Retrospectacle: A Neuroscience Blog

Object permanence refers to the notion that objects are separate entities that continue to exist even when we can't see them. Its the opposite of "out of sight, out of mind" in the sense that the person (or animal) realizes the object still exists in space somewhere. This may lead to searching behavior, or a memory of where the object last was placed. Human children are not born with object permanence--it develops over the first two years of our lives. This was quite a big discovery that made a psychologist named Piaget very famous in the 1950s. Turns out, African grey parrots share this ability as well! How that became known and tested is continued below the fold.

Piaget showed that, in children, object permanence happens in stages. In Stage 1, children do not search for an object once it is covered up. They just assume it no longer "is." In Stage 2, children track an object, in stage 3 they recover a partially-visible item, and in stage 4 they recover a fully occluded item. In stage 5, a child will recover an item hidden, exposed, and rehidden several times. And in stage 6, they can retrieve an item hidden in a secondary box even when they did not see the item being transferred to another box (think "the shell game"). This is the "Piagetian framework." The stages occur in order, progressively and are dependent on the age of the child.

Object permanence has also been examined in other species:higher primates, some parrots, and perhaps dogs were thought to reach stage 6, while cats, monkeys, doves, rodents, and chickens did not. Irene Pepperberg published a study in 1997 tracking how developing African Grey Parrots exhibited object permanence as they matured. The primary subject of the test was a African Grey named Griffin, who was 8 weeks old at the beginning of the study. This is an extremely young parrot who neither has his feathers, or is weaned.

Pepperberg would hide one of his toys, or a bit of food, similar to the stages of the Piaget framework and observe when Griffin was able to uncover the item. Experimenters were changed during the trials to eliminate the possibility of the bird reading the handler's cues. The results are listed in this table View image".

The results showed that by 21 weeks old, Griffin had obtained stage 6 object permanence although he could not succeed at the shell game specifically until week 52. In addition, Griffin showed a gradual and step-wise development along the Piaget framework, in a similar cognitive development pattern as higher primates (such as humans). While this task can only hint at the cognition behind the behavior, it is interesting and fascinating to see complex and phase-dependent cognitive development on a task which indicates a high level of environmental awareness in a very different species than us.