Infants learn to speak by being spoken to, but during their first year they have difficulty distinguishing between voices in even mildly noisy rooms, said study author Rochelle Newman, PhD, a cognitive psychologist in the University of Maryland's Department of Hearing and Speech Sciences. Conversation directed at the child may simply blend into the background and go unrecognized.

Newman's study is one of the first to test the ability of infants to make sense of competing streams of speech. Specifically, it asks whether they can isolate and focus on a single louder foreground voice while several others speak more quietly in the background. Adults and older children easily handle that kind of situation.

Dr. Newman conducted a series of experiments on four groups of infants, approximately 100 children in all. She developed a series of individualized audio recordings for the study. In one, an unfamiliar female voice repeatedly called the child's name, while in the background other voices created a potential distraction. The second version differed only in that the female voice called out someone else's name.

Each infant listened to the two versions of the recording in a laboratory setting while researchers measured how long they paid attention. Dr. Newman also varied the loudness of the background noise in the recordings. She hypothesized the children would pay more attention when they heard their own names, if they could process the sounds well enough to hear them.

Dr. Newman found that the child's age made a great deal of difference. At about five months, a significantly greater number of children listened longer to their own names than to other names, but only when the background noise was very soft.

She said, "The 5-month-olds could separate the streams of conversation and focus on the voice calling to them if the background was at a level you might find in a romantic restaurant with soft and intimate conversations. But at that age the kids couldn't isolate the foreground voice if the noise level nearly doubled - what you might hear in a crowded fast food restaurant."

By 13 months, though, the children were better able to separate the streams of conversation at both noise levels. Dr. Newman concluded that this was due either to a maturing of the children's perceptual organs or a maturing of their language and listening skills. She also concluded that the infants' sensitivity to noise imposed strict limits on the kinds of settings where they might be capable of learning about their native languages.

"That first year is critical to infants," said Dr. Newman. "They're clearly struggling to hear what's said to them if there's too much noise and, at the same time, laying the foundation for learning to speak. Caregivers simply need to pay greater attention to background noise."

She suggests caregivers and parents should set aside a quiet time or a quiet corner - turning off all TVs and radios - where infants can get the language experiences they need.

This study was originally published in Developmental Psychology and highlighted in the June issue of Advance for Audiology.