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Scientific researchers who use human subjects in their work rely on their ability to speak or write to find out what they want to know. But as this Sciencentral News video reports, researchers who learn from babies don't have that luxury.
Real Head-Turners Scientists often turn to babies to learn about things like language acquisition. But learning from them isn't easy. "Anybody who has raised an infant knows that it's very difficult to get this kind of information out of a baby," says Patricia Kuhl, co-director of the University of Washington Center for Mind, Brain and Learning and professor of speech and hearing sciences. "We can't as parents ask them what they know, what they see, what they perceive, or what they're learning. So you have to be very clever in the laboratory to capitalize on the things kids do naturally."
In this case, Kuhl and her team are capitalizing on infants' natural tendency to turn their heads when they hear a change in sound, by using an adaptation of a procedure invented at the University of Washington originally designed to test infants for hearing loss. "In the original design…it was just silence in the background, and babies were encouraged to turn their heads when a sound was presented," explains Kuhl. "If they did so, the animal in the box would light up and dance. It was very, very effective in diagnosing children with hearing impairment."
Kuhl and her team wanted to see whether this test could assess a hearing infant's ability to hear the sound distinctions in speech that are critical for word learning, so they began using two sounds, one as a background sound and one as a test sound, and it worked.
By teaching the babies to turn their heads when they hear a change from a repeating background sound to a target sound, Kuhl can measure what they remember. She says that if the infants turn their heads when they hear the sounds change, that means they've learned the target sound.
But in order to be sure she's getting accurate information from the babies, Kuhl builds in what are called control trials. "Some babies might just turn their heads every ten seconds to see whether the bear or the dancing monkey will turn on," says Kuhl. "So control trials are run in which you don't change the sound and you monitor the baby for head turns in exactly the same way. If a baby is turning too often, those are called false positives. That effects your calculation of their success in making the discrimination."
But in order to be sure she's getting accurate information from the babies, Kuhl builds in what are called control trials. "Some babies might just turn their heads every ten seconds to see whether the bear or the dancing monkey will turn on," says Kuhl. "So control trials are run in which you don't change the sound and you monitor the baby for head turns in exactly the same way. If a baby is turning too often, those are called false positives. That effects your calculation of their success in making the discrimination."
Kuhl points out that the babies might act differently in the lab than at home. "In the real world, they would tend to not [turn their heads]. After the first head turn they would recognize, 'oh, yes, the sound occasionally changes, that's not new, I won't turn'. But the reason we keep them turning is that they're reinforced for doing so with this cute dancing toy. So the challenge is to advance the procedure that capitalizes on what they do naturally and turn that into a scientific way to understand what their little brains know."
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