What kind of information animals use when solving problems is a controversial topic. Previous research suggests that, in some situations, great apes prefer to use causally relevant cues over arbitrary ones. To further examine to what extent great apes are able to use information about causal relations, we presented three different puzzle box problems to the four nonhuman great ape species. Of primary interest here was a comparison between one group of apes that received visual access to the functional mechanisms of the puzzle boxes and one group that did not. Apes’ performance in the first two, less complex puzzle boxes revealed that they are able to solve such problems by means of trial-and-error learning, requiring no information about the causal structure of the problem. However, visual inspection of the functional mechanisms of the puzzle boxes reduced the amount of time needed to solve the problems. In the case of the most complex problem, which required the use of a crank, visual feedback about what happened when the handle of the crank was turned was necessary for the apes to solve the task. Once the solution was acquired, however, visual feedback was no longer required. We conclude that visual feedback about the consequences of their actions helps great apes to solve complex problems. As the crank task matches the basic requirements of vertical string pulling in birds, the present results are discussed in light of recent findings with corvids.
Problem solving Causal cognition Puzzle box Perceptual-motor feedback
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Christoph Völter was supported by a German National Academic Foundation studentship. We thank Raik Pieszek for constructing the experimental apparatuses and the animal caretakers of the Leipzig Zoo. We also thank Matthias Allritz, Virginia Gonzalez, and Carolin Kade for their help with data collection.
Conflict of interest
The authors declare that they have no conflict of interest.
Online Resource 1 Crank apparatus: phase I, crank-blocked condition. Video clip shows the first trial of the bonobo Kuno. At the beginning of the trial the reward-screen was released which covered the reward in its starting position. Kuno reached the reward after 142 seconds (MPG 27854 kb)
Online Resource 2 Crank apparatus: phase II, opaque condition. Video clip shows the first trial of the bonobo Kuno (after having solved the problem three times before in the crank-blocked condition). At the beginning of the trial the reward- and progress-screen were released. The subject could not see the reward and its progress while turning the handle of the crank. Kuno reached the reward after 29 seconds (MPG 7267 kb)
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