Shape and texture biases in dogs' generalization of trained objects.

Shape bias, the tendency to link the meaning of words to the shape of objects, is a widely investigated phenomenon, but the extent to which it is linked to vocabulary acquisition and/or to tool using is controversial. Understanding how non-human animals generalize the properties of objects can provide insights into the evolutionary processes and cognitive mechanisms that influence this bias. We investigated object generalization in dogs, focusing on their tendency to attend to shape or texture in a two-way choice task. We analyzed data of thirty-five dogs that were successfully trained to discriminate a target object among distractors and retrieve it to their owner. In subsequent testing, dogs chose between objects similar to the target in either shape or texture. Results showed that dogs first approached objects of similar shape, but then predominantly chose objects of similar texture. This suggests a reliance on visual cues for initial assessment and tactile cues for final discrimination. Our findings highlight the influence of perceptual modalities on object generalization in dogs, showing that, before object manipulation, they seem to show a shape bias but, once they make physical contact with the objects, they rather rely on texture to generalize. This study contributes to our understanding of generalization in a non-verbal and non-tool using species and opens avenues for comparative investigations into the relationship between vocabulary acquisition, tool using and biases in object generalization.