David J. Lewkowicz, Ph.D., a professor of psychology within the Charles E. Schmidt College of Science at Florida Atlantic University, and Amy Hansen-Tift, a doctoral student, have concluded a study that shows for the first time that infants learn how to talk by listening and looking. The two-year study, supported in part by grants from the National Science Foundation and the National Institutes of Health, ispublished in the current issue of the Proceedings of the National Academy of Sciences and overturns the conventional view that infants learn how to talk only by listening to those around them.
“Our research found that infants shift their focus of attention to the mouth of the person who is talking when they enter the babbling stage and that they continue to focus on the mouth for several months thereafter until they master the basic speech forms of their native language,” said Lewkowicz, an internationally known expert on infant perceptual development. “In other words, infants become lip readers when they first begin producing their first speech-like sounds.”
In addition to offering new insights into speech development in infancy, Lewkowicz’s findings suggest a potential new way for diagnosing autism spectrum disorder earlier than is currently possible. The earliest age at which a diagnosis of autism spectrum disorder can be made currently is around 18 months of age, and one of the hallmarks of autism is that by 2 years of age, autistic children focus their attention on the mouth of a talker whereas typically developing children focus on the eyes.
“When these facts are combined with our findings, it is likely that, contrary to typically developing children, infants who are as yet undiagnosed but who are at risk for autism may continue to focus on the mouth of a native-language talker at 12 months of age and beyond,” said Lewkowicz. “If so, this would provide the earliest behavioral confirmation of impending developmental disability and would give clinicians an early start on intervention procedures aimed at lessening or preventing the most devastating effects of autism and other communicative disorders.”
To determine whether the relative amount of attention that infants devote to the eyes and mouth of a talking person changes during infancy, Lewkowicz and Hansen-Tift tested groups of 4-, 6-, 8-, 10- and 12-month-old infants. The team presented videos of women who could be seen and heard talking either in the infants’ native language (English) or in a non-native language (Spanish). While the videos played, the researchers recorded the infants’ eye gaze with an eye-tracking device and recorded how much time they spent looking at the eyes and the mouth, respectively.
The overall pattern of results prompted Lewkowicz and Hansen-Tift to draw three conclusions. First, they concluded that the initial attentional shift to the mouth provides the first solid empirical evidence that infants engage in lipreading when learning how to talk and, thus, that acquisition of speech production capacity is a multisensory rather than an auditory-only affair. Second, the researchers concluded that the subsequent shift back to the eyes reflects the development of native-language expertise, as well as the need to focus attention on socially relevant cues available in the speakers’ eyes so as to continue developing increasingly more sophisticated cognitive abilities.
Finally, the persistence of lipreading in response to non-native speech was interpreted as reflecting early native-language experience, which simultaneously increases infants’ expertise for native speech and narrows their ability to perceive non-native speech. The consequence of this is that older infants can no longer understand non-native speech and, as a result, when exposed to it, they attempt to disambiguate it by continuing to rely on the greater salience of audiovisual speech.
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