Speech sound production is a complex task that takes time to develop. Children born with typical hearing, only use reflexive vocalizations (i.e. crying, grunting, coughing and sneezing) for the first few months of life. Next, cooing begins, followed by some vocal play/repetitive babbling. True babbling doesn’t even begin until 6-10 months of age.
Each speech sound requires a different sequence of movements of the oral musculature. Some sounds require more gross (larger scale movements) while others require more precision. It is because of this that there is a developmental progression that occurs as children learn to produce different sounds. For children with typical hearing, a range of expectations has been determined based upon research. For children with hearing loss, we need to consider the hearing age and auditory access to speech (with hearing aids or cochlear implants) in tandem with these milestones. Using Sander’s research, (Sander, E. (1972). When are Speech Sounds Learned? Journal of Speech and Hearing Disorders, 37, 55-63), I have created a general break down of expected ages for early, middle and late developing sounds for children with typical hearing. With consideration of hearing age, a child with hearing loss should generally follow a similar progression. I have also added some information as to how auditory access, or the ability to hear these sounds, can impact upon a child’s ability to accurately produce the sounds.
The Early Sounds
The first sounds that typically develop are /p,m,h,w,b/. These sounds generally use movements of the jaw and lips and require the least amount of motor precision. Generally 90% of children with typical hearing have mastered these sounds by age three.
For children with hearing loss these are sounds that can easily be “seen” and thus, the motoric patterns can be imitated regardless of auditory access. However, many of these sounds look the same when made, so being able to hear the differences is necessary to accurately produce these sounds. For example, the sounds /p,b,m/ are all made by putting the lips together. The differences are what you do with you vocal cords and whether or not the sound resonates in
your nose.
The sound /n/ is also usually mastered by 90% of children with typical hearing by age three. This sound is different, however, in that it is made with the tongue. The tongue tip elevates behind the teeth for this sound. However, at first children often use the middle of their tongues before making the sound more precisely. This sound is less visible than the sounds listed above.
Among this grouping of sounds, /b,m,w/ are lower in frequency then /p,h/. So a child’s ability to hear the higher frequencies may impact upon production of these higher frequency sounds. The sounds /m,n/ are often most audible for children with residual hearing in the low frequencies, as the sound resonating in the nose is low frequency energy.
The Mid Sounds
During the next wave of sound development, children begin to learn how to move their articulators more precisely. By age four, 90% of children with typical hearing have mastered production of /t,d,k,g,ng/. Each of these sounds are more difficult to see as they are made inside the mouth. The first two sounds in the list, /t,d/, are made like /n/ with the tip of the tongue elevating. The remaining sounds /k,g,ng/ are all made with the back of the tongue. During typical speech development, children often take time to learn how to lift the back of the tongue for /k,g/. They say “tat” for cat and “pid” for pig. This may also be seen for children with hearing loss. The sounds /t,k/ are the highest frequency sounds at this stage. The remaining sounds have vibration of the vocal cords, which provides low frequency information.
The sounds /f,y/ typically begin to emerge around 2 ½ and are mastered by 90% of children by age four. The sound /f/ is a very visual sound, but is sometimes difficult for a child to produce as it requires placing the top teeth on the bottom lip. Auditorily, /f/ is a very high frequency sound, so for a child with a high frequency hearing loss, it is often a difficult sound to hear. However, with appropriate amplification (hearing aids or cochlear implants) access to this sound is often achievable.
The Later Developing Sounds
The remaining sounds /l,r,s,ch,sh,z,j,v,th/ are the latest developing sounds. These sounds are typically mastered between the ages of 6 and 8 by 90% of children with typical hearing. They require the most motoric skill. These are the sounds for which children with normal hearing often receive speech therapy. The ability to accurately hear these sounds greatly impacts a child’s ability to produce the sounds correctly as slight changes in placement of the articulators can make them sound wrong. The sounds /s,sh,th/ are the highest frequency sounds in this list, so optimal amplification is required for access and accurate production.
So What Does All This Mean?
As you watch your child’s speech develop, you need to take into consideration the normal progression of speech sounds, your child’s hearing age, and current auditory access with amplification. Each of these factors together are an indicator of when your child will accurately produce the specific speech sounds. However, if based upon the above, you feel your child should be able to produce a certain sound, but can’t, specific motor speech therapy might be required. For example, if your child was implanted around one year of age, has excellent access to speech in the top of the “speech banana” with amplification, and is 9 years old, we would expect accurate production of the later developing sounds. If not, specific work on placement might be needed.