To see or not to see: Horses’ ability to find the hidden treat

In animal cognition, the acquisition of object permanence is critical in many species to apprehend the physical world, including the position of conspecifics, alimentary resources or potential dangers. If most of the “highly cognitive” species, including great apes and some birds were shown to reach stage 6 (retrieving an object hidden invisibly at a new location) of Piagetian development, the ability of other species to reach stage 4 (retrieve an object entirely hidden) is more at stake. Domestic horses are exposed to a highly partitioned environment, and being able to mentally figure out the presence of a hidden object represents a particularly relevant challenge. In this study, we used a simple Piagetian-like task to determine whether horses would be able to retrieve a hidden treat when the displacement was not visible. Sixty-three horses, distributed amongst three groups, were tested. The Experimental (E) and first control (C1) horses were familiarised with the task of searching for the treat (a carrot) hidden under an upside-down bucket. During the test procedure, a carrot was placed under the bucket for E horses, but not for C1 horses. The second control group (C2) did not follow the familiarisation procedure and was presented with the upside-down bucket only to test a potential intrinsic effect of the bucket for exploration. In the groups that followed the familiarisation procedure, the success rate achieved 93.1 % (E group, the horses exposed and ate the treat) and 100 % (C1 group, the horses pushed the bucket enough to uncover the location of the theoretical position of the treat) which was significantly above chance (p < 0.001in both cases). In the C2 group, only 60.0 % of the horses touched and/or pushed the bucket, which was not above chance (p = 0.303) Our results show that horses are able to locate and find a hidden treat, even when the displacement was performed out of their sight, suggesting that they can at least reach Piaget’s stage 4 of object permanence task.