Most adults speak to infants using so-called infant-directed speech: short, simple sentences coupled with higher pitch and exaggerated intonation. Researchers have long known that babies prefer to be spoken to in this manner. But Thiessen's research has revealed that infant-directed speech also helps infants learn words more quickly than normal adult speech. In a series of experiments, he and his colleagues exposed 8-month-old infants to fluent speech made up of nonsense words. The researchers assessed whether, after listening to the fluent speech for less than two minutes, infants had been able to learn the words. The infants who were exposed to fluent speech with the exaggerated intonation contour characteristic of infant-directed speech learned to identify the words more quickly than infants who heard fluent speech spoken in a more monotone fashion.
Thiessen's study may also explain why many adults struggle to learn a second language even though they are able to use their own language effortlessly. Children, after all, learn to speak practically from scratch, and most experts believe infants are more adept than adults at language learning.
"Learning a language is one of the most critical things that an infant has to do, because communication with other people is tremendously important," Thiessen said. "It makes a great deal of sense that the special way we have of talking to babies would help them learn."
Thiessen is director of Carnegie Mellon's Infant Language and Learning Lab, which studies how children are able to learn so much so quickly during their first few years of life. For more information, go to www.psy.cmu.edu/~thiessen/labpage.html.