Motor cortex compensates for lack of sensory and motor experience during auditory speech perception

Listening to speech has been shown to activate motor regions, as measured by corticobulbar excitability. In this experiment, we explored if motor regions are also recruited during listening to non-native speech, for which we lack both sensory and motor experience. By administering Transcranial Magnetic Stimulation (TMS) over the left motor cortex we recorded corticobulbar excitability of the lip muscles when Italian participants listened to native-like and non-native German vowels. Results showed that lip corticobulbar excitability increased for a combination of lip use during articulation and non-nativeness of the vowels. Lip corticobulbar excitability was further related to measures obtained in perception and production tasks showing a negative relationship with nativeness ratings and a positive relationship with the uncertainty of lip movement during production of the vowels. These results suggest an active and compensatory role of the motor system during listening to perceptually/articulatory unfamiliar phonemes.