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Introduction

Speech and language skills are an area of particular difficulty for most children and adolescents with Down syndrome, even though they are keen to communicate right from infancy and usually have strengths in non-verbal communication skills such as gesture and sign. Spoken language skills are usually delayed relative to the children's non-verbal ability and this suggests a profile of specific language impairment. This should be a focus for targeted and intensive intervention throughout infancy and childhood, as it is in other language impaired children who show a gap between verbal and non-verbal abilities.

There has been a considerable amount of research effort over the past thirty years focused on understanding the speech and language profile associated with Down syndrome. In the last ten years there have been many important papers,^[1-7] book chapters^[8-21] and books^[22-24] published on speech and language development in individuals with Down syndrome, and the reader wishing to read the literature in more detail is advised to consult these. These publications have all contributed to an increased understanding of the language learning needs of children with Down syndrome. There is now considerable agreement among the experts on the principles which should guide effective interventions.^{[1,4,9-12,24-27]}

This module explains speech and language development, highlighting the key findings from research into

1. the processes and influences on speech and language development in typically developing children
2. the specific speech and language difficulties of children with Down syndrome and their possible causes
3. effective interventions

This module should be read before using the accompanying practical modules.

The importance of learning to talk

Learning to talk is the most important thing that children do. It is central to all other aspects of their development. It is critically important for social and emotional development and for the development of cognitive or mental abilities. This is a theme that will be explained and reinforced as the module develops.

Speech and language skills are central to social interaction

Being able to talk allows children to gain control over their social and emotional world. Talking enables children to ask for what they want, to share experiences, to understand what is about to happen, and to express themselves when they are hurt or upset. In short, talking enables children to relate to others.

By the preschool years, being able to communicate enables children to play together, to share and to learn together. In school and throughout life, communication underpins the development of friendships, the sharing of experiences, supporting one another, and negotiating our way through the world - shopping, travelling and working.

Being able to talk also underpins the development of mental abilities

It is important to note that word learning begins in the first year of life and continues to old age. Words are knowledge. Each new word learned is a concept learned and the rate at which words are learned reflects the rate at which we are gaining knowledge about our world. As language skills develop, words become a tool for thinking. Once children begin to string words together, words take over as the most powerful way to think and reason and remember - we do these things most often as silent speech in our heads.

The human brain has clearly evolved to be very efficient at developing spoken language and using language as a tool for other mental processes, such as working memory.

Working memory is the short-term memory system that supports the initial processing of incoming spoken and visual information as well as current mental activities such as reading text or adding sums. It is typically a speech-based system and its efficiency increases as children's speech processing and speech production abilities improve. Speech and language skills also influence, and are influenced by, progress in reading skills.

In summary, talking underpins our mental development and our ability to interact with the world around us. Talking is not the only way to communicate and we all use many non-verbal means to express ourselves in addition to words, however words are the most powerful form of communication for social life and for learning.

This module focuses on the development of spoken language as almost all individuals with Down syndrome will use speech as their main mode of communication after five years of age. Signs may be used as a bridge to teaching spoken language skills but these signs should be 'keyword' signs used to augment spoken words, they are not taught as an alternative language. Signs may continue to be helpful throughout life for many individuals with Down syndrome to support their spoken language, as their speech often remains difficult to understand.

The skills and knowledge needed for talking

A complex range of knowledge and skills interact to give us our ability to communicate by talking. These can be considered under three main headings - interactive communication skills, spoken language knowledge and speaking. Spoken language knowledge can be further subdivided into vocabulary and grammar. In Table 1 the terms that professionals may use for these different aspects of talking are included in brackets.

At any age, children's progress in all areas (i.e. in interactive communication skills, vocabulary knowledge, grammar knowledge and speech skills) always need to be considered. These skills are acquired over a period of years from infancy through primary and secondary school and a great deal is known about the processes that influence their development in typically developing children.

Table 2 provides a guide to the way in which progress in each area relates to ages and to stages of development in typically developing children. The table describes the milestones for children's spoken language skills in each area. Most children will understand these actions, words and grammar in everyday communication earlier than they are able to use them in their speech. Therefore, when assessing children's language skills, production and comprehension of vocabulary and grammar are assessed separately.

The range of skills required for individuals with Down syndrome to communicate are no different from the range of skills employed by anyone else. Unfortunately, a number of difficulties with the skills required for speech and language are associated with Down syndrome. Promoting these skills and helping children with Down syndrome to overcome these difficulties is clearly fundamental for all aspects of their social and mental development. The way in which each of the skills develop in non-disabled children is discussed in the following section to set the scene for understanding the difficulties faced by children with Down syndrome and ways in which they may be reduced or overcome.

Learning to talk is an everyday activity

Children learn to talk because they want to communicate. Communicating with gestures in infancy leads to communicating with words and sentences. Children learn to talk as they take part in all the ordinary, everyday communication that they experience during their waking hours. The quality and quantity of the language that they experience as they are talked to each day influences the rate at which children progress with learning to talk. ^[28-30]

Parent's talk styles influence children's progress

Longitudinal research by Hart and Risley ^[29,30] indicates that the amount and quality of talk that typically developing babies are exposed to each day varies considerably in different homes. The more children were talked to, the faster they expanded their vocabulary. The children who were talked to the most had the highest Verbal IQ scores at 4 years, also supporting this author's argument that language learning is fundamental to the development of cognitive skills or mental abilities.

Verbal IQ was specifically influenced by the amount that parents participated in activities with their children and included their children in conversation as they went about daily chores, by the total amount of words and range of different words that parents used with their children, by parent's responsiveness to their children's attempts to initiate communications and by the way in which parents responded. Positive response styles included extensions and expansions of the child's utterance, which help to teach grammar. They also included a style which asked, rather than told, children to do things.

Emotional style turned out to be particularly important as the children of parents who regularly used a negative style, that is, saying ''no'', criticising the child and prohibiting activities made much slower progress with their language development than the children of parents who regularly had a positive style and praised, encouraged and conveyed delight at their children's efforts. Children also learned to talk like their parents, using orders and being negative and bossy in style or using explanations and asking politely, depending on parent style.

Play activities and book reading

Studies have shown that, while including children in conversations throughout the day is important, the language that parents use when joining in toy play activities and reading books with children provides the richest sources of language experience for their children.

Children learn, and later use, the language that has been addressed to them in specific contexts repeatedly, as is illustrated by the early use of 'bye-bye', 'all gone', 'more' and by the learning of responses in games and from singing action or nursery rhymes. Learning from regular repetition in social situations and from games is probably even more important for children with language learning difficulties.

Social learning with other children

As children move beyond the family to preschool and school settings, the opportunities to communicate with a wide range of partners develop. The quality and quantity of these social opportunities, particularly with peers, will also influence all aspects of speech and language development.