The goal of the project was to understand how the two sides of the brain process language, and whether individual differences in functional brain asymmetry have significance for language competence.
This question is of societal importance because language is such a fundamental ability for human achievement and interaction, yet we understand rather little about how the brain mediates this skill, and why some people have language limitations. More distally, there are implications for assessment of cerebral lateralisation in neurosurgical patients, where it is important to evaluate language localisation prior to surgery.
Our overall objectives were to discover whether we can treat language lateralisation as a unitary function, or whether different language skills can be differently lateralised, and whether such variation has any functional significance.
We were able to show conclusively that language lateralisation is not unitary; rather at least two factors are needed to account for individual variability in language functioning. The first factor seems to largely reflect language generation, and is lateralised to the left hemisphere in most people. Language functions focused more on comprehension and interpretation of language may be strongly lateralised in individuals, but with less of a population bias to one side. There is suggestive evidence that language difficulties are more common in individuals who have different language functions mediated by opposite hemispheres, rather than both being mediated by the left side.
In the course of conducting these studies, we have developed a range of new language assessments, some of which can be administered online, which are useful for pinpointing language deficits in adults as well as children.
