Filler words like "um" and "er" may seem like the enemy of good speech - just ask anyone about to do a bit of public speaking - but they actually play a crucial role in helping children learn the language.

That's what Professor Richard Aslin of the University of Rochester has discovered. While lots of filler words may not be great, Aslin has discovered they're important in highlighting which words we're less familiar with, which in turn helps children recognize potential additions to their vocabulary. Aslin explains the technical term for "um" and "er" to New Scientist:

We use "ums" and "ers" 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 disfluencies. They appear in a systematic way in our speech.

Say we are looking at a toolbox and I say: "Can you pick up the... um..." In front of me there is a wrench, pliers, a screwdriver, and I'm having trouble deciding which one I want you to pick up. That's when disfluencies occur. They also frequently crop up before a word that the speaker doesn't often use.


And this, Aslin explains, helps focus children's attention on certain parts of the language that they might otherwise struggle with:

When we listen to someone speak, the words come rapidly and there is a lot of information to process, especially for children, who don't 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.

Check out the full interview at New Scientist.

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