Led by Professor Maggie Snowling, Professor Charles Hulme and Dr Emma Hayiou-Thomas this five-year, longitudinal study funded by the Wellcome Trust investigates the nature of the overlap between dyslexia and specific language impairment.
It is widely accepted that children who have pre-school speech or language difficulties are at risk for developing later literacy difficulties and that children who go on to develop dyslexia have early language weaknesses. This study has been tracing the development of three groups of children from the age of ~3 years old to ~7 years old:
- Children from a family where there is a history of dyslexia
- Children who have pre-school speech and / or language difficulties
- Children who are developing typically
The project was divided into five phases based on age. Each phase involved a different test battery which was specifically designed to look at certain literacy and phonological skills. There were 260 children in the initial sample; this is now n=241 (attrition to date = 19).
To confirm 'dyslexia-risk' status, the team aimed to assess both parents of each child in the study (where possible). Parents also completed a self-report questionnaire. More than 350 parents were formally assessed on tests of literacy and phonological skills.
In 2011, 60 children from high-risk groups already showing reading delay one year after starting school were selected to receive a specially designed intervention to promote language and literacy skills - RALI (Reading and Language Intervention). The children started the intervention once they had completed the Phase 4 assessment; the first 30 children took part from April-December 2011 and the second 30 children took part from September-March 2012. In each of these groups, children were randomly allocated to an intervention group for 18 weeks or a waiting control group (9 week intervention).
The children were based in 46 different schools and in each school the target child was taught together with peers from the same class. A teaching assistant from each school was trained to deliver the intervention and received support/observation from the research team.
Researchers on the RALI part of the project aimed to discover whether a theoretically motivated intervention can improve the reading skills of children whose reading development is delayed at 6 years. RALI also enabled the research team to consider the extent to which responsiveness to intervention relates to the severity of underlying cognitive and language deficits.
In addition to RALI the Wellcome project has investigated the contribution of the home literacy environment on reading skill development and, in collaboration with other groups, looked at DNA samples to identify gene markers for dyslexia and SLI.
Latest key findings
- Approximately one third of children at family risk of dyslexia meet diagnostic criteria for a preschool language impairment.
- Children at family risk of dyslexia who also meet criteria for a pre-school language impairment resemble other children with a pre-school language impairment but no family risk of dyslexia. However, they do appear to have better vocabulary knowledge and are more able to correctly inflect verbs in their speech. Interestingly, they do more poorly on a RAN task which requires the rapid access of verbal information from pictures. Both groups of children have trouble hearing and manipulating the sounds in spoken words and are finding it difficult to learn early literacy skills, such as letter sounds.
- In the group of children at family-risk of dyslexia who do not meet criteria for a pre-school language impairment there is a lot of variability in language and early literacy skills. As a group, they show weaknesses in hearing and manipulating the sounds in spoken words and in mapping between visual and verbal information.
- Children with a pre-school language impairment, with or without a family risk of dyslexia, have weaknesses in fine motor skills and attention. This suggests that they may be at increased risk for co-morbid difficulties such as attention deficit hyperactivity disorder (ADHD) or dyspraxia.
- Those children who are at family-risk but who do not have a pre-school language impairment do not appear to have these co-morbid motor or attention difficulties.
In summary, our findings suggest that there may be multiple risk factors for early literacy difficulties. These are:
- Difficulties hearing and manipulating the sounds in spoken words
- Difficulties mapping between visual and verbal information
- Co-morbid motor and attention difficulties