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Can your baby hear your smile?

Mother smiling and talking to her new babyHave you ever thought about how you can tell if someone is smiling or frowning when you speak to them over the phone? New research suggests that babies may also be able to hear whether you’re smiling – even if they don’t understand the words being said.

The fact that we can hear smiles, even if we can’t see them, has to do with how our speech changes when we smile – hear for yourself by saying the sound ‘sss’ while slowly changing your lips from a broad smile to a solid frown, and back. The ‘sss’ sounds higher when you smile, and lower when you frown.

While pitch is the fundamental frequency of a sound, speech sounds also have a whole array, or spectrum, of frequencies. When you change the shape of your lips, you hear the spectral frequencies change. It is the higher spectral frequencies you hear in this example that are characteristic of smiled speech, while the lower spectral frequencies are characteristic of frowned speech.

Research findings

In a first step towards discovering if babies can also hear the difference between smiles and frowns, we created speech stimuli that only differ in these spectral frequency characteristics. We then re-recorded sentences from an audiology test (selected because they’re meaningless to 6-month-olds) and artificially changed the frequency characteristics of the sentences.

We found that 6-month-old babies preferred listening to the sentences with raised, rather than lowered, spectral frequencies [1]. This is the first evidence that 6-month-olds base their listening preferences on the spectral frequency characteristics of adult speech. These results show that infants have the basic sensitivity that is needed to hear the difference between smiles and frowns!

These findings suggest that parents trying to attract their baby’s attention, may be more successful if they speak to them with a smile – even if their baby doesn’t look at them yet!

Knowing that 6-month old babies prefer speech with these higher spectral frequencies, means we can now start to find out whether this type of speech also benefits activities that require a baby’s attention, such as language learning.

Many thanks to the parents and children who volunteered their time to this research! Parents and children who are interested in participating in future research can find out how at the Child Language Lab participants page.

1.Benders, T. (2017), Six-Month-Old Infants Prefer Speech with Raised Formant Frequencies. Infancy. doi:10.1111/infa.12190

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