Brain lateralisation of speech and language production

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For most people, the left side of the brain (hemisphere) is critical for their ability to use language. Most research into language and the brain has only considered auditory spoken languages used by hearing people, such as spoken English. However, language is more than speech. This is especially clear when we think about individuals born deaf who learn language without full access to auditory speech. There is huge variability in the language backgrounds of people born deaf. They might primarily use speechreading and spoken English to communicate. They may use an amplification device such as a hearing aid or cochlear implant. Some learn a signed language such as British Sign Language (BSL). My PhD research used a simple tool for measuring brain activity in children born deaf. This method, called functional transcranial Doppler sonography (fTCD), can be used while children produce spoken or signed language. This means we can test hypotheses about whether language - not only speech - is more reliant on the left than the right hemisphere of the brain. If so, we can also address questions about why this is the case.I found that children born deaf, regardless of their language background, showed typical left hemisphere dominance when they produced language. During a series of experiments, I also found that lateralisation measured by fTCD is affected by the types of task people are asked to do. I developed a picture naming task which showed greater left hemisphere activity in hearing children, but only those who were fluent at naming pictures. This study was the first to establish a link between fTCD data and behaviour.One of the aims of my fellowship is to communicate the findings described above with the academic community by writing papers for publication and by presenting the work at an international conference. A second aim is to communicate those findings with teachers of deaf children, to make sure my research goals are in line with those of research users. I will also make a short video to circulate on social media with the aim of debunking the right brain/left brain 'neuromyth'. There are some educational interventions which target developmental disorders such as autism and dyslexia that make claims about differences between the processes of the left and right hemispheres. I hope to highlight that these interventions may be overly simplistic.Another aim is to develop my skills as a researcher. My work would benefit from understanding more about the way fTCD measures hemispheric dominance. Gaining training in functional Near Infrared Spectroscopy (fNIRS) would allow me to compare the two methods and find out which regions show the greatest differences between hemispheres during language production. Skills using fNIRS will be crucial to my future project plans.Finally, I will use time in this fellowship to consolidate plans for my future programme of research. The overarching theme of this future work would be to describe the cognitive and neurocognitive operations that babies begin to perform very early in life to lay the foundation for producing language in childhood. A novel way to approach this is to investigate language learning in children who have drastically different early experience of language. My primary mentor, Dr Evelyne Mercure, tested the neural responses to language of 99 hearing children (as babies), including 31 hearing infants with Deaf mothers who are acquiring two languages in different modalities. Following up this unique cohort would allow me to ask a set of interesting questions about early language experience and its effects on the brain. To develop a structured programme of research for future research applications requires dedicated reading and writing time, and time to collect pilot data. An ESRC postdoctoral fellowship provides the perfect opportunity for me to achieve this.