Searching high and low: Domestic dogs’ understanding of solidity

Abstract

Physical reasoning appears central to understanding how the world works, suggesting adaptive function across the animal kingdom. However, conclusive evidence for inferential reasoning about physical objects is limited to primates. We systematically tested a central feature—understanding of solidity—in domestic dogs, by adapting a validated procedure (the shelf task) previously used to test children and non-human primates. Dogs watched a treat dropped into an apparatus with a shelf either present (treat landing on the shelf) or absent (treat landing on the bottom surface) and chose where to search for it (above or below the shelf). Across four studies (N=64), we manipulated visual access to the trajectory of the treat and apparatus interior. Dogs showed a high level of accuracy after 12 trials when the shelf was present (Study 1), even when visual cues of continuity were eliminated (Study 2), and when the shelf was absent (Study 3). As with toddlers, fully occluding the apparatus and alternating the presence and absence of the shelf within subjects showed at-chance performance in dogs (Study 4). The findings of these four studies suggest that dogs may be able to make inferences using solidity and continuity and do not exhibit proximity or gravity biases. However, dogs failed to search correctly when the rewarded location varied within-subjects, suggesting possible limits to their ability to make inferences about physical objects. We discuss physical inferences in dogs in the context of ecological and evolutionary affordances, and its role in making sense of the physical world.