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About nuts and abstract concepts

When it comes to opening nuts, capuchins know very well which features a stone must possess to be functional. Indeed, they use the experience acquired in nature with a variety of stones, to identify the functional features in tools they had never used before. And what about concept learning? Well, if properly trained, even capuchins are able to recognize abstract concepts of same/different between items, and use it to categorize new sets of stimuli.

The ability to understand similarities and analogies is a fundamental aspect of human cognition and humans are well known for their analogy-making capabilities. According to some authors non-human animals lack true analogical reasoning that involves the ability to figure out similarities between relations. However, it is possible that analogy-making did not emerge abruptly in our species, and that its precursors are present also in monkeys. To disentangle this issue, we explored the behavior of capuchin monkeys in tool using and matching-to-sample tasks requiring different levels of abstraction.

Tool use

Wild capuchin monkeys living in the dry forest habitat of Piauí, in Brazil, use hammers and anvils to open nuts. An experiment was designed to find out if capuchins’ stone selection was accidental, or based on the ability to identify the functional features of the tool. Monkeys were given artificial and natural stones differing in features such as friability, size and weight. In this experiment, capuchins always chose the functional tool on the basis of material and weight, even when weight could not be judged by sight. These results demonstrate that capuchins are able to use the experience acquired in nature with a variety of stones, to select among tools they have never encountered before, those with features that are functional features to open the nuts.

We investigated how capuchin monkeys solve tool problems in captivity. This kind of problem solving requires an evaluation of the tool length and of the tubes containing a reward. In particular, capuchins had to select the longest tool from different sets of sticks varying in length and in the shape or color of the handle. Our findings show that, when trained to concentrate on the functional feature (the length), some capuchins learnt to select the right stick, thus demonstrating the acquisition of a relational rule. The same experiment was carried out with chimpanzees, who solved the task applying a relational rule more quickly than capuchins.

Videos from Sabbatini et al 2012 Animal Cognition

Matching to sample

This study was aimed to the evaluation of the capacity of capuchin monkeys to acquire abstract concepts of same/difference and use them to solve matching-to-sample (MTS) tasks, involving relations of an increasing level of abstraction. Capuchins were first trained to recognize the relation (either same or different) between two sample items. Then, they were tested in selecting, between two pairs of new items, those with the same relation of the sample stimuli. Moreover, we examined the ability of capuchins to solve this kind of relational MTS task on the basis of the number of items composing the stimuli. We found that under specific training conditions (i.e. the number and the kind of stimuli used during the training), capuchins accurately match novel stimuli, showing in this way the first evidence of same/different relational matching-to-sample abilities in a New World monkey. 

Videos from Truppa et al 2011 PlosOne

Researchers involved

Dr. Gloria Sabbatini, Dr. Valentina Truppa and Dr. Elisabetta Visalberghi


ico Bullet Scientific publications

ico Bullet Capuchins and media


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