Comparing the performances of apes (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus) and human children (Homo sapiens) in the floating peanut task

Abstract

Recently, Mendes et al. [1] described the use of a liquid tool (water) in captive orangutans. Here, we tested chimpanzees and gorillas for the first time with the same "floating peanut task." None of the subjects solved the task. In order to better understand the cognitive demands of the task, we further tested other populations of chimpanzees and orangutans with the variation of the peanut initially floating or not. Twenty percent of the chimpanzees but none of the orangutans were successful. Additional controls revealed that successful subjects added water only if it was necessary to obtain the nut. Another experiment was conducted to investigate the reason for the differences in performance between the unsuccessful (Experiment 1) and the successful (Experiment 2) chimpanzee populations. We found suggestive evidence for the view that functional fixedness might have impaired the chimpanzees' strategies in the first experiment. Finally, we tested how human children of different age classes perform in an analogous experimental setting. Within the oldest group (8 years), 58 percent of the children solved the problem, whereas in the youngest group (4 years), only 8 percent were able to find the solution.

Figure 1. Schematic illustration of the procedure used in Experiment 1and 2.

Figure 2. Spitting behavior for each of the three control conditions in Experiment 2.

2a) Mean number of trials in which subjects spat into the tube; 2b) Mean number of water spits that subjects added in total. * p<.05. Error bars depict the standard errors of the means.

Figure 3. Mean spitting rate for each group  =  Sum of the individual spitting rates divided by number of subjects in each group.

(a): 19 subjects from Leipzig tested with the new dispenser absent, (b): 25 subjects from Ngamba tested with the new dispenser present. (c): 16 subjects from (a) plus 3 new subjects from Leipzig tested with the new dispenser present.

Figure 4. Number of successful children for each of the three age classes.

Grey bars represent participants in the dry-condition group; black bars represent participants in the wet-condition group. * p<.05.