MacDonald, E., Johnson, E., Forsythe, J., Plante, P. & Munhall, K. (2012). Children’s Development of Self-Regulation in Speech Production, Current Biology, 22, 113-117.
This study examined the use of auditory feedback across development. Auditory feedback is the mechanism by which individuals control the characteristics of their own voice, such as intensity, rate of speech, and the pronunciation of vowels and consonants. It is involved in error correction and is integral to the maintenance of coherent speech: when auditory feedback is absent or lost, changes in vocal characteristics occur.
The researchers compared compensation for formant shifted auditory feedback in 2 and 4 year olds, and adults Participants wore headphones and a microphone, and were seated in front of a computer. In order to get a robot to travel across a playground in a computer game, the participants said /bεd/ (bed). After 20 initial trials during which they listened to their own voice over headphones, the a property of the participant’s vowel known as the first formant (F1) was shifted when played back on their headphones such that they would hear themselves saying /bæd/ (bad).
MacDonald et al. (2012) found that, on average, children older than 4 years compensate for formant shifted auditory feedback, in effect ‘trying to make the word sound like ‘bed’. Children younger than 4 years of age did not tend to compensate for the manipulation. The researchers also found that speech variability decreased with age, with the youngest children tending to have highly variable word productions. Adults did compensate for the manipulations.
Future research on use of auditory feedback in very young children and toddlers, however, should determine whether motivation plays a role in production at this stage of development. In this study the robot in the computer program moved forward regardless of whether the child made use of auditory feedback and said the word correctly. Perhaps the toddlers would have compensated if it were necessary for moving the robot forward.
These findings may indicate that children have poor vowel representations at this stage of development. The auditory feedback correction mechanism does not appear to be used for vocal error correction in very young children. Perhaps this age group has not had time to develop sufficiently robust vowel representations due to the rapid growth of vocal structures at this stage. The researchers suggested that perhaps very young children are reliant on their communication partners such as parents, rather than their own internal correction mechanism.
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