Speech and language development for children with Down syndrome
This section provides an overview of the main ways in which speech and language development for children with Down syndrome may be different from the typically developing child. It describes the delays that are usually seen and comments on some of the reasons. Activities to improve the progress of babies and children with Down syndrome at each stage from birth onwards are set out in the practical modules that accompanies this one.
It can be disheartening to read a list of the difficulties caused by having Down syndrome, particularly if you are a parent. However, the author believes that we will only be able to develop effective interventions if we understand the specific difficulties and design interventions to target them. In the past twenty years this approach has led to more effective interventions and to a greater appreciation of the strengths of the children.
Summary of the speech and language profile of individuals with Down syndrome
- Speech and language skills are specifically delayed relative to non-verbal abilities
- Non-verbal communication in infancy and later is a strength
- Use of gestures to communicate is a strength
- Vocabulary is learned slowly but steadily and becomes a strength
- Spoken production of words lags behind comprehension
- Early grammar is learned slowly and paced by vocabulary size
- More complex grammar is specifically delayed relative to vocabulary
- Spoken production of grammar lags behind comprehension of grammar
- Difficulty with speech production - first spoken words delayed, strings of words difficult
- Phonology is a challenge, therefore speech intelligibility is a weakness
- Teenagers and adults often still communicate with short, ‘telegraphic’ sentences
It is important to remember that no two children are alike and that there is just as much variation in the rates of progress and individuality of children with Down syndrome as there is among all children. This issue of variation is explored more fully towards the end of this section.
It is also important to remember that the communication skills of children with Down syndrome are a strength. They want to communicate and do so effectively in the early years and later, using gesture to compensate for their difficulties with spoken language. We all continue to use gesture and non-verbal communication skills throughout life but individuals with Down syndrome may make more use of these to compensate for their spoken language difficulties.
Early communication skills
Most babies with Down syndrome have good early non-verbal skills. They may make eye-contact, look and smile a little later than the typical infant. Once the babies begin to interact in this way, they like to communicate and enjoy smiling and babble games. They take a little longer to reach each stage but they usually develop good joint attention skills at about the same developmental stage as other children Hahn ref . They respond to joint attention when initiated by and adult but may be a little later to start initiating them. This is a good foundation for being social and wanting to communicate, which continues through life for most children.[1]
However, babies with Down syndrome are slower to move on to explore the physical world around them, both visually and by interacting with objects and toys.
They find it more difficult to maintain their attention on a toy or activity, and to keep switching attention from one toy or activity to another. Research with babies with Down syndrome has shown that it is very important to be responsive and to follow the babies’ lead and to talk about what they are already doing and attending to. For example, in one study, the mothers of typically developing children who kept initiating new activities for the child, had children with bigger vocabularies later. However, for the babies with Down syndrome in the study, this strategy did not help them. In this group, the mothers who followed the child’s lead and did not try to keep switching the child’s attention had children with larger vocabularies when they were older.[2]
Gesture
Most children with Down syndrome from about 18 months of age begin to imitate gestures, learning to wave and to point, just like other babies. They will go on to learn more gestures and to use gesture naturally as they get older. A number of research studies have highlighted that the use of intentional gestures to communicate is a particular strength for children with Down syndrome, and that they are sometimes even better at using gesture than typically developing children at the same level of cognitive ability.[3–5]
Many children with Down syndrome will be frustrated by delay and difficulty in producing clear words, but will be able to learn specific signs to use instead of words at this stage (about 2 to 4 years). This will help them to communicate when they do not yet have the words that they need to convey their message or when their speech is not understood. The benefits of teaching signs to aid both comprehension and production of words at this stage will be discussed later in this module.
Talking - vocabulary
Most children with Down syndrome are late in starting to talk. The average age for the first spoken word is about 18 months and for the first ten words, the average is about 27 months. Like other children, children with Down syndrome start using two words together when they have a productive vocabulary of about 50 different words. This occurs at around 37 months on average.[6–8]
After this, progress is usually steady but slow. The children begin to use three and four word sentences and to learn grammatical markers and different sentence structures.
However, most children with Down syndrome understand significantly more than they can say. Jon Miller and his colleagues, at the Waisman Centre, University of Wisconsin - Madison, USA, have carried out several comprehensive studies of early vocabulary development in children with Down syndrome. [16-18],[9],[10]
Firstly, they have identified three profiles of early language development among the children with Down syndrome. One third (34%) of the children had the language production skills that would be expected for children with their level of language comprehension and non-verbal mental abilities. However, the majority of children (64%) had language production skills that were poorer than expected for their language comprehension skills and non-verbal mental age measures. Only a small number of the children’s profiles (2%) showed language production behind language comprehension, with comprehension behind non-verbal mental age.
Secondly, their data shows that as the children grow older, the proportion that have language production skills lagging behind comprehension, increases to some 85% or more.
This research indicates that for many children with Down syndrome, even the production of first words lags behind their comprehension of words more than it does in typically developing children. This is a very frustrating situation for them and being able to sign at this stage will help them to communicate more effectively. If they can indicate their understanding by signing, this will encourage parents and carers to keep talking and including them in conversations.
Speech
Most children with Down syndrome find all aspects of speech production difficult.[11] While a number of studies indicate that babies with Down syndrome babble normally, they seem to struggle to say single words as early or as clearly as their typically developing peers.
They then find producing three and four words in a sequence difficult. Even words that they can say clearly as single words, become less clear when produced as part of a sentence. This was illustrated in a study of 9 children with Down syndrome over a four-year period by Hart.[12] She states ‘’the observers commented on the difficulty the children seemed to have in articulating more complex statements. The excessively rapid speech made most such extended statements largely unintelligible, so that listeners seemed regularly to ask the children to state their ideas more simply.’’ [67, p.219][12]
Hart concludes that ‘’All children in the study could have benefited during the prelinguistic period from therapy directed towards motor control of the tongue, mouth and vocal tract as well as exercises emphasising rhythm and pacing, awareness and control of starting and stopping gestures and sounds, and of gradually or abruptly increasing and decreasing their speed and volume’’. [67: pp 219-220][12]
There are almost certainly many complex reasons for these speech production difficulties, most of them needing further research. However, it is likely that many, if not most, children with Down syndrome discover that they are more likely to be understood if they use only two and three word utterances, thus increasing the chance of producing those words clearly enough for them to be recognised.[11],[13],[14]
These production difficulties will, in turn, influence input to the children and therefore their language learning opportunities. Communication needs a partner and it is likely that babies and children who are not producing sounds, words or sentences are spoken to and included in conversations much less frequently than those who are. This will be a significant risk from babyhood right through to adult life.
There is limited but consistent evidence that speech therapy can improve the children’s ability to speak clearly and that parents can effectively carry it out. This work is described in detail later. [69-71]
Grammar and sentence structures
Figure 1. The links between vocabulary and grammar, showing the 50th, 10th and 90th percentiles for typically-developing children and for children with Down syndrome
Most children with Down syndrome struggle to learn the full grammar of their language. However, they do begin to join words together when they have a vocabulary of about 50 words, like other children, and they do show the same progress with grammar when their vocabulary reaches 300 words.[15] The scatterplot in [Figure 1] illustrates the way in which early grammar in the children’s speech was increasing as their total vocabulary size increased. The blue lines are percentile lines and they indicate the range of progress expected for typically developing children, as reported in Bates and Goodman.[16] The points on the scatterplot indicates the vocabulary size and grammar score obtained by each child with Down syndrome, as reported by their parents on the MacArthur Communicative Development Inventory (CDI). These 92 children with Down syndrome (percentiles indicated by the red lines) show essentially the same relationship between vocabulary size and grammar development as typically developing children.
Slow progress
The children with Down syndrome in this study are from 3 to 8 years of age. The blue lines represent progress for the typically developing children from 12 to 30 months of age. In other words, the development of the children with Down syndrome shows the normal link between vocabulary size and grammar, but they are acquiring vocabulary at a very slow rate. John Locke’s theory discussed earlier would suggest that this very slow vocabulary progress could be leading to the delayed grammatical development for children with Down syndrome. Most adults with Down syndrome have mastered only the simple grammar achieved before 5 years by most typically developing children.[17] Locke’s view would also suggest that phonological development - that is fully flexible control over the production of speech sounds in words - will also be inevitably delayed by the slow vocabulary acquisition.
Working memory
As children with Down syndrome get older their knowledge of vocabulary tends to be significantly ahead of their comprehension of grammar. In addition, as emphasised above, their production of grammar lags behind their comprehension of grammar. It has been suggested that this may be the result of difficulties with auditory processing and verbal short-term memory.[18], [TODO: references 8],[19],[20],[16] Children with Down syndrome have smaller short-term memory spans than other children of similar age and this will limit their ability to process sentences. These difficulties are explained more fully in the working memory module in this series.
Many teenagers are still using phrases made up of key words but without the function (joining) words or all the grammatical markers. For example, saying ‘he sit chair’ instead of ‘he is sitting on the chair’. This is referred to as ‘telegraphic’ speech.[21],[22]
No absolute ceiling
Intelligibility
Research points out that people with Down syndrome have difficulty with communicating clearly, and that people close to them learn to accommodate these difficulties:
In a survey of 937 families in America carried out by Libby Kumin and colleagues, 58% of the parents reported that their children with Down syndrome frequently had difficulty being understood, whereas only 5% reported that their children rarely or never had difficulties.[23]
A survey of 90 families in the UK in 1987 produced similar findings, with parents reporting that only 42% of teenagers could be understood by strangers when they were out in the community. However, when this study was repeated in 1999, 78% of teenagers who had been in mainstream education and 56% of those from special education could be understood when out in the community. Parents and teachers understood 90% of the teenagers in both studies. Intelligibility has been improved by inclusion in mainstream schools from infancy.
Robin Chapman and her colleagues, also of the Waisman Centre at the University of Wisconsin - Madison, have carried out the most extensive studies of the development of speech and language skills in older children. Their data shows that most teenagers with Down syndrome are still making slow but steady progress with productive grammar as they get older. That is, they have not reached a ‘ceiling’ and they continue to develop the use of longer and more grammatically complete sentences. [76-79] This is the case even when teenagers receive little or no speech and language therapy. Effective interventions into adult life would be likely to help most young people with Down syndrome improve their vocabulary, sentence structures and clarity when speaking.[19],[24]
This view is supported by the author’s intervention studies with teenagers, which provided activities targeted at production of grammar in sentences. This training over the period of one school year led to increases in conversational utterance length and grammatical complexity in the speech of the teenagers (see details of this study in the ’ [Teaching grammar]’ section).[21],[25]
Intelligibility
Joining in
The spoken language of many children and teenagers with Down syndrome is not always understood, especially by people not familiar with them. This is largely the result of poor speech clarity but it is probably also influenced by the telegraphic style as well. This will be very frustrating for children with Down syndrome and may lead to them being reluctant to initiate conversations as they often fail to make themselves understood. They will have more experience of successful conversations when they join in rather than start the conversation. If you join in, everyone already knows the topic of the conversation and therefore your contribution is more likely to be understood. This effect has been demonstrated in at least one research study with teenagers with Down syndrome.[14] Being able to join in with friends of the same age is particularly important in teenage years for developing friendships, being included in social and leisure activities and for independence.
Familiarity
Parents and teachers, who spend time with young people with Down syndrome regularly, may underestimate the communication difficulties that they will experience when trying to talk to people who have not known them long enough to become familiar with their speech.
Milestones and individual differences
[Table 5] provides a guide to expected rates of development in expressive language skills but the reader should remember that the majority of children with Down syndrome understand more advanced spoken language than they can produce when they talk. The reader should also note that, while the use of spoken language is delayed, the communicative uses of language listed in the ‘Interaction’ column are much the same as other children, at much the same age. In other words, children with Down syndrome want to express and share the same things as everyone else but they are restricted in the ways in which they can do so. The table gives a guide to average progress and there is considerable variation in rates of progress between individuals with Down syndrome. This variation is discussed further later in this section.
Table 5. Typical production milestones for children with Down syndrome
| Age | Interaction | Vocabulary | Grammar | Speech |
|---|---|---|---|---|
| 0-12 months | Crying Eye-contact Smiling Listening/looking Vocalising - coos Turn taking | Understanding words |
Babble Babble tuned to native language |
|
| 12-24 months | Joint attention Gestures Conveying an increasing number of meanings in gestures and some words | Beginning to sign Beginning to say Words First 10 words | Initial consonants and vowels developing as single sounds | |
| 24-36 months | Initiating conversations - pointing, requesting | First 30 words Comprehension ahead of production | Two words together | Words not very clear/intelligible |
| 36-60 months | Repairing conversations when not understood - by trying again | First 100 words Rate of word learning increases At 5 years about 300 words | Two and three key words together Early grammar begins | Consonant, vowel and word production improve in accuracy |
| 5-7 years | Learning to tell short narratives | Vocabulary learning continues to accelerate At 7 years about 400 words | ‘telegraphic’ sentences - keywords Increasingly correct short sentences | Consonant and vowel production continue to improve in accuracy |
| 7-16 years | Taking part in longer topic related conversations Requesting clarifications using - What?, Where Telling stories Developing social use of language further - social small talk Taking account of listener’s knowledge knowing how to provide appropriate amounts of information for person or social situation Giving longer explanations or instructions Telling jokes Recounting experiences | More new words are learned each year Typical vocabulary size of older children and teenagers not known | Correct syntax being mastered slowly More difficult prepositions ‘above’, ‘below’, conjunctions ‘and’, ‘then’, ‘because’, comparatives - ‘longer than’ Grammar steadily extended to include passives in comprehension Many of these features are learned and used in reading and writing and then in speaking | Blends improve Speech becomes steadily more intelligible Speech rate and speech clarity continue to improve, influenced by reading |
Individual differences
Table 6. Age at which children reach 10 word and two word phrase stages (adapted from Oliver and Buckley[7])
| 10 word stage | 2 word phrases consolidate | |
|---|---|---|
| Number of children | 9 | 14 |
| Average age (months) | 27.3 | 36.8 |
| Range of ages (months) | 19 - 38 | 25 - 52 |
All research studies document the wide range of individual differences in progress with speech and language development among children with Down syndrome. The variation in rates of progress for children with Down syndrome is illustrated for individual children in the diary records kept by their parents during a study conducted by the author and colleagues.[7] In [Table 6] the age at which children reached 10 words in their spoken vocabulary and then the age at which they began to put two words together are illustrated. Some children were saying 10 words 19 months before others and some were putting 2 words together 2 years before others. These differences may be due to a number of factors, including level and frequency of hearing loss, extent of sound production (phonological) difficulties, degree of learning disability and the amount that the child is being talked to.
[Table 7] shows the ages for individual children reaching 10 spoken words and putting two words together when speaking. Interestingly, if adjusted, as in the last column for the 12 month delay in reaching 10 words, the children with Down syndrome only seem to take the same length of time as other children to go from first words to begin to put two words together in their speech. This may be because their understanding is in advance of their vocabulary production skills and they are wanting to express two word meanings in their communication, despite having only a small total vocabulary at this time.
Table 7. Individual profiles for early language production (adapted from Oliver and Buckley[7])
| Age at 10 word stage (months) | Age at 2 words together stage (months) |
Age 2-word phrases adjusted to account for estimated 12 month delay at 10-word stage (months) |
|
|---|---|---|---|
| "A.L" | 23 | 31 | 19 |
| "M.M" | 24 | ||
| "F.M" | 23 | 30 | 18 |
| "T.M" | 22 | 25 | 13 |
| "E.C" | 31 | 39 | 27 |
| "E.O" | 19 | ||
| "M.T" | 38 | ||
| "A.T" | 30 | 36 | 24 |
| "V.W" | 36 | 41 | 29 |
| "H.A" | 34 | 22 | |
| "K.G" | 33 | 21 | |
| "H.H" | 33 | 21 | |
| "N.H" | 49 | 37 | |
| "F.K" | 40 | 28 | |
| "M.N" | 42 | 30 | |
| "L.O" | 31 | 19 | |
| "D.V" | 52 | 40 |
Recently, the author and colleagues collected information on the language progress of 210 children with Down syndrome, using the MacArthur Communicative Development Inventories.[26] In [Table 8] the data for spoken words at each age group is given and in [Table 9] data for the words understood. The data in the columns reporting the ranges in both these tables again emphasise the widely differing rates of progress for different children with Down syndrome. For each age group the children understand more words than they can say.
Table 8. Total spoken words in the vocabularies of children with Down syndrome (adapted from Buckley, Pennanen and Archer, in preparation [TODO: references 115])
| Age in months | Number of children in group | Mean spoken vocabulary size | Standard Deviation | Range of spoken vocabulary sizes |
|---|---|---|---|---|
| 15 - 23 | 12 | 10.7 | 12.7 | 0-38 |
| 24 - 35 | 17 | 28.1 | 34.9 | 0-125 |
| 36 - 47 | 44 | 116.7 | 102.9 | 1-399 |
| 48 - 59 | 26 | 247.8 | 144.9 | 22-481 |
| 60 - 71 | 32 | 271.6 | 180.4 | 8-586 |
| 72 - 83 | 39 | 330.4 | 174.8 | 0-640 |
| 84 - 95 | 32 | 390.5 | 160.6 | 80-615 |
| 96 - 107 | 8 | 434.2 | 184.5 | 166-604 |
| Total | 210 |
These data tables are included to give parents, teachers and therapists some guidelines as to the expected rates of language progress for children with Down syndrome. In the author’s experience it is useful to know whether a child is progressing faster or slower than might be expected for their age, in comparison with other children with Down syndrome, when planning teaching activities and advising parents.
Table 9. Total words understood by children with Down syndrome (adapted from Buckley, Pennanen and Archer, in preparation [TODO: references 115])
| Age in months | Number of children in age group | Mean size of vocabulary | Standard Deviation | Range of vocabulary sizes |
|---|---|---|---|---|
| 15 - 23 | 12 | 124.8 | 77.1 | 34-254 |
| 24 - 35 | 17 | 166.9 | 101.0 | 25-309 |
| 36 - 47 | 43 | 233.4 | 93.0 | 69-424 |
| 48 -59 | 26 | 300.2 | 121.3 | 88-505 |
| 60 -71 | 31 | 334.4 | 148.6 | 80-586 |
| 72 - 83 | 38 | 360.8 | 153.6 | 62-642 |
| 84 - 95 | 32 | 416.8 | 147.7 | 90-628 |
| 96 - 107 | 7 | 471.9 | 162.4 | 215-604 |
| Total | 206 |
[Table 10] illustrates the progress with the early stages of grammar as measured for 84 children on the MacArthur Communicative Development Inventory. While there is steady improvement with age, there is considerable variation at each age level. Of the 210 children in the study, only 84 obtained a score on the grammar scale, the rest of the children had not yet reached this stage. The average production vocabulary in the grammar group was 416 words and the average production vocabulary in the no grammar group was 154 words, again supporting the view that the development of grammar requires a minimum vocabulary size.
Table 10. Mean, standard deviation and range of total complex phrases used (adapted from Buckley, Pennanen and Archer, in preparation [TODO: references 115])
| Age in months | Number of children in age group | Mean number of complex phrases | Standard deviation | Range |
|---|---|---|---|---|
| 36 - 47 | 7 | 4.9 | 7.2 | 1-21 |
| 48 - 59 | 12 | 7.4 | 7.7 | 1-25 |
| 60 - 71 | 14 | 10.3 | 8.1 | 1-24 |
| 72 - 83 | 21 | 13.0 | 9.3 | 1-30 |
| 84 - 95 | 24 | 16.6 | 9.6 | 1-34 |
| 96 - 107 | 6 | 18.7 | 11.0 | 2-33 |
| Total | 84 |
Table 11. Mean grammatical complexity score (adapted from Buckley, Pennanen and Archer, in preparation [TODO: references 115])
| Age | Male | Female |
|---|---|---|
| 3 | 1.5 | 6.2 |
| 4 | 9.2 | 5.7 |
| 5 | 7.5 | 11.4 |
| 6 | 9.0 | 18.4 |
| 7 | 10.7 | 17.0 |
| 8 | 15.8 | 33.0 |
[Table 11] illustrates that while there was no difference in overall vocabulary size for boys and girls in this study, the boys are slower than the girls at producing complex phrases. The researchers do not have any evidence that would explain this, but their clinical experience suggests that boys often have more severe speech production difficulties than girls and that this may be a partial explanation. More research is needed, which follows children longitudinally, to identify the causes of the wide differences in rates of progress between different children with Down syndrome of the same age and to explain any sex differences such as the one observed in this study.
Another illustration of the variation for emerging grammar is seen from the diary records kept of the progress of individual children.[6] [Table 12] illustrates the ages at which the children acquired the early bound morphemes explained in [Table 4].
[Table 12] indicates that if we take 12 months off the ages to allow for the 12 month delay in reaching production of 10 words, the children are mastering the morpheme rules in the same time from starting to talk as typically developing children.
Table 12. The comparison between the mean ages of acquisition of morpheme rules in children with Down syndrome and typically developing children (adapted from Rutter and Buckley, 1994[6])
| Progress | Mean age TD | Mean age DS | Mean age DS (minus 12 months) | Range TD | Range DS |
|---|---|---|---|---|---|
| The present progressive tense on verbs (-ing), denoting an activity in progress - e.g., "He’s drawing." | 28.7 | 40.8 | 28.8 | 21-35 | 30-52 |
| The preposition "on" - e.g., "Put it on the table." | 29.3 | 37.0 | 25.0 | 21-35 | 28-49 |
| The preposition "in" - e.g., "It’s in the cupboard." | 29.7 | 39.7 | 27.7 | 23-35 | 30-54 |
| The plural /s/ - e.g., "Dogs bark." | 30.3 | 41.2 | 29.2 | 25-34 | 28-50 |
| The irregular past tense of verbs - e.g., "It broke", "He ran away", "I made it." | 32.7 | 39.6 | 27.6 | 28-35 | 28-51 |
| The possessive /s/ - e.g., "Tom’s book." | 33.3 | 38.8 | 26.8 | 25-39 | 31-52 |
| The uncontractable copula "be" form (that is, where the "be" form is used with an adjective, preposition or noun phrase and cannot be abbreviated) - e.g., "He is." (In response to "Who’s there?") | 33.3 | —– | —– | 27-38 | —– |
| The articles "a" and "the" | 35.3 | 41.1 | 29.9 | 29-39 | 31-56 |
| Regular past tense forms - e.g., "Sally picked a flower." | 39.0 | 47.7 | 35.7 | 26-48 | 40-54 |
| The third person singular /s/ for present tense verbs - e.g., "John rides the bike"; "He likes my dress." | 39.0 | —– | —– | 30-45 | —– |
| Irregular, third-person singular present tense; the verbs "have" and "do" become "has" and "does" for third-person sentence subjects - e.g., "He has two eyes"; "Mummy does the shopping." | 40.0 | 44.0 | 32.0 | 31-50 | 44-44 |
| The uncontractable copula "be" form (that is, where the "be" occurs with a main verb and cannot be abbreviated) - e.g., "He is." (In response to "Who’s coming to the party?") | 41.7 | —– | —– | 32-49 | —– |
| The contractible copula form (that is, where "be" occurs with an adjective, preposition or noun phrase and where abbreviation is possible) - e.g., "They’re inside"; "The boy’s dirty." | 42.7 | 51.5 | 39.5 | 33-50 | 42-79 |
| The contractible auxiliary "be" form (that is, where "be" occurs with a main verb and abbreviation is possible) - e.g., "He’s laughing"; "Mummy’s cooking dinner." | 43.3 | 44.7 | 32.7 | 34-50 | 44-45 |
|
Key: TD = Typically developing children DS = Children with Down syndrome |
|||||
The data reported in an American study of 168 children published by Libby Kumin and colleagues in Maryland, USA, illustrates the same wide range of individual rates of progress. This study documents the children’s progress with total productive vocabulary and this includes words that are signed as well as those spoken, which may account for the rather larger vocabulary sizes for each age than are reported in the English data. For example, while the average vocabulary in speech and sign was 168 at 3 years of age, the range was from 5 to 675 words for the children studied. Similarly, at 6 years, the average vocabulary was 468 words but the range for the children was from 57 to 652 words.[8]
By 5 years of age all the American children were using multi-word utterances, 27% sometimes and 73% often. At this age, 54% were using plurals sometimes, 23% often and 23% not at all. At 6 years of age, 60% were using the possessive ‘s’ often and 33% sometimes and 7% not at all.
The reader may observe that the children from the English studies ( [Table 12]) are reaching some of the early grammar milestones earlier than the American children. This may be because the English children were taking part in a study and their parents were observing and recording their development on a monthly basis. This may have made them more aware of their children’s progress and also more responsive to their language learning needs.
The practical modules for speech and language, and for reading, in this series encourage recording of children’s progress, as it is not only necessary for selecting intervention targets and recording progress, but it may also encourage and inform teachers and parents, and so influence progress.
Teenagers and adults
The speech and language skills of teenagers with Down syndrome
- Speech and language is more delayed than non-verbal ability
- 97% will be using speech as their main form of communication
- Some will still be using signs as an important aid
- Most will be talking in short, keyword or simple sentences
- Sentence length and grammar slowly improves into adulthood
- Speech intelligibility is a continuing issue which may limit community participation
- Improvement in speech and language is possible for most teenagers and adults with therapy and effective inclusion
There is not as much detailed information available on the progress of speech and language skills during teenage and adult years as there is for children and the information that is available from standard tests shows that most young people with Down syndrome are still progressing steadily, but quite slowly in terms of fluent sentence production.[27],[28]
Teenagers continue to steadily learn vocabulary and their vocabulary knowledge is ahead of their grammar knowledge. In grammar, they have more difficulty with function words in comprehension and production than with the bound morphology. Their sentence lengths do slowly increase and they are more fluent when talking in narrative style (story or event reporting) than in conversation (often question and answer).
Their understanding of grammar is ahead of their ability to use it in sentences, and much of their difficulty may be due to their speech production difficulties.[21] Many teenagers and adults will communicate quite effectively but still in short keyword sentences, and they may be less inclined to start conversations than other teenagers. This may be because of the repeated experience of not being understood when starting a new topic.[29],[14]
In one teenage study in 1987, three out of 90 young people had no speech at all. For the 87 with speech, parents were asked about the length of utterance their teenagers used, as an estimate of productive grammar. While 70% of all the girls (at 11 to 17 years) and the older boys (14 to 17 years) regularly used sentences of five words or more, only half the younger boys did so. Conversely, 18% of the younger girls and 33% of the younger boys were limited to communicating in three word utterances or less, and 10% of the older teenagers were equally limited.[30]
In a further teenage study in 1999, the same authors were able to compare the progress of a new cohort of teenagers living in the same area as the 1987 group. [TODO: references 82],[31] In this second study, it was possible to compare the progress of teenagers who had been in mainstream schools with those who had been in special schools throughout their school career. All the teenagers (100%)in inclusive school placements were using sentences of 5 or more words and 83% were using complete grammar, whereas for those in special schools in 1999, 61% were using sentences of 5 or more words and 52% using grammatically complete sentences. This suggests that more stimulating environments and higher expectations are helping all children with Down syndrome, but that being in a normal language environment in an ordinary school is particularly beneficial.
The teenagers included in the mainstream schools were more than two years ahead in spoken language skills and more than 3 years ahead in literacy skills when compared with the teenagers in the special schools. There is no evidence that the two groups varied in ability at the start of their school careers.
Considering speech intelligibility rather than structure, in 1987, 42% of the teenagers could be understood by strangers, for example, if they were in a shop or restaurant and asking to purchase something. In 1999, 78% of the mainstreamed teenagers and 56% of the special school teenagers were reported to be understood by strangers in the community. About 90% of the teenagers in all the groups are understood by parents, teachers and those familiar with them.
These data do illustrate that the speech and language skills of most people with Down syndrome can improve if they are in more stimulating language environments. Most of these teenagers have not had significant amounts of speech and language therapy, so with targeted intervention as well as immersion in normal language environments, it is probable that much more progress could be made.
More severe speech and language difficulties
Some 10-15% of children with Down syndrome are significantly more impaired in speech and language skills and make significantly slower progress than most children with Down syndrome. Some of the children in this group have additional medical problems[30] and some have additional brain damage, so are slower in all areas of development and remain more dependent throughout their lives. Some of the group have more profound language learning difficulties, for reasons which are not clear, and some children are severely to profoundly deaf with losses greater than 60dB.
Autism
A few children with Down syndrome show autistic profiles and these children do not have good non-verbal skills such as eye-contact or smiling and they are not keen to communicate.[32],[33] In our experience, some children who appear ‘autistic’ in later childhood did have typical early non-verbal skills but did not go on to develop sign or speech and slowly became more withdrawn and ‘autistic’ over time. Some of these children are the ones with the more severe hearing losses.
In the author’s view, the dual diagnosis of autism and Down syndrome is being made too often and is only accurate in about 3-4% of children. Many of the children being labelled autistic have severe communication difficulties that could be improved and they do not have some underlying fundamental autistic type of social impairment. A greater number of children with Down syndrome do have some of the behaviours that are seen in ‘autistic spectrum’ disorders, at times during their development, as do many children with significant developmental delays but not Down syndrome. As their ability to communicate, to play and gain control over their daily lives improves, these ‘autistic like’ behaviours diminish in frequency.
Dyspraxia
Other children in the group that is more delayed in speech and language, are those with unusually severe speech production difficulties, which we would define as dyspraxic (neuromotor difficulties in producing the learned patterns of movement required for speech). Often these children do not have delayed comprehension early on, at the first word stage, but if they have very great difficulty making sounds and then words, this will have a significant impact on their experience of communicating and rate of language learning. Most of these children make slow but steady progress with speech during primary school years. It is important that the children with dyspraxic difficulties are identified as early as possible and that they receive more intensive and specific speech therapy than children with Down syndrome who do not have dyspraxia.
Explaining the profile of speech and language development
If we are going to try and improve the development of speech and language skills for children with Down syndrome, we need to identify as many of the specific reasons for their difficulties as possible. We have some pointers but by no means a complete picture of the causes let alone their interactive effects on the children’s progress. This section provides an overview of the current factors thought to contribute to the typical profile of speech and language difficulties for individuals with Down syndrome.
Learning or cognitive difficulties
Some of the reasons for the speech and language difficulties
- Learning difficulties - need more examples to learn
- Anatomical differences - affect speech skills
- Learning language from listening is affected by:
- hearing loss
- auditory discrimination
- verbal short-term memory
- Speech motor difficulties:
- delay vocabulary and grammar development
- affect the way a child is talked to and included in conversations
- Joint attention difficulties and slow development of speech will both reduce language learning opportunities
All these difficulties can be targeted with appropriate and effective intervention strategies
Children with Down syndrome may be slower to understand the world around them and they may need more opportunities to link words to meaning than other children. If a typically developing child needs to hear the word ‘’cat’’ 5 or 6 times while looking at the cat, in order to make the link, the child with Down syndrome may need 10 or 12 times. No one knows exactly how many times either group of children need the experience to learn a word, but it is likely that the slower learning child needs more. Typically developing children pick up the meanings of words as they are used within sentences in everyday activities. Parents do not point to the cat and say ‘’cat’‘. They probably say things like’‘Look, there is the cat’‘, or’‘The cat is hungry’’. Children with Down syndrome may find learning word meanings from sentences more difficult, and will be helped by extra opportunities to learn from language teaching games in which words can be learned one at a time. This will be particularly helpful for early vocabulary, when it is mainly nouns and verbs that are being learned. Later, specific teaching of early grammar and sentence meanings may also help to accelerate learning.
Physical differences
The anatomical differences associated with Down syndrome, such as differences in skull shape, jaw, palate, dentition, tongue size relative to mouth and difficulties with motor skills development and fine movement control, will all contribute to the greater difficulties that children with Down syndrome have in developing clear speech. Therapy aimed at increasing oral-motor control from infancy will help articulation but there is no evidence that surgery for tongue reduction improves speech.[34]
Hearing loss
There are consistent reports highlighting the high risk of mild to moderate hearing loss for children with Down syndrome.[35] This is usually conductive loss due to ‘glue’ in the middle ear and therefore fluctuates over time. It affects up to 70% of children in their early years.[36] There is also an increased likelihood of sensori-neural loss (‘nerve deafness’) and this will have a permanent effect on hearing ability. In the author’s view, the significance of this high incidence of hearing loss on language learning is still underestimated. The long-term effects of glue ear are also not trivial. Michael Marcell and colleagues have demonstrated that as many as 40% of young adults may have permanent middle ear dysfunction and that these young people have poorer speech and language skills than those without the loss. Not only was their language knowledge less, they were also impaired on immediate speech recognition tasks.[37]
Auditory discrimination
In our practical experience, we see children who have difficulty in discriminating between similar sounding words, such as ‘dolly’ and ‘lolly’, ‘red’ and ‘bread’, ‘horse’ and ‘sauce’ even when their hearing is within normal limits. This will make it very difficult to learn to understand the words that they are hearing as toddlers and slow up vocabulary comprehension.
These examples are taken from one of our children’s case histories. The child wanted to use a single sign for each pair of words although he could demonstrate comprehension of the different meanings. We could conclude that he was only hearing ‘olly’, ‘ed’ and ‘orse’ for each of the pairs and he must have been very confused by the adult language system. To him it must have seemed as if we have one word for very different things! We suspect that this may be a common experience for children with Down syndrome. Imagine how much more difficult this would make language learning. (Children do have to cope with learning to understand ‘I’ and ‘eye’, ‘so’ and ‘sew’, ‘sail’ and ‘sale’ but the discrimination problems described will further increase a child’s learning difficulties).
Working memory
Working memory for individuals with Down syndrome
- The growth in verbal memory span during childhood is specifically delayed in children with Down syndrome
- This will affect the learning of words and grammar
Working memory is the system that holds incoming verbal and visual information long enough for the brain to process it for meaning (not to be confused with long-term memory which is not generally impaired in persons with Down syndrome). The capacity of the verbal short-term memory part of this system can be estimated by finding out how many digits, said in random order at the rate of one per second, a child can repeat immediately in the same order (digit span). Typically, this digit span increases during childhood from about 3 digits at 4-5 years to 6-7 digits at 16 years.[38],[39]
Research has indicated that this system is linked to the listener’s efficiency of speech perception and speech production, and children usually get quicker at recognising and reproducing speech as they get older as a result of practice. Research has also shown that the efficiency of this verbal short-term memory system influences the speed at which children learn new vocabulary and learn to read. It is also thought to play a significant role in the processing and comprehension of speech and in organising speech production.[40],[39]
For children with Down syndrome, short-term memory span does not usually increase with age at a typical rate and most teenagers and adults only have spans of 2 to 4 digits.[21],[25], [91-94] The research on the significance of digit span in typically developing children suggests that this will delay vocabulary learning. It might be predicted to have an even bigger negative effect on the children’s ability to master grammar as this will usually require the ability to hold a whole phrase or sentence in short-term store in order to process it for meaning. There is some evidence that memory training can increase the short-term spans for children with Down syndrome and that improved span increases the rate at which grammar is learned.[41]
Learning language from listening is compromised
The difficulties in hearing, auditory discrimination and working memory can be summed up as indicating that learning language from listening, the way most babies do, will be difficult for children with Down syndrome.
Speech motor difficulties
The lack of clarity in the speech of most children with Down syndrome is likely to be due to a number of difficulties ranging from less effective operation of some or all of the brain mechanisms needed to plan and organise speech production to difficulties in moving the oral facial muscles and tongue with precision.[42],[11],[13],[43],[44]
The children have more difficulty establishing precise control over the muscles of the mouth, tongue and larynx, and this early control is influenced by sucking and chewing patterns and progress. Even if these speech mechanisms work effectively, the children may be having difficulty in hearing speech sounds and word patterns clearly enough to establish good templates to guide their production. They then have difficulty mastering speech sounds and using them in words.
Some observers suggest that it may take children with Down syndrome longer to find the words that they want and to organise sentences.[45] Working memory and information processing capacity may be relevant here and limiting the children’s progress.
The delays in producing first words and sentences severely reduces the amount of speech practice that children with Down syndrome experience, further adding to their delays in progress relative to typically developing children. These delays are also likely to reduce the amount of talk to and with children with Down syndrome.
Learning interactions and opportunities
The risk, then, is that children with Down syndrome will experience fewer language learning opportunities from infancy and throughout life, when it can be argued that they are likely to need more quality opportunities than typically developing children to learn language at an adequate pace. The evidence that babies with Down syndrome are not quite as good as typically developing babies at initiating joint attention sessions, maintaining attention on the task or switching attention between tasks suggests that they will need carers who are aware of these issues and who plan to compensate for them. Throughout childhood, everyone needs to be aware and try to compensate for the delayed and limited production of speech, recognising that this is likely to reduce the quality and quantity of opportunities to learn and to practice language and communication skills.
Summary
- Children with Down syndrome usually experience considerable delay and difficulties with learning to talk.
- Their social interactive skills and non-verbal communication skills are a strength, but speech sound production is a specific weakness.
- Vocabulary learning, while delayed, is also a strength but grammar learning is a weakness.
- Children with Down syndrome show the same progression from one word to two word utterances, when they have 50-100 word (or signs) in heir production vocabulary, as other children and they show the same progression to early grammar in their speech when they have 300-400 words. Unfortunately the usual delay in reaching 300-400 production words (at 5 to 6 years or even older, instead of at 2 to 3 years) may compromise their ability to master fully sophisticated grammar and phonology in later speech.
- Progress in language learning is probably compromised by hearing difficulties for most children with Down syndrome. It is certainly compromised by the children’s specific difficulty with speech sound production, at all ages.
- Progress in both vocabulary and grammar learning are influenced by poor working memory capacity for age throughout childhood.
- The children’s spoken language difficulties reduce their participation in everyday conversations, at home and at school.
- The slow rate of language learning affects progress in all aspects of cognitive development - particularly learning, remembering, thinking and reasoning
- This information provides some clear guidelines for priorities in speech and language intervention programmes. All these difficulties can be directly addressed with specific interventions. It should be noted that many other children (without Down syndrome) experience some or all of these difficulties and benefit from similar approaches to therapy.
