The case of the magic bones: Dogs’ memory of the physical properties of objects

Dogs’ memory for properties of occluded objects was assessed using a looking-time procedure. The looking-time procedure has been used to indicate that a change in expectation has been observed, with longer looking times associated with change as compared with no change. In our experiments, a bone-shaped dog biscuit (bone) was placed behind a horizontal screen that then rotated up to occlude the object before the screen returned to its horizontal position. Dogs were shown one of two test events. In one (congruent) event, the screen rotated up to obscure the bone and then rotated back down to reveal the unchanged bone. In the other (incongruent) event, the screen rotated up to obscure the bone and then rotated back down to reveal a bone that had changed in size (Experiment 1) or color (Experiment 2). Looking times were measured to assess which events represented the detection of a change. Increased looking time on incongruent trials indicated that the dogs remembered the size and color of the occluded object.