The perseverative search error seems to be a function of social interaction and not of cognitive development. Perhaps I should elaborate for those of you unfamiliar with this reasoning error (as I was until quite recently).
The perseverative search error, also known as the A-not-B error, is routinely made by children between 8 and 12 months. It goes like this: If you hide an object in location A a few times, and then hide the object in location B, babies will continue to search for the object at A. This is true even if the child clearly sees that the object was placed at B. You can see an example of this highly replicated finding below.
There have been many explanations for this occurrence, including that very young children are cognitively incapable of switching their focus to another location, and that they are incapable of remembering recent events. However, researchers from the Hungarian Academy of Sciences conducted an experiment that rules out those possibilities. Instead, it seems that perseverative search error is a product of social interactions.The Hungarian scientists performed the A-not-B test in the usual manner, which involves a lot of talking and eye contact. They also ran the tests in situations where the experimenter did not talk to or make eye contact with the child, and in situations where there was no one present with the child. In the first case, they got the usual result, i.e. the child made the A-not-B error most of the time. However, in the latter two tests, babies were fooled less than half the time. In other words, the perseverative error is not a function of babies’ brain development but rather is induced by social contact.
This finding could have implications for all sorts of cognitive studies done on young children. Researchers will have to be sure they are not testing babies' abilities to interact socially rather than their ability to reason.