By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) - A new study has supported what many people have thought for years, infants learn how to talk by listening and looking. The study 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.

A better way to say it is that infants become lip readers when they first begin producing their first speech-like sounds. They also found that this ability changes over the months as part of development.

Babies were shown videos in the first months of life 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.

What they found is not surprising – they reacted differntly to words they understood.