There's a very well-known experiment in developmental psychology called the "A-not-B task." The experiment goes something like this: you, the experimenter, are seated opposite a human infant. Within the reach of both you and the child are two boxes: box "A," and box "B." You hide a toy in "A," in full view of the infant. As expected, the infant reaches for "A" to retrieve the toy. You repeat the process several times. Each time you hide the toy in "A," and each time the infant reaches for "A" to find the toy. Experimental set-ups like this are extremely common in infant and animal studies. When trying to determine how a young baby - barely able to interact with you or the world - thinks about the world, you've really got two options: design an experiment that relies on the infant's ability to direct his or her eye gaze to a given location, or one that relies on the infant's ability to (somewhat clumsily) reach towards a given location.
So you keep hiding the toy in "A" and the baby keeps searching for the toy in "A." Simple enough. But what happens if you suddenly hide the toy in "B"? Remember, you're hiding the toy in full view of the infant. An older child or an adult would simply reach for "B" to retrieve the toy. But not the infant. But, despite having just seen the object hidden in the new "B" location, infants between 8 and 12 months of age (the age at which infants begin to have enough motor control to successfully reach for an object) frequently look for it under box "A," where it had previously been hidden. This effect, first demonstrated by Jean Piaget, is called the perseverative search error or sometimes the A-not-B error.
The A-not-B error is one of the most replicated findings in developmental psychology, but it seems almost as if for every time the experiment and results have been replicated, there has been a new explanation presented for why the error itself even occurs. Piaget thought that the existence of the object under A is causally related to the search response itself. That is, independent of where the object was hidden, searching under A would result in the object being found at A. In other words, he thought that the error reflected the immaturity of the child's understanding of object permanence, which is the understanding that objects continue to exist even after they become hidden. When a ball rolls under a couch, according to Piaget, an infant with incomplete object permanence would behave as if the object ceased to exist since it is no longer visible. Other more recent explanations have suggested that the infants are unable to inhibit a previously rewarded motor response, perhaps reflecting the immaturity of the prefrontal cortex, or that the error is due to limitations on working (short-term) memory. Others have suggested that infants are unable to switch their attention from location A to location B, presumably also due to underdeveloped executive functioning in the prefrontal cortex. This would reflect perseveration in attention rather than in search behavior, per se. Yet others have implicated the putative mirror neuron system to explain the error.
When experiments get replicated, even under the best of circumstances, there are minor tweaks in the way the experiment is conducted, like in the game telephone. What is especially remarkable, then, about the A-not-B error is that despite the methodological differences in conducting the experiment, the results are extremely consistent. Even if developmental and cognitive psychologists can't agree on why the error occurs, that it occurs is certain. But a finding without a solid explanation isn't particularly useful, is it?
One way to better determine the reason for the A-not-B error would be to find a way to break it. This isn't necessarily a ground-breaking idea: the common errors children make when learning to read, for example, tell us important things about the process of learning to read. When Dan Simons and Chris Chabris discovered inattentional blindness - essentially a breakdown in the attention system - that told researchers something really important about how attention works in the first place. So, are there any circumstances under which an infant under 12 months of age would reliably pass the test, and search for the toy at location B on the B trials?
A group of researchers from Hungary, including Hungarian rockstar developmental psychologists Gyo