Feedback may control mother's baby talk
Infant speech Babies are controlling the way their mothers speak to them, according to a new Australian study, which could have implications for parents with hearing-impaired children.
The research was triggered by a case study of a mother and her twin one-year-old sons, one of whom was hearing-impaired. Kitamura noticed that the mother spoke much less clearly to the hearing-impaired son.
It's normal for mothers to speak in a special way to babies, explains Kitamura. "We call it infant-directed speech (IDS); people call it 'baby talk'."
During IDS, mothers speak in a high voice and vary intonation more than normal. They also speak slowly and clearly (hyperarticulation), which enables the vowel sounds to be readily differentiated.
Although the twins' mother used much of the IDS format with her hearing-impaired son, she was not hyperarticulating the vowels.
To test whether she had found a general effect, Kitamura looked at 48 mother and baby pairs. The babies were between six and seven months old and all had normal hearing.
Each mother was separated from her baby, but the pair could still see and hear each other on video screens.
Unbeknown to the mothers, to simulate hearing-impairment, Kitamura manipulated the sound reaching the babies. One group could hear their mother properly, a second group could hear her voice only faintly, and a third group could not hear their mother at all.
In a further twist, regardless of which group they were in, during half of the experiment the mother was told that there had been a technical hitch and her baby could not hear her.
The findings were surprising. "We found that it made absolutely no difference to the mothers' speech when they thought their children couldn't hear them", says Kitamura.
On the other hand, she says that when the babies really couldn't hear their mother, "The mothers still spoke in the infant-directed style, but they were no longer hyperarticulating vowels."
Baby in control
Kitamura concludes that the behaviour of the non-hearing babies was controlling the mother, resulting in her speaking to the baby differently, even though she didn't know the baby couldn't hear.
She says the non-hearing babies become unresponsive and their mothers quickly pick up on this.
"All that the mother is attending to is the way her baby is responding to her. If the baby is not responding, she will do something different until they do. It's probably to do with eye gaze and smiling. Smiling has a big effect on mothers," says Kitamura.
Alison Hawkins-Bond, a spokesperson for the Royal Institute for Deaf and Blind Children believes the study has important implications for how mothers of hearing-impaired children are encouraged to speak to their children.
But she points out that the brief simulated hearing loss in the experiment is a different situation from a permanently hearing-impaired child.
"We already knew that we had to use a lot of intonation", says Hawkins-Bond, "but this is saying that it is actually the vowel sounds that are used in speech that matter".
"Hearing problems are picked up at birth nowadays. Obviously professionals need to know how to support these babies, so they are not playing 'catch-up' as they did in the past."
She says the experiment shows that "the parent is switched on to getting the child's attention. Unfortunately, by doing that they are affecting the quality of their speech."