Dogs were tested for object permanence using an invisible displacement in which an object was hidden in one of two containers at either end of a beam and the beam was rotated. Consistent with earlier research, when the beam was rotated 180°, the dogs failed to find the object. However, when the beam was rotated only 90°, they were successful. Furthermore, when the dogs were led either 90° or 180° around the apparatus, they were also successful. In a control condition, when the dogs could not see the direction of the 90° rotation, they failed to find the object. The results suggest that the 180° rotation may produce an interfering context that can be reduced by rotating the apparatus only 90° or by changing the dogs' perspective. Once the conflict is eliminated, dogs show evidence of object permanence that includes invisibly displaced objects.
By the age of 2 years, children develop the ability to search for objects that have disappeared from view. According to Piaget (1954), these search behaviors result from a developing knowledge about the nature of objects in the environment. Piaget called this ability object permanence and assessed it using both visible and invisible displacement tasks.
In a visible displacement task, an experimenter places a desired object inside one of several identical opaque containers (occluders), and the child is allowed to search for the displaced object. Children succeed at this task by about the age of 12 months (Piaget, 1954).
In the invisible displacement task, the object is placed in a container (the displacement device) that is then placed inside or behind an occluder. The object is then invisibly transferred from the displacement device into or behind the occluder. The displacement device (now empty) is shown to the child. Children successfully search inside the occluder that the displacement device last visited once they reach the age of about 2 years (Kramer, Hill, & Cohen, 1975; Piaget, 1954). Piaget proposed that these children infer the location of the missing object because it is no longer in the displacement device.
Gorillas (Natale, Antinucci, Spinozzi, & Potì, 1986), orangutans, chimpanzees (Call, 2001), Eurasian jays (Zucca, Milos, & Vallortigara, 2007), and dogs (Gagnon & Doré, 1992) have demonstrated the ability to search accurately for visibly displaced objects. However, the evidence for accurate searches by animals for invisibly displaced objects may be problematic. Gagnon and Dore? (1993) reported that dogs search accurately for invisibly displaced objects when the object in a displacement device moves behind a screen and emerges empty. However, recent research has shown that cues provided by the displacement device and the location of the experimenter may account for the dogs' performance (Collier-Baker, Davis, & Suddendorf, 2004; Fiset & LeBlanc, 2007).
An alternative version of the invisible displacement task used by Doré, Fiset, Goulet, Dumas, and Gagnon (1996) involved the displacement of the occluder or screen after the object had been placed behind it. Doré et al. found that when the screen with the object was moved and was replaced with an empty screen, performance was very poor, but when the screen with the object was moved and no screen was moved to its previous location, performance was quite good.
Another version of the invisible displacement task used by Doré et al. (1996), which has been studied with children, involves a rotation apparatus on which three identical containers or occluders are evenly spaced (left, center, and right). The experimenter then hides a toy inside one of them and rotates the platform. Although 30-month-old children have been found to perform above chance (on average) when the object is rotated 180° (Barth & Call, 2006), if one discounts accurate searches directed at the center occluder (which remains in its original position when the platform is rotated), the children generally perform at levels below chance. …