The development of oral motor control and language
Department of Psychology, Lancaster University
Abstract – Motor control has long been associated with language skill, in deficits, both acquired and developmental, and in typical development. Most evidence comes from limb praxis however; the link between oral motor control and speech and language has been neglected, despite the fact that most language users talk with their mouths. Oral motor control is affected in a variety of developmental disorders, including Down syndrome. However, its development is poorly understood. We investigated oral motor control in three groups: adults with acquired aphasia, individuals with developmental dysphasia, and typically developing children. In individuals with speech and language difficulties, oral motor control was impaired. More complex movements and sets of movements were even harder for individuals with language impairments. In typically developing children (21-24 months), oral motor control was found to be related to language skills. In both studies, a closer relationship was found between language and complex oral movements than simple oral movements. This relationship remained when the effect of overall cognitive ability was removed. Children who were poor at oral movements were not good at language, although children who were good at oral movements could fall anywhere on the distribution of language abilities. Oral motor skills may be a necessary precursor for language skills.
Keywords: oral motor control, language development, developmental language disorders, gesture
Evidence for a link between motor control and language
In examining the relationship between motor control and language development and disorders, there is a contrast between the large amount that is known about limbmotor control and the small amount that is known about oral motor control. For example, it has long been known that the first stages of language development occur in parallel with the first stages of gesture development, and that children whose first gestures are earlier than average usually also say their first words earlier than average (Bates et al., 1979). Recent data also show that children who are late in the onset of both spontaneous communicative gesture and spoken language are more likely to remain delayed than those who start making communicative gestures at a typical age but whose speech is also delayed (Thal et al., 1997). There is also a strong association between limb motor control difficulties and language impairment (Hill, 2001), which appear to share a common genetic basis (Bishop, 2002). This imbalance in research exists despite the fact that the majority of language users speak, rather than sign. We now turn to work on the development of oral motor skills.
Associations in disorders
Much of the research into the relationship between nonverbal oral motor control and language development has been inspired by a multiplicity of studies showing that language dysfunction and oral motor dysfunction often occur together. My own research shows similar patterns of impairment in developmental and acquired verbal dyspraxia (Alcock et al., 2000b, see also details below).
Indeed, generally acquired oral dyspraxia and acquired nonfluent dysphasia are found to be associated (Mateer & Kimura, 1977). Although dissociations between these two have been found (Masdeu & O’Hara, 1983), the association is common enough to suggest a link of some kind; dissociations in adult acquired dysfunction do not necessarily suggest modularity in development (Karmi- loff-Smith, 1998).
Oral motor skill is found to be impaired in many developmental disorders where spoken language is also impaired: it is commonly impaired in autism (Adams, 1998; Amato & Slavin, 1998; Page & Boucher, 1998); oral motor difficulties are more commonly found in autistic children than limb motor difficulties. Oral motor control has frequently been found to be impaired in Down syndrome, and this seems to stem not just from oral weaknesses but to involve some degree of dyspraxia (Kumin & Adams, 2000; Kumin & Bahr, 1999; Spender et al., 1995).
In children with specific language impairment (SLI), very few studies have looked at oral motor control but in those that have, associations have been found. For example, Stark and Blackwell (1997) found that oral motor skills were associated with both nonword repetition and phoneme identification in SLI. There has in particular been a suggestion that developmental verbal dyspraxia cannot exist without nonverbal, oral dyspraxia (Stackhouse & Snowling, 1992). With these associations in mind, study 1 investigated the oral motor abilities of a group of individuals with a developmental speech and language impairment, the KE family.
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