What babies can hear through all that noise

Listen to this short audio clip:

Now listen to this one:

Notice any difference? I didn't think so. But if you were a 5-month-old infant named Caroline, the difference would be crystal clear. In the second clip, your name would be indistinguishable from background noise, but in the first clip, you'd be able to hear it above the din. Both clips are played against the identical background noise: ten different women reading ten different stories. But in the first clip, the name "Caroline" is 10 dB louder than the backround noise, while in the second clip, it's just 5 dB louder.

Being able to separate relevant information from background noise is a complex task (just how difficult is also revealed by our most recent Casual Friday study -- if you haven't participated yet, you've still got time -- click here to try it). As we get older, the task becomes more and more difficult. But how well can babies separate backround noise from relevant information?

Rochelle Newman developed these recordings to assess infants' ability to stream speech: to distinguish relevant language from irrelevant noise. The ability to stream is likely critical to language learning -- studies have found that more than two thirds of all parents of infants report that other household members were "frequently" talking while they spoke to their babies. Add to this other noises and distractions in a typical house -- TV, pets, appliances -- and it may seem a wonder that babies can learn to talk at all.

So how well do infants stream? Newman played four recordings to 5-month-old infants, all of them like the first sample you heard above, with the baby's name being spoken 10 dB louder than the background noise. One of the recordings played the child's name, one played a different name with the same syllable stress, and the other two played completely different names. A light came on next to the speaker where the recording came from, and an independent observer recorded how long the babies looked at the light. Here are the results:

The babies looked at the light significantly longer when their own name was spoken. But when the difference was reduced to 5 dB, the results were markedly different:

Now there was no significant difference in looking time, even between the infants' own name and the non-stress-matched names. With just a 5-dB change in the level of the voice calling its name, the baby is unable to distinguish it from any other name. Newman repeated the task with 9-month-olds, and the results were the same. Only when she tested 13-month-old infants was Newman able to show that babies could reliably distinguish their name being called when it was 5 dB louder than the background noise.

Interestingly, 13 months is also the age when most infants begin to talk -- perhaps there is a connection.

Newman, R.S. (2005). The cocktail party effect in infants revisited: Listening to one's name in noise. Developmental Psychology, 41(2), 352-362.