The A not B Task

Emilie sits on her father's lap and excitedly stares at the shiny brass bell that the research assistant across the table is holding. Making sure Emilie is watching, the assistant places the bell into one of two matching wells in the table and then quickly covers both wells with identical cloths. Emilie is eager to grab the bell, as any eight-month-old would, but her father gently holds back her arms while the researcher distracts her with a funny face. After five seconds, Dad is signaled to release her arms, and Emilie uncovers the right-hand well and happily grabs the bell.

Now Emilie watches the researcher hide the bell in the other well, the one on the left. Again, Dad restrains her arms, both wells are covered, and her gaze is diverted to the experimenter's face. But this time, after another five-second delay, Emilie reaches back to the right-hand well and seems surprised not to find the brass bell in it.

Why didn't she reach to the left-hand well where she clearly saw the bell placed this time? The reason is simple; her frontal lobes aren't up to speed. Neither her working memory nor her inhibitory power are great enough to override the potent urge—or, more precisely, her procedural memory—to reach right back to the well where she had already successfully retrieved the bell.

This classic experiment was originally designed by Jean Piaget and is known as his "A not B" task, because virtually all babies Emilie's age reach for the toy correctly when it is first hidden in well "A," but err when the toy is moved to well "B." Though Piaget would attribute Emilie's mistake to the lack of "object permanence"—the memory that objects continue to exist even when you can't see them—we now know that he underestimated babies in this regard. Emilie remembers the bell's location in well B; she keeps her eyes there even as her hand is reaching to the wrong spot. Her problem is keeping this information in mind while simultaneously blocking her impulse to reach back to well A. She can do it if the interval between hiding and retrieval is short enough, no more than two or three seconds, but keeping track of everything—remembering that the bell is in well B, that she has to remove a cloth in order to retrieve it, and that she must not reach to well A—for five full seconds is simply more than she can manage.

"A not B" is harder than it seems; it requires planning, inhibition, working memory, and at least a minimal attention span—all frontal-lobe functions that are still rudimentary in babies Emilie's age. Each of these skills, however, will come to life over the next few months, as her frontal lobe kick; into action. By nine months, she can remember for as long as six seconds that the hiding place was switched, and by twelve months, she can remember it for a whopping ten seconds.


A number of complex cognitive tasks must come into play and coordinate properly for a child to recognize that an object has been moved from one hiding place to another.

Folksonomies: cognition child development

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 What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life
Books, Brochures, and Chapters>Book:  Eliot , Lise (2000-10-03), What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life, Bantam, Retrieved on 2011-07-18
Folksonomies: parenting babies development infants physiology