Appendix E: Speech Sound Development Summary

Appendix E

Speech Sound Development Summary

Carla Hudson Kam, PhD; Caitlin Bittman, SLP

Producing speech involves coordinating a lot of moving parts: the jaw, tongue, lips, vocal folds (what people often call vocal chords) and diaphragm (breath control is crucial to speech production) to name just a few. As children grow and mature and practise vocalizing through cooing and babbling (and yes even crying), they gain more control over the muscles involved in speech production. At the same time, their articulators themselves are maturing and developing, so they are learning to control a system that is physically changing. For instance, the size of their mouth and how much of it their tongue takes up changes a lot over the first year of life, and their teeth, which are important for the production of sounds like “f” and “th,” start to erupt. It’s a lot to handle, and not surprisingly, it takes most children several years to master the production of all of the speech sounds in their language. Every child is different, and will follow their own path. But there are some common trends in speech sound development that researchers have documented.

One way to divide sounds up is into consonants and vowel sounds. Technically, consonants and vowels are divided based on how they function in a language, but they are also generally dividable based on their articulation (how you make them) too. Vowels involve more of an open mouth, consonants typically involve some degree of contact between the articulators in the mouth. Many consonants involve contact that leads to closure of the oral cavity. Vowels are easier because they don’t involve contact. However, getting the vowel just right still involves a lot of learning. Not all consonant sounds are equally easy or hard, and there is a fairly predictable order in which children master speech sounds.

Some sounds consistently tend to be produced well(ish) early on:

• Sounds that we represent with “p” and “b,” These are called bilabial stops because we make them by closing the lips together and completely blocking the

air exiting from the mouth for a brief moment. They are early sounds for most children • “t” and “d” also tend to show up early, e.g., in early words like “doggie.” These are also stops. In English these are produced by stopping the air by putting the front of our tongue up to the hard ridge behind our teeth – called the alveolar ridge. (In other languages the tongue touches the teeth instead of the alveolar ridge) • “g” and “k” are velar stops. They are produced by stopping the airflow farther back in the mouth at a spot called the velum. They are other early consonant sounds. • The nasal sounds “m” and “n” are also early – but sometimes a child’s “b” or (“d”) might sound a bit more like “m” or (“n”), or the other way around (their “m” might sound more like “b”). This is because the two sounds are very similar, the difference between a “b” and a “m” is whether or not air is flowing through the nasal cavity (it is for “m” but not for “b”). Sometimes the child lets a bit of air through when they shouldn’t, or blocks it when they should let the air through. These small mistakes can make a big difference in the sound that we hear.

Other sounds take a long time to master:

• Sounds that involve letting some air through the vocal tract (called fricatives) are harder because we need to have just the right amount of air moving at just the right speed, or they don’t sound right. Sounds like “s” or “sh” are like this. “z,” “f,” “v” and the sound we write with “s” in the word “measure” are also English fricatives, as are the two sounds we write with “th” (the sounds at the beginning of “this” and

“think”), and languages other than English have other fricative sounds. • “r” and “l” are also often late acquired sounds. These sounds involve very specific tongue shapes and locations. R is especially interesting: the sound we write as “r” is actually very different in different languages (think about a Spanish r or French r compared to the English r). But it is always hard and late acquired.

What makes a sound easy or hard is partly about the child’s experience and partly about the articulators and movements involved. Sounds that the child can see other people produce are earlier – sounds like “p” and “b” that are articulated at the lips. It’s much easier to attempt something when we can see and hear others making those sounds. They also don’t involve any tricky tongue movements, so they are easy from an articulatory point of view. “T” and “d” aren’t as visible, but they just involve launching a movement toward a target – as long as we get the target right, we’ll get the sound right. A fricative like “s” or “z” on the other hand, involves letting just the right amount of air move through at just the right speed. If the tongue is not just the right distance from the alveolar ridge, we don’t get the right amount of air and then we don’t get a fricative: if it’s too far away then there’s either no sound (for “s”) or something more vowel-like (for “z”); if it’s too close it becomes a stop (something very “t” or “d”-like). The language itself can affect sound mastery too. Sounds that are very frequent tend to be earlier. And the function of a sound also affects its acquisition. The “th” sounds in English, for instance, are common, but they don’t play much of a role in distinguishing one word from another. In other languages where these sounds occur in more words, and so are more important for distinguishing one meaning from another, they are mastered earlier than they are in English.

People who study language development have found a lot of patterns in children’s developing (mis-) pronunciations, and we may notice our child making some of these “mistakes”:

• Consonant clusters (more than one consonant in a row, like “tr” in trick or “ns” in pins) are hard, and children often drop one of the consonants. For instance, they may say, “tick” instead of “trick” or “pata” instead of “pasta” • Children often drop consonants at the ends of syllables, saying something like “do” for dog, for example • Words with more than one syllable are often reduced, usually by dropping the unstressed syllable, so a word like “banana” becomes “nana” • Especially early on, many children often “solve” their difficulty in coordinating different movements within a word by repeating the same movement instead,

for instance, saying “baba” for bottle. This process (called reduplication) maintains the right number of syllables in the word, but makes it easier to produce. Many children drop final consonants in syllables too • Particular sounds or types of sounds can cause children difficulty, which can result in the child substituting one sound for another. Some common substitution patterns include: • “Stopping:” when children produce a stop instead of a fricative (e.g., “t” for “s”) • “Fronting:” when a child produces something more forward in the mouth than it should be, e.g. saying “t” instead of “k” • Substituting “s” for “sh” and vice versa (these sounds involve a very small difference in the location of the tongue) • Nasalization: saying “m” instead of “b” for instance, or “n” instead of “d” • Voicing and devoicing: some sounds are distinguished by whether or not the vocal folds are vibrating (say “t” and “d” while feeling your throat – “d” is voiced, “t” is voiceless). Children sometimes produce too much or too little voicing for the target sound, so a “t” comes out as a “d” or a “d” as a “t.” for instance • Most children don’t do these all the time – they might be able to say a sound perfectly in some words but not others, or in some places in a word but not in others. Sometimes they even seem to regress or go backwards. In other words, a sound our child could say before suddenly seems too hard for them. As they start producing two-word utterances, individual words can get worse.

Talking is hard! There’s so much to coordinate. Ideas have to be mapped onto the right words, then the words have be planned and produced. Multiple words have to be coordinated with each other – it’s a lot for a little brain and mouth to handle. These are perfectly normal processes, but some children do need extra help getting past these early adjustments. We can talk to our doctor or other health professional if we are concerned about our child’s speech. These professionals can help to put us in touch with the resources we and our family need to best support our child’s development.