THURSDAY, April 7, 2005 (HealthDay News) -- A child has just secretly munched the last cookies in a box. Will she be surprised when her little brother -- who did not witness the incident -- reaches into the box for the cookies he believes are still there? Or can she grasp that people act on the basis of their beliefs, even when those beliefs do not reflect reality?
Scientists have debated the issue for decades. Some research suggests children begin to understand false beliefs at about 4 years of age. But a study in the April 8 issue of Science finds children realize at a much earlier age than previously thought that beliefs are not direct reflections of reality.
Even a child as young as 15 months seems able to understand that behavior is guided by true or false beliefs, the study suggests.
At a very basic level, these findings provide further insight into how humans think and how they interpret behavior, according to study author Kristine H. Onishi, an assistant professor in the Department of Psychology at McGill University, in Montreal.
"In order to make sense of what other people are doing, we have to think about why they do things," she explained.
On the other hand, the study adds to conflicting evidence about when children gain this ability to understand false beliefs. Is it tied to language development? Or could it be purely biological?
In an editorial appearing in the same issue, Austrian and New Zealand psychologists propose a strong evolutionary basis for understanding of belief that is deepened by a child's use of language. In other words, babies start with an implicit understanding of how the mind works, but 4-year-olds' explicit understanding is strongly related to language development.
A standard task for measuring a child's understanding of false beliefs involves having a child listen to a story as it is enacted with dolls and toys, authors Onishi and Renee Baillargeon of the University of Illinois at Champaign explain in their report. The first character hides a toy and leaves the room. A second character moves the toy to another location. Then the child is asked where the first character will look for the toy.
Four-year-olds typically get it right: They'll say the first character will look in the first location and justify their answer, the authors said. Most 3-year-olds don't: They'll say the character will look in the second location, which demonstrates a lack of understanding that the first character holds a false belief about the toy's actual location.
To simplify the task, Onishi and Baillargeon eliminated the need for children to listen to a story and give a verbal response. "We just showed the story," Onishi said.
For the experiment, 27 girls and 29 boys roughly 15 months of age were randomly assigned to watch a version of a story involving an actor and a toy placed in either a green or a yellow box. As part of the story, a change occurred resulting in the actor having either a true or false belief about the toy's location.
The scenarios differed, depending upon the actor's belief about the toy's location, whether the actor had a true of false belief, and the location the actor searched for the toy. The infants' responses were computed based on "looking times."
Researchers hypothesized that the infants would look longer if the actor behaved in an unexpected way. For example, looking times should be longer if the actor had a true belief that the toy was hidden in the green box but reached into the yellow box instead.
"Kids, like adults, look at something that's surprising," Onishi explained.
The authors' predictions were correct: The infants expected the actor to reach where she believed the toy to be and looked longer when she did not. It shows that 15-month old infants are already capable of realizing that others act on the basis of their beliefs, which may or may not mirror reality.
Beyond providing new insights into how the mind works, the authors believe their work may have another practical application. With a little tweaking, the authors said the task used to measure infants' responses might be adapted to help with the early detection of autism, a condition that affects a child's ability to communicate and socialize.
Autistic children, who generally fail standard false-belief tests, do not develop an understanding that other people have minds, Onishi said. So a false-belief test, such as the one used in the study, might yield a useful diagnostic tool. If a child repeatedly failed, "that might raise a red flag for you," she noted.
More information
The National Institute for Neurological Disorders and Stroke has more information about the brain.
