Stimulating speech: auditory-motor interactions in perception and production

Kate WATKINS Professeure à l’Université d’Oxford

I will describe a series of experiments employing non-invasive brain stimulation in combination with measures of brain function, which explore how motor-to-sensory and sensory-to-motor interactions can be modulated during speech perception and production tasks.

To study the role of the motor cortex in speech perception, we use transcranial magnetic stimulation (TMS) to temporarily disrupt the motor cortex representations of the articulators.  We then record the effects of this disruption on speech perception using behaviour, EEG and MEG.  We found that the motor cortex contributes to early stages of speech processing in the auditory cortex but not to processing of non-speech stimuli.  The early effects are left-lateralised and can be fine-tuned by attention.   We recently explored these lateralised effects further using perception of lexical tones in Mandarin and non-tonal language speakers.  The effect of speech motor cortex disruption is left-lateralised for tone perception in Mandarin speakers and right-lateralised for non-tonal language speakers.

We have also explored the effects of anodal transcranial direct current stimulation (tDCS) over speech motor cortex and the cerebellum on speech adaptation to a formant perturbation suggesting different contributions from these regions to the adaptation process.

Taken together our work demonstrates the strength of brain stimulation methods especially when used in combination with other measures. The work presented confirms the importance of interactions between motor and sensory systems that are necessary for both speech perception and production.