Lexical Tone Perception in Tone Language speakers--a fMRI Study

Tone language refers to a language that uses fixed pitch pattern to distinguish words (Yip, 2002). Cantonese is one of the main tone languages spoken by over 70 million around the world (Li et al.,1995; Adolfsson, 2010). Individuals with significant hearing impairment often present great difficulty in tone perception, affecting their understanding of words and hence, hamper their overall communication. The poor tone perception persists even with intensive auditory training coupled with advanced hearing technology such as cochlear implants.

Understanding the functional anatomy of the brain during lexical tone processing will provide useful hints for an effective intervention strategy such as brain stimulation. Researchers have been investigating the neural basis for tone perception in the past decades but failing to come to a consensus on the location of the brain that is responsible for lexical tone processing. The discrepant results may be due to the fact of the differences in subject selection (animals, healthy adults, brain-injured patients, tonal-language and non-tonal language speakers), testing materials and tasks employed (linguistic versus non-linguistic stimuli; dichotic listening versus discrimination and identification tasks) and outcome measurements (performance score, reaction time, accuracy rate, PET scan and fMRI).

Cortical organization, or brain mapping, refers to functional anatomy of the brain. The present study is the first study to systematically investigate the cortical organization of the brain in lexical tone perception of Cantonese speakers by the use of functional magnetic resonance imaging (fMRI). A comprehensive set of auditory stimuli specifically for investigating the different levels of lexical tone processing will be constructed. Native Cantonese speakers with normal hearing were recruited. They underwent fMRI while listening to the carefully designed auditory stimuli.

Once the cortical organization of lexical tone processing in Cantonese is identified, the valuable findings could be applied in further brain intervention procedures to tackle the long lasting, unresolved tone perception difficulty encountered by people with hearing impairment or other related disorders.