What age do children lose sensitivity to sounds that are not part of the language spoken by people around them?

It's not quite accurate to say that children lose sensitivity to sounds outside their native language. Instead, they become more attuned to the sounds of their native language and less sensitive to the distinctions between sounds that are not relevant in their language. This process is called perceptual narrowing, and it happens gradually between 6 months and 12 months of age.

Here's a breakdown:

* Infants are born with the ability to distinguish between all the sounds of all languages. This is called universal phoneme perception.

* By 6 months, infants start to focus on the sounds of their native language and become less able to distinguish between sounds that are not relevant to that language. This is a natural and adaptive process that allows them to learn their language more efficiently.

* By 12 months, infants have largely narrowed their perception to the sounds of their native language. They may still be able to distinguish some sounds from other languages, but they are not as proficient as they were earlier.

It's important to note that:

* Perceptual narrowing is not complete by 12 months. Children continue to refine their phonetic perception throughout childhood.

* The process is not absolute. Children can still learn to distinguish between sounds they were not exposed to as infants, but it may be more challenging.

* Early exposure to other languages can help children maintain sensitivity to a wider range of sounds. This is why it's beneficial for children to be exposed to multiple languages from a young age.

In summary, children don't "lose" sensitivity to sounds outside their language; they become more attuned to their native language and less sensitive to distinctions that are not relevant in their language. This process is a natural and adaptive part of language development.