research suggests that this ability is not unique to humans and may be shared with nonhuman animals. In particular, great apes have shown behaviors on a variety of tasks that are suggestive of metacognitive ability. Here we combine a metacognitive task, the information-seeking task, with tool use and variable forms of initial information provided to chimpanzees to explore how informational states impact behavioral responses in these apes. Three chimpanzees were presented with an apparatus that contained five locations where food could be hidden. If they pointed to the correct location, they received the reward, but otherwise they did not. We first replicated several existing findings using this method, and then tested novel hypotheses. The chimpanzees were given different types of information across the experiments. Sometimes, they were shown the location of the food reward. Other times, they were shown only one empty location, which was not useful information. The chimpanzees also could use a tool to search any of those locations before making a selection. Chimpanzees typically used the tool to search out the location of the reward when they could not already know where it was, but they did not use the tool when they already had been given that information. One chimpanzee made inferences about the location of hidden food, even when that food was never shown in that location. The final experiment involved hiding foods of differing preference values, and then presenting the chimpanzees with different initial knowledge states (i.e., where the best food was located, where the less-preferred food was located, or where no food was located). All chimpanzees used the tool when they needed to use it to find the best possible item on that trial, but responded by choosing a location immediately when they did not need the tool. This finding highlights that their behavior was not the result of a simple rule following such as pointing to where any food had been seen.

Fig 1. The apparatus.

The top left panel shows the chimpanzee’s view of the apparatus when the blind was lowered. The top right panel shows the view when the blind was raised, and the five containers could be seen. Each was covered with a uniquely-colored cover and attached clear lid. Each lid could be raised or lowered using the tool as in the bottom panel. In some cases, as in the top right panel, more than one container could be revealed simultaneously for the chimpanzee to view whether food was hidden in that container or not.

Fig 2. Tool use in Experiment 2.

The percentage of trials each chimpanzee used the tool to inspect containers in each condition and for each half of Experiment 2. None of the chimpanzees showed statistically significant differences in use of the tool in the first half of the experiment, but all did so in the second half.

Fig 3. Tool use in Experiment 3.

The percentage of trials each chimpanzee used the tool to inspect containers in each condition in Experiment 3. A pattern indicative of inferential reasoning would be apparent if use of the tool in the inference reveal condition was as low as the food reveal condition, versus the expected high use of the tool in the empty reveal condition. Only Sherman showed this pattern indicative of inferential reasoning.

Fig 4. Tool use in Experiment 5.

The percentage of trials on which each chimpanzee used the tool to inspect containers in each of the five test conditions in Experiment 5. The two lightest colored bars are trial types in which one would expect little or no use of the tool given that all information about where the best item on that trial was located was already provided. For the three darkest bars, the chimpanzees could not know where the best food item on that trial was located without using the tool.