Sunday, December 19, 2010

Step 2 -The Nursery Rhyme effect - Build the brain's "Speech Sound Box"

Developing your child's “speech sound box” is critical for learning to read because learning to read depends on mapping written letters to speech sounds. Speaking to your child often, in quiet environments where there is not a great deal of noise, helps this area become finely tuned.  Nursery rhymes and nursery songs, which can be repeated over and over, are especially good for building the speech sound box.  That is probably why they  have been around for so many years and are spoken to babies around the world.  Rhymes like “Peas Porridge Hot”  and "Hickory, DIckory, Dock" are still with us, not because of the meaning they convey, but because children naturally love to hear  the repetition of words that rhyme, contain many similar sounding syllables and have repetitive starting sounds.

The way a baby’s brain begins to learn the sounds of her native language is to develop a sound map in the top part of left temporal lobe – I will call it the “speech-sound box.” Imagine that the geography of the human brain is like the map of the United States – with large cities, suburbs around those cities, and small towns, all connected by an intricate highway system. The speech sound box of a baby starts out as the hub of a central region, kind of like I imagine a major city like Atlanta might have appeared in the 1800’s.  It begins as a town near some major travel routes, with lots of  available space good for building houses, stores and churches.  Then the town grows into a city with more clearly defined streets and more closely packed buildings and larger highways that link it to other towns and cities.

Well, the child’s brain gets started in a very similar way. The right and left hemisphere of the brain have several large travel routes that have started to build before the child is born. Strategically located near travel routes are brain regions where the neurons (brain cells) will map themselves for specific jobs like perceiving color, or faces in the visual parts of the brain and distinguishing speech sounds in the listening parts of the brain.  As we learned yesterday, the baby’s brain is set up to figure out the speech sounds of the language spoken around him. That ability starts with a capacity called “categorical perception” - the capacity that underlies deveopment of the speech sound box.

Categorical perception is a skill a newborn uses to sort sounds into speech and non-speech, then to distinguish one speech sound from another. The actual physical characteristics of speech sounds are not consistent  from word to word or speaker to speaker.  The English /b/sound for example, that is in the middle of the word “baby” is slightly different from the /b/ sound that starts the word “bottle” and those, in turn, will be slightly different when produced by different speakers. But the infant’s brain is designed to figure out how those sounds are alike – what we could call /b-ness/ even though the physical properties of the sound are different, and at the same time how the /b/ sound differs from a /p/ or a /t/ sound.
Categorical perception is essential for learning speech in the first place, but it is also what then interferes with learning the sound system of another language.  That is why a native speaker of Mandarin Chinese, for example, might have trouble with the categories that distinguish an /r/ from an /l/ in English. (To the Chinese speaker they sound like the same sound.) Their speech sound box develops different categories, a slighly different map,  than an English speaker.

We know from research in infant language learning by experts like Dr. Kuhl, that new born infants are born able to distinguish the differences between speech sounds in any human language spoken in the world - so they can essentially form a speech sound box for any langauge they might end up hearing. For this reason, Dr. Kuhl has referred to very young infants as “citizens of the world.” But, by as early as eleven months of age, once the baby’s brain gets mapped for the sounds of the language spoken to them, the sound map of the brain serves as a filter that enables the baby to perceive only the sounds of the language or languages spoken in his home. At the same time the child is learning to ignore all the distinctions in sounds that might be relevant in other languages. 

Step 2 - Build the “speech sound box” through frequent repetition of nursery rhymes in quiet settings

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