Abstract
The ability to reason about causality underlies key aspects of human cognition, but the extent to which non-humans understand causality is still largely unknown. The Aesop’s Fable paradigm, where objects are inserted into water-filled tubes to obtain out-of-reach rewards, has been used to test casual reasoning in birds and children. However, success on these tasks may be influenced by other factors, specifically, object preferences present prior to testing or arising during pre-test stone-dropping training. Here, we assessed this ‘object-bias’ hypothesis by giving New Caledonian crows and 5–10 year old children two object-choice Aesop’s Fable experiments: sinking vs. floating objects, and solid vs. hollow objects. Before each test, we assessed subjects’ object preferences and/or trained them to prefer the alternative object. Both crows and children showed pre-test object preferences, suggesting that birds in previous Aesop’s Fable studies may also have had initial preferences for objects that proved to be functional on test. After training to prefer the non-functional object, crows, but not children, performed more poorly on these two object-choice Aesop’s Fable tasks than subjects in previous studies. Crows dropped the non-functional objects into the tube on their first trials, indicating that, unlike many children, they do not appear to have an a priori understanding of water displacement. Alternatively, issues with inhibition could explain their performance. The crows did, however, learn to solve the tasks over time. We tested crows further to determine whether their eventual success was based on learning about the functional properties of the objects, or associating dropping the functional object with reward. Crows inserted significantly more rewarded, non-functional objects than non-rewarded, functional objects. These findings suggest that the ability of New Caledonian crows to produce performances rivaling those of young children on object-choice Aesop’s Fable tasks is partly due to pre-existing object preferences.
Highlights
Humans have exceptional causal reasoning abilities—the ability to understand relationships between cause and effect in the physical world—and some researchers have claimed that this type of sophisticated casual understanding is uniquely human in nature [1]
The Aesop’s Fable tasks generally involve the subject making a choice between two tubes or two different object types which can be inserted into one water-filled tube
Subjects in the present study were trained to select the non-preferred, non-functional objects: the floating objects and hollow objects before completing two Aesop’s Fable waterfilled tube experiments, in which they had the choice of inserting sinking vs. floating objects in Experiment 1A and solid vs. hollow objects in Experiment 1B
Summary
Humans have exceptional causal reasoning abilities—the ability to understand relationships between cause and effect in the physical world—and some researchers have claimed that this type of sophisticated casual understanding is uniquely human in nature [1]. The Aesop’s Fable paradigm involves dropping objects into partially water-filled tubes to bring a floating food reward within reach. This paradigm, alongside various other tool-use related tasks, has been used to explore what animals and children understand about the functional properties of objects, including their size, weight and solidity, and their relation to water displacement, tube size and water level (see [11, 12] for reviews of previous Aesop’s Fable studies). If the subjects significantly select the functional over non- or less functional tube or object, this has been taken to indicate that they may possess a causal understanding of object and substrate properties
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