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Parents shouldn鈥檛 worry about always speaking in perfectly formed sentences, says Richard Aslin. Disfluencies have their uses

You have been studying the 鈥渦ms鈥� and 鈥渆rs鈥� that litter our speech. Tell me about them.
We use 鈥渦ms鈥� and 鈥渆rs鈥� because we are having difficulties conjuring up the next word we want to say, or deciding between two alternative words. Technically they are known as . They appear in a systematic way in our speech.

Say we are looking at a toolbox and I say: 鈥淐an you pick up the鈥� um鈥︹�� In front of me there is a wrench, pliers, a screwdriver, and I鈥檓 having trouble deciding which one I want you to pick up. That鈥檚 when disfluencies occur. They also frequently crop up before a word that the speaker doesn鈥檛 often use.

I had always assumed 鈥渦ms鈥� and 鈥渆rs鈥� were useless noises, an indication that my brain isn鈥檛 working quickly enough. What does your research show?
It鈥檚 one of those things your mother tells you: 鈥淪peak in full sentences. Don鈥檛 um and er.鈥� I think it鈥檚 a view that most people have, that disfluencies are not a good thing because they don鈥檛 really communicate anything; they are just fillers.

Our shows that disfluencies in speech directed to young children have an interesting benefit. What children have learned, surprisingly early, is when there is an 鈥渦m鈥� or 鈥渆r鈥�, the word that follows is almost always one they don鈥檛 know. When you are fumbling for the correct word, you are sending a message to the child that they should pay attention. That鈥檚 very useful.

How did you find this out?
The methodology is fairly straightforward. We put pairs of photographs of objects in front of a child. One is an object familiar to the child, say a ball or banana. The other is one that they have never seen, say, a wrench. Using an eye-tracking device we can measure precisely where the child is looking. A voice says: 鈥淟ook at the ball鈥� (in a fluent way). The next sentence is disfluent: 鈥淟ook at the鈥� er鈥� wrench.鈥�

We found that when there is a disfluency, the baby will look at the object they don鈥檛 know, not the familiar one. It helps teach them new words.

Do all young children have this ability?
We showed that by two-and-a-half years of age, toddlers have developed this ability, but not at age 2. It is clearly something they have learned from listening to adults. There has been similar work which shows that adults also use 鈥渦ms鈥� and 鈥渆rs鈥� to their advantage when trying to understand speech.

Why is this important?
When we listen to someone speak, the words come rapidly and there is a lot of information to process, especially for children, who don鈥檛 know many words. The more predictions the listener can make about the words being communicated, the better they can understand. Disfluencies are useful because they help us predict which words to pay attention to.

What is the take-home message?
Parents shouldn鈥檛 worry about modest levels 鈥渦ms鈥� and 鈥渆rs鈥� in what they say to their children. Disfluencies have a benefit. They help your child to learn language.