Do babies understand that things exist when they're out of sight, or don't they?

When babies younger than nine months watch as an object is placed under a cloth, most will subsequently act as though it no longer exists - that is, they don't go looking for it. The pioneering developmental psychologist Jean Piaget thought this reflected the fact that babies of a certain age are unable to grasp the idea that objects continue to exist even when they are out of sight - what psychologists call "object permanence".

However, more recently, developmental psychologists have shown that young babies spend longer looking at a situation that appears to contradict object permanence (e.g. the object is no longer visible once the cloth is lifted), almost as though they're surprised that the rules of physics have been broken. These "looking time" experiments have led some experts to suggest that babies do have an understanding of object permanence, it's just that they lack the bodily coordination to look for hidden objects, or they lack the memory capabilities required to remember that the hidden object is still there.

Now Keith Moore and Andrew Meltzoff have cast some fresh illumination on these controversies. They found that the majority of the thirty-two 8.75-month-old babies they tested were able to lift a cloth to reveal a partially hidden toy, but failed to lift a cloth to reveal a completely hidden toy. This shows that it's not a lack of coordination that prevents young babies from passing tests of object permanence.

A second experiment showed that some 10-month-olds but none of the 8.75-month-olds benefited when a completely hidden toy emitted a noise. This suggests that it's not a memory issue causing the younger babies to fail to look for the hidden toys because presumably the noise would serve as a reminder.

Moore and Meltzoff think that the discrepancy between the looking time experiments and reaching experiments can be explained by the fact that they place different demands on the babies. In the looking time experiments, the babies have to compare what actually happened (i.e. no object) with the prior state of affairs (i.e. an object was there) whereas the reaching experiments are more difficult in that the babies have to make a prediction about what the future situation will be if they lift the cloth.
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MOORE, M., MELTZOFF, A. (2008). Factors affecting infants manual search for occluded objects and the genesis of object permanence. Infant Behavior and Development, 31(2), 168-180. DOI: 10.1016/j.infbeh.2007.10.006

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