Seeing speech

26 March 2009

Professor Ruth Campbell and Dr Cheryl Capek from University College London have explored how the brain ‘sees’ language when it is presented as silent speech and sign language.

They used functional magnetic resonance imaging (fMRI) to measure brain activity as deaf and hearing participants processed silently spoken word lists. The left superior temporal cortex was strongly activated in all participants - but significantly more so in deaf people. The area that was especially strongly activated includes auditory regions, which are usually activated when hearing people perceive sounds.

When deaf people watched sign language, similar parts of the brain were activated by the hand signs and by the silent mouthing of the corresponding word, but speech-like mouthing activated the auditory regions to a much greater extent.

The parents of deaf children awaiting cochlear implants are often advised not to mouth or sign words to their children before fitting, in case this affects the sensitivity of the auditory regions. The researchers call for a reconsideration of this practice, as their work suggests that watching speech might help children with implants to map the ‘new’ auditory stimulation to the seen speech patterns they have already been exposed to.

Also at University College London, Wellcome Trust Intermediate Clinical Fellow Dr Alexander Leff and colleagues have been using fMRI to study speech perception in the brain. Building on previous studies in the field, which have identified brain regions activated by hearing speech, the researchers have been able to model how the different regions interact and link together.

Ultimately, they hope that a better understanding of these links will be useful when developing treatments for conditions in which the brain’s speech perception system is damaged, such as stroke.

Reference

Campbell R and Capek C. Seeing speech and seeing sign: insights from a fMRI study. Int J Audiol 2008;47 Suppl 2:S3–9.

Leff AP et al. The cortical dynamics of intelligible speech. J Neurosci 2008;28(49):13209–15.